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Effect of rearing environment and environmental enrichment on behavior and neural development in young pigs
Grandin, Temple, Ph.D.
University of Illinois at Urbana-Champaign, 1989
UMI 300N.ZeebRd. Ann Arbor, MI 48106
EFFECT OF REARING ENVIRONMENT AND ENVIRONMENTAL ENRICHMENT ON BEHAVIOR AND NEURAL DEVELOPMENT IN YOUNG PIGS
BY
TEMPLE GRANDIN
B.A., Franklin Pierce College, 1970 M.S., Arizona State University, 1975
THESIS
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Animal Science
in the Graduate College of the University of Illinois at Urbana-Champaign, 1989
Urbana, Illinois
U N I V E R S I T Y O F I L L I N O I S A T U R B A N A - C H A M P A I G N
T H E G R A D U A T E C O L L E G E
DECEMBER 1988
W E H E R E B Y R E C O M M E N D T H A T T H E T H E S I S BY
TEMPLE GRANDIN
F.NTTTT.FT) EFFECT OF REARING ENVIRONMENT AND ENVIRONMENTAL ENRICHMENT ON
BEHAVIOR AND NEURAL DEVELOPMENT IN YOUNG PIGS
B E A C C E P T E D IN P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R
T H E D E G R E E O F DOCTOR OF PHILOSOPHY
W&^ Director of Thesis Research
Head of Department
Committee on Final Examinat ion!
Chairperson /7^<. _ _ _^
• Required for doctor's degree but not for master's
ACKNOWLEDGMENTS
As one gets to the end of the long road to a Ph.D., one
cannot help but reflect back on the events and people
instrumental in shaping the course of one's graduate program.
I am indebted to my major advisor, Dr. Stanley E. Curtis,
and my co-advisor, Dr. William T. Greenough. I will always be
grateful to them for allowing me to pursue the course of study
which led to this thesis. I also wish to thank Drs. Lynn A.
Barnett-Morriss, Tom R. Carr, the late Edwin M. Banks, and
Harold W. Gonyou for serving on my graduate study committee. I
extend special appreciation to Mr. Dale DeMotte; without his
assistance in developing the brain perfusion method, the work
on dendritic growth in the pig's brain would not have been
possible.
I am also indebted to Mr. Ian Taylor for assistance in
running my experiments and to Ms. Beth Palen for assistance
with neuron drawing and preparation of sections. Dr. Janice
Juraska provided invaluable assistance on developing a neuron
sorting procedure. I also gratefully acknowledge those who
unselfishly shared their statistical expertise: Mr. Robert
Hurst, Dr. Tina Widowski, and Mr. Dan Waldron. Others who
helped make this project possible include: Ms. Diane Bell, Dr.
James M. McFarlane, Mr. Michael Bilta, Ms. Rhonda Feinmehl, Mr.
Eric Fugate, Ms. Kathryn Russell, Ms. Mary Ellen Rowland, and
Mr.Kevin Walter. I also wish to thank the staffs at the Swine
Research Center and the Meats Laboratory.
m
TABLE OF CONTENTS
CHAPTER Page
I. INTRODUCTION.' 1
II. LITERATURE REVIEW 2
A. Effects of Environmental Restriction and Complexity : 2
Behavioral effects of environmental restriction 2
Central nervous system effects of environmental restriction 4
Concept of optimal stimulation 7 Structural changes in the brain 8 Farm animals 10
B. Environmental Enrichment Methods 11 Choice of environmental enrichment 11 Play in farm animals 13 Activity patterns in livestock 14 Aggression and environmental enrichment. 15
C. Thesis Research Outline 16 Dendritic growth in the pig's cerebral cortex 16
Excitability and handling of the pig 16 Object play by the pig 17
III. PERFUSION METHOD FOR PREPARING PIG BRAIN CORTEX FOR GOLGI-COX IMPREGNATION 18
A. Introduction 18 B. Procedure 18 C. Results 22 D. Discussion 23
IV. DENDRITIC GROWTH IN SOMATOSENSORY REGION OF BRAIN CORTEX IN PIGS RESIDING IN A SIMPLE OR A COMPLEX ENVIRONMENT 30
A. Introduction 30 B. Experimental Procedure 32
Animals and treatments 32 Brain preparation 34 Dendritic growth determination 34 Pig behavior 37 Statistical analysis 39
C. Results 42 D. Discussion 46
iv
ENVIRONMENTAL ENRICHMENT REDUCES EXCITABILITY IN PIGS 94
A. Introduction 94 B. Experimental Procedure 95
Experiment 1 95 Experiment II 96
C. Results 98 Experiment 1 98 Experiment II 99
0. Discussion 99
ENVIRONMENTAL EFFECTS ON EASE OF HANDLING OF PIGS. 108
A. Introduction 108 B. Experimental Procedure 108
Animals and housing 108 Treatments 109 Test apparatus 110 Test procedure 111
C. Results 113 0. Discussion 114
OBJECT INTERACTION IN WEANLING PIGS 123
A. Introduction 123 B. Experimental Procedure 125
Experiment I—short-term object preference: type 125
Experiment II—cloth object preference: texture 126
Experiment III—daily object interactions 126
Experiment IV—object interaction behavior 127
Experiment V—long-term object preference 128
Experiment VI—objects and fighting 128 C. Results 129
Experiment I—short-term object preference: type 129
Experiment II—cloth object preference: texture 130
Experiment III—daily object interactions 131
Experiment IV—relationship of object interaction and other behaviors 131
Experiment V—long-term object preference 132
Experiment VI—objects and fighting 132 0. Discussion 133
v
VIII. SUMMARY OF RESULTS AND CONCLUSIONS AND PROPOSED FUTURE RESEARCH 172
A. Summary of Results and Conclusions 172 B. General Conclusions 176 C. Future Research 180
LITERATURE CITED 181
VITA 195
vi
LIST OF TABLES
Page
Total ring intersections (TRI) and soma and TRI x soma scores in pig somatosensory cortex (trials combined) 60
Total ring intersections (TRI) and soma and TRI x soma scores in pig somatosensory cortex (trials separated) 61
Total ring intersections (TRI) and soma and TRI x soma scores in pig visual cortex (trials combined) 62
Total ring intersections (TRI) and soma and TRI x soma scores in pig visual cortex (trials separated) 63
Gender effect on total ring intersections (TRI) and soma and TRI x soma scores in pig somatosensory cortex 64
Gender effect on total ring intersections (TRI) and soma and TRI x soma scores in pig visual cortex (trials combined) 65
Gender effect on total ring intersections (TRI) and soma and TRI x soma scores in pig somatosensory cortex (trials separated) 66
Gender effect on total ring intersections (TRI) and soma and TRI x soma scores in pig visual cortex (trials separated) 67
Excitability ratings for pigs housed in enriched and nonenriched environments (Experiment I) 103
Excitability ratings for pigs reared under different environmental enrichment regimens (Experiment II, Trials 1 and 2) 104
Excitability ratings for pigs reared under different environmental enrichment regimens (Experiment II, Trial 3) 105
Weight gain of pigs reared under different environmental enrichment regimens (Experiment II, Trials 1 and 2) 106
vii
TABLE
13. Weight gains of pigs reared under different environmental enrichment procedures in Experiment II, Trial 3 107
14. Number of pigs that were electric-prodded any time during the test 117
15. Comparison of pigs that were electric-prodded any time during the test 118
16. Number of pigs which required repeated electric-prodding during the test (crowd pen and chute combined) 119
17. Number of pigs which entered the chute voluntarily 120
18. Frequencies and durations of touching and biting of objects (Experiment I) 139
19. Frequencies and durations of touching and biting of cloth objects (Experiment II) 140
20. Midpoints of periods of greatest object pulling (Experiment III) 141
viii
LIST OF FIGURES
Figure .Page
1. Schematic drawing of system used to perfuse pig brains with fixative solution 24
2. Typical Golgi-Cox-impregnated nerve cells in pig somatosensory cortex 26
3. Typical Golgi-Cox-impregnated nerve cells in pig somatosensory cortex 28
4. Location of tissue blocks in the somatosensory and visual cortex of the pig 68
5. Location of sampled neurons in the somatosensory cortex of the pig 70
6. Location of sampled neurons in the visual cortex of the pig 72
7. Layout of apparatus for testing pig behavior in Trial 1 74
8. Layout of apparatus for testing pig behavior in Trial 2 76
9. Pig pyramidal neuron that complies with the sorting criteria 78
10. Pig pyramidal neuron that complies with the sorting criteria 80
11. Pig pyramidal neuron that has a basilar tree less than 170 micrometers wide 82
12. Pig pyramidal neuron that has an asymmetrical basilar tree 84
13. Least Squares means for unsorted pyramidal neurons in the somatosensory cortex of the pig 86
14. Least Squares means for sorted pyramidal neurons in the somatosensory cortex of the pig 88
15. Least Squares means for unsorted pyramidal neurons in the visual cortex of the pig 90
16. Least Squares means for sorted pyramidal neurons in the visual cortex of the pig 92
ix
Figure
17. Layout of apparatus for testing pig handling behavior 121
18. Activity, play, and fighting patterns on the first day after regrouping (Trial 1)., 142
19. Activity, play, and fighting patterns on the sixth day after regrouping (Trial 1) 144
20. Activity, play, and fighting pattern on the first day after regrouping (Trial 2) 146
21. Activity, play, and fighting patterns on the
sixth day after regrouping (Trial 2) 148
22. Long-term object preference of pigs 150
23. Long-term object preference (Trial 1) 152
24. Long-term object preference of pigs (Trial 2) 154
25. Regression of the differences between cloth and hose pulling 156
26. Effect of cloth objects on fighting in newly regrouped pigs 158
27. Effect of cloth objects during regrouping on the number of 5-min time segments with fighting 160
28. Effect of cloth objects prior to regrouping on the number of 5-min time segments with fighting... 162
29. Effect of previous experience with cloth objects on "play" behavior in newly regrouped pigs 164
30. Effect of cloth objects prior to regrouping on the number of 5-min time segments with object interaction 166
31. Effect of previous experience with cloth objects on "play" behavior in newly regrouped pigs (5-min segments with both fighting and object interaction subtracted) 168
32. Effect of cloth objects prior to regrouping on the number of 5-min time segments with "play" (5-min time segments with both fighting and object interaction subtracted) 170
x
I. INTRODUCTION
There has been increasing societal concern about the welfare
of farm animals residing in certain modern systems which provide
less varied sensory input than natural surroundings (Harrison,
1964; Singer, 1976; Mason and Singer, 1980; Fox, 1984).
Environmental complexity affects both central nervous system
anatomical development and behavior (Bennett et al., 1964;
Diamond et al., 1964; Greenough and Chang, 1985). Barren
environments which restrict sensory input in terms of quantity,
quality, or variety tend to increase both behavioral and
central nervous system excitability. One question is: Do farm
animals residing in these systems have symptoms of sensory
restriction? Another is: Will simple, inexpensive methods of
environmental enrichment such as objects or extra contact with
people have beneficial effects on the animals' well-being? One
aim of the research reported in this thesis was to answer these
and other questions as they pertain to the pig.
A second aim was to determine if environmental enrichment
would have beneficial effects on productivity and handling
behavior. Animals which move easily during handling at the meat
packing plant will be less likely to get bruised or have stress
induced meat quality problems.
A third aim was to quantify the pig's interactions with
environmental enrichment objects and determine if environmental
enrichment would reduce fighting in newly mixed pigs.
1
II. LITERATURE REVIEW
A. Effects of Environmental Restriction and Complexity
Behavioral effects of environmental restriction
This will be a review of the scientific literature on the
effect of either isolation or sensory restriction on animals
after weaning. In all cases, prior to weaning, the animals were
reared by their natural mothers. Therefore, any effect of
sensory restriction was not confounded with the effects of
maternal deprivation, which profoundly alters later behavior
(Harlow and Zimmerman, 1959; Mason, 1960).
Isolated postweaning rearing conditions will increase the
reactivity and excitability of rodents (Korn and Moyer, 1968;
Valzelli, 1973; Riittenen et al., 1986). In the Korn and Moyer
(1968) experiments on adult rats, four weeks of isolation in
standard laboratory cages was less detrimental in these respects
than fourteen weeks. Isolation heightened emotionality; isolated
rats reacted violently when they were picked up.
Hyperexcitability has been documented in dogs kept in a
sensory-restricted environment. Pairs of puppies residing in
barren kennels become unusually aroused and excited when exposed
to something new (Melzack, 1954). These puppies could hear and
smell dogs in adjacent kennels, and the kennels were illuminated
continuously so the puppies in a pair could see and interact with
each other. Almost a year after being returned to a residential
environment with a human family, the subjects were still
2
hyperexcitable (Melzack, 1954) and electroencephalograph^
patterns from their brains indicated extreme arousal (Melzack and
Burns, 1965).
Animals living in a barren or restricted environment will
seek stimulation. During a four-hour experiment, rhesus monkeys
in an opaque cage worked hard to discriminate between blue and
yellow cards to operantly open a window for a brief glimpse into
the rest of the laboratory (Butler, 1953). Rats residing in a
barren environment will bar press more than those in an enriched
environment (Ehrlich, 1959). The restricted environment
consisted of five rats in a 60 x 30 x 23-cm wire cage. Enriched
environment rats were raised in groups of ten in a two-tiered
environment consisting of a 120 x 76 x 60-cm cage filled with
playthings such as corks, tunnels, ramps, and platforms. During
testing, each rat was placed individually in a Skinner box.
Reinforcement for bar pressing consisted of either clicks or
turning on a light.
Pigs residing in crates which were just wide enough to allow
turning around at a flared end, turned around 11 to 12 times per
day (McFarlane et al., 1988). Even animals which did not have to
turn around to gain access to feed or water nevertheless did turn
around about the same number times as did those which had to do
so. This is presumptive evidence of the pig's need for a certain
level of physical activity.
Pigs in intensive housing systems spend long periods
sleeping, punctuated by brief periods of intense excited
3
activity, as when a door slams or a person walks into the room.
This behavior is similar to that of Melzack's puppies; in the
restricted environment, they became very excited when minor
changes were made in their cages (Melzack, 1954). Stallions kept
in stalls without exercise were harder to handle than those given
daily exercise (Dinger and Noiles, 1986).
Pigs reared in indoor pens with minimal contact with people
were more excitable and difficult to load into a trailer than
those reared outside with frequent contact with people (Warriss
et al., 1983). Stolba and Wood-Gush (1980) found that pigs in
barren pens with concrete floors reacted more strongly to and
played longer with a tire than did those in straw-bedded pens.
Wood-Gush and Beilharz (1983) found that pigs in cages spent
less time lying when their environment was enriched with a trough
filled with dirt. Maybe pigs in more barren pens sleep longer to
reduce the arousal level of an overly aroused nervous system.
Zentall and Zentall (1983) suggested that autistic children
withdraw from stimulation to prevent further arousal of an
already overly aroused nervous system.
Central nervous system effects of environmental restriction
Environmental restriction has long-term effects on an animal's
central nervous system (Melzack, 1969). Six months after being
released from a sensory-restricted environment, young dogs
still had electroencephalographic patterns which indicated an
abnormally high level of arousal (Melzack and Burns, 1965).
4
The experiments reviewed in this paper support the
hypothesis put forth by Walsh and Cummins (1975) that animals
living in an enriched environment usually are less excitable than
animals in barren surroundings. Restricting sensory input makes
the nervous system of both humans and animals more sensitive and
more reactive to external stimulation. Schultz (1965) stated:
"When stimulus variation is restricted, central regulation of
threshold sensitivities will function to lower sensory
thresholds. Thus, the organism becomes increasingly sensitized
to stimulation in an attempt to restore balance." Walsh and
Cummins (1975) concluded that animals in an enriched environment
are subject to greater arousal during rearing and therefore are
less likely to exhibit overarousal in a novel or highly
stimulating environment.
Sensitization to external stimuli occurs within the central
nervous system. Placing a small cup on a person's forearm to
block tactile stimulation for one week increased tactile
sensitivity on the opposite (unshielded) forearm (Aftanas and
Zubek, 1964). This effect was quite persistent, as increased
sensitivity was still present three days after the cup had been
removed.
The sensitizing effect of restricted sensory input also can
occur across sensory modalities. The brain needs sensory input
to maintain normal reactivity levels. Zubek et al. (1964a) found
that a person who is blindfolded or wears translucent goggles for
one week has increased tactile, pain, and heat sensitivities,
5
respectively. Even partial deprivation of visual input will
sensitize the skin (Zubek et al., 1964b). Trimming the whiskers
of baby rats causes the areas of the brain that receive sensory
input from the whiskers to become more excitable (Simons and
Land, 1987), and this effect persisted. Receptive fields were
still enlarged three months after the whiskers had regrown.
Other indicators of increased central nervous system arousal
are the effects of depressant and convulsive drugs, respectively,
on animals residing in different environments. Rats living
singly in small cages were compared to those in groups, and the
isolated rats had higher thresholds for anesthetics. Juraska et
al. (1983) administered both depressant and convulsive drugs to
rats isolated in small laboratory cages (isolated condition, IC)
or living in a group of 12 in an enriched environment (enriched
condition, EC) which consisted of a large enclosure with many
different toys. The IC rats injected with sodium pentobarbital
took longer to lose the righting reflex. In a second experiment,
when rats reared in IC and EC, respectively, were given the
convulsant drug, pentylenetetrazol, the IC rats went into light
flash-induced convulsions at lower doses.
Bombarding an animal with excessive stimulation can cause
detrimental signs similar to those caused by restricted
stimulation. In the IC/overstimulated condition, mice were
subjected involuntarily to intense sound, light, and vibration,
whereas those in the EC were allowed to initiate and control
their interaction with toys. Both IC and IC/overstimulated mice
6
were more irritable than were EC mice, and both forced
understimulation and forced overstimulation increased
irritability.
Concept of optimal stimulation
Zentall and Zentall (1983) believe that organisms modulate
incoming sensory stimulation to maintain the nervous system at an
optimal level of arousal. In some cases, for example,
stereotyped behavior may be an attempt by a disturbed biological
system to restore homeostasis (Damasio and Maurer, 1978).
Environments offering low levels of stimulation tend to cause
behavior in animals which is stimulus-seeking. Conversely,
animals living in an overstimulating environment sometimes
attempt to reduce their central nervous system arousal by
engaging in repetitive activity (Zentall and Zentall, 1983).
Dantzer and Mormede (1983) and Dantzer (1986) suggested that
repetitive stereotypic behavior can serve a de-arousal function.
For example, food-deprived pigs will engage in repeated chain-
pulling in between food deliveries which occurred every four
minutes, and pigs which had access to the chain had lower plasma
corticosteroid levels. Stereotypies also occur in pigs living in
barren environments which provide low levels of sensory
stimulation (Ewbank, 1978; Markowitz, 1982). Therefore,
stereotypies may occur in both understimulating and
overstimulating environments. In understimulating environments,
of course, they probably serve to increase sensory input (Ewbank,
1978; Markowitz, 1982). Young children deprived of normal
7
hugging will engage in excessive masturbation, which stopped when
nonsexual tactile contact with parents was increased (McGray,
1978).
Even though animals living in a barren environment may
attempt to reduce central nervous system arousal level, the
central nervous system nevertheless may remain in an abnormally
aroused state. Perhaps some of the environments that have been
imposed experimentally deprived the animals beyond their
physiological ability to cope. For example, extremely barren
environments would never be encountered in nature.
Nervous systems are endowed with a certain amount of
plasticity so the animals can deal with changing environmental
demands. The ability to adjust the relative "sensitivity" of
sensory systems to different environments would be useful to an
animal for survival in the wild. Simons and Land (1987)
concluded that sensory input affects the development of the
brain's somatosensory cortex.
Structural changes in the brain
Stimulation and opportunities for activity provided by an
enriched environment cause changes in dendritic branching in the
brain. Groups of weanling rats residing for four weeks in a
large enclosure with toys and objects to climb (enriched
condition, EC) had greater dendritic branching in the visual
cortex than did those living singly in standard laboratory cages
(isolated condition, IC) (Greenough and Juraska, 1979; Volkmar
and Greenough 1972).
8
More recent research results indicate that new synapses may
be formed by neural activity induced by the enriched environment
(Greenough et al., 1985). Researchers also have compared IC and
EC with (social condition, SO), the latter consisting of two
animals living together in a 22 x 25 x 30-cm laboratory cage.
Fleeter and Greenough (1979) found no differences in dendritic
branching in the cerebellums of SO and IC monkeys (Macaca
fascicularis). The EC monkeys had the most dendritic branching.
In rats, SC animals had intermediate levels of dendritic
branching in the visual cortex (Volkmar and Greenough, 1972).
The IC rats had the least branching, the EC rats the most.
Weanlingrats in EC also had heavier brains than did those in IC
(Bennett et al., 1964; Diamond et al., 1964). Rats in EC also
had a thicker cortex and additional glial cells (Bennett et al.,
1964; Diamond et al., 1964; Diamond, et al., 1966). In these
experiments, the control rats were housed in trios in 32 x 32 x
20-cm laboratory cages, and all rats were in their respective
environments for at least 29 days.
Very short (four-day) periods of differential housing
affected cortical depth in the dorsal-medial part of the brain's
occipital cortex (Diamond et al., 1976). Cortical depth
differences in weanling rats were induced mainly by environmental
impoverishment, whereas in adults they were induced mainly by
enrichment.
Neural hypertrophy does not necessarily mean that an animal
is in an environment that is higher quality overall. Research
9
indicates that neural hyptertrophy can sometimes be detrimental.
Rats exposed to continuous lighting had greater spine density in
the visual cortex (Parnavelas et al., 1973), but their retinas
were damaged (Bennett et al., 1972, O'Steen, 1970). Stimulation
of the hippocampus with an implanted electrode induced axonal
growth and reorganization of synapses, but these new connections
increased excitability and seizures developed (Sutala et al.,
1988)
Farm animals
Enriching pigs' environments may help prevent changes in the
central nervous system which lead to hyperexcitability and
stereotyped behavior. Casual observations of pigs residing in
indoor pens indicates that they often exhibit an excessive
startle reaction to door slamming or other disturbances.
Farmers have learned that playing a radio with a variety of music
and talk reduces pigs' reactivity to extraneous sounds.
Observations at slaughter plants indicate that some pigs are more
excitable and difficult to handle than others (Grandin, 1986).
Pigs living in indoor pens with minimal contact with people
were more excitable and difficult to load than those residing
outside with frequent contact with people (Warris et al., 1983).
Pigs from 1.2 x 1.2-m relatively barren pens also were slower to
approach a novel object or human strangers compared to pigs that
had had access to toys and frequent contact with people (Grandin
et al., 1983).
10
Pigs which are either balky or excitable are more difficult
to transport and handle at the slaughter plant. Those that are
reluctant or refuse to move are more likely to be subjected to
excessive electric-prodding. Electric prod-induced excitement is
detrimental to pork quality (Barton-Gade, 1985; Grandin, 1986).
Repeated electric-prodding also will increase bloodsplashing
(hemorrhage) in the pork carcass (Calkins et al., 1980).
Further, it is detrimental to the pig's welfare; heart rate
increases progressively with successive prods, and if it is
continued, the pig's heart rate will reach dangerously high
levels and death can result (van Putten and Elshof, 1978; Mayes
and Jesse, 1980). A pig will stop and lie down when its heart
rate is near the lethal point (Mayes and Jesse, 1980).
B. Environmental Enrichment Methods
Choice of envi ronmental enrichment
Stolba (1981) observed pigs in a semi-natural environment to
help determine suitable environmental enrichment devices. Their
studies were an important first step in determining choices pigs
make from among a variety of natural objects. It is important
that the play objects provided pigs be things that they
appreciate, and the objects must support sustained interest.
Research can be used to determine the type of objects pigs
prefer.
Choice tests have been used to determine animals'
preferences for type of flooring, social groupmates, and mate
11
(Hughes and Black, 1973; Hughes, 1976; Dawkins, 1982; Farmer and
Christisdn, 1982; McGlone and Morrow, 1987); to test sheep's
preferences for type of handling facilities (Hitchcock and
Hutson, 1979; Hutson, 1981) and restraint methods (Grandin et
al., 1986; Rushen, 1986); and to determine pigs' preferred angle
and flooring surface for ramps (Phillips et al., 1988).
When choice tests are used, it is essential that they be
controlled adequately to prevent previous experiences from
influencing the choices. For example, previous experience with
different pastures can alter pasture preference in sheep (Arnold
and Mailer, 1977), and the environment in which they were reared
can affect caged hens' subsequent flooring and social preferences
(Hughes, 1976).
Another potential problem with preference tests is that
something that is preferred on a short-term basis may have
detrimental long-term effects on the animal's well-being (Hughes
and Black, 1973; Duncan, 1978; van Rooijen, 1982). For example,
animals may prefer one type of flooring during a two-hour
preference test, but the preferred flooring may injure the
animals' feet after several months.
Piglets usually prefer plastic-coated expanded-metal floor
over concrete (Farmer and Christison, 1982). In practice,
plastic-coated expanded-metal flooring is excellent for farrowing
crates and nursery pens but causes problems when used for a
finishing floor. Casual observations indicated that pigs
finished on either flattened or plastic-coated expanded metal had
12
excessive hoof growth, and they balked and were difficult to
drive into a high-speed slaughter line (Grandin, 1988).
Preference tests are one useful method for determining
practical objects that producers could use to enrich a pig's
environment. Unlike flooring, feed, or housing, object choices
are unlikely to have adverse long-term effects on the pigs'
health or performance. There is a need for information on the
pig's short- and long-term preferences for means of environmental
enrichment so that recommendations can be made to producers.
Plav in Farm Animals
Farmers have offered pigs various objects in attempts to
enrich their environment and reduce vices, van Putten (1969)
recommended placing chains or rubber hoses in pens to occupy the
pigs' attention and reduce tail-biting. Weanling pigs will play
with many kinds of objects, and they vigorously chewed, tugged,
and shook suspended strips of cotton cloth (Grandin et al.,
1983). They also rooted and rolled balls, wooden boards, plastic
boxes and other objects when these items were first placed in.
their pen. When these objects became soiled with excreta,
however, the pigs lost interest in them. Suspended strips of
cloth seemed to hold the pigs' interest longer than did suspended
chains, clean objects more than did soiled.
Fagen (1984) described play as follows: "Play means
behavioral performance that emphasizes skills for interacting
with the physical and social environments and that occur under
circumstances under which the function of the exercised skills
13
can not possibly be achieved." Play occurs in many farm animals,
including cattle, sheep, pigs, and horses (Brownlee, 1954, 1984;
Tyler, 1972; Schoen et al., 1976; Sachs and Harris, 1978; van
Putten, 1978; Dobao et al., 1984-85; Crowell-Davis et al., 1987),
as well as a relative of the domestic pig, the collared peccary
(Byers and Beckoff, 1981; Byers, 1984). It is interesting that
in the collared peccary both juveniles and adults play, because
ordinarily in ungulates only juveniles and subadult males play
(Byers, 1984).
Object play, including "tug-of-war", has been observed in
dogs, cats, horses, and jackals (van Lawick and Goodall, 1971;
West, 1977; Fagen, 1981; Martin, 1984). Captive bushdogs and
foxes play with sticks (Biben, 1982). A captive rhinoceros will
root a ball and other objects (Inhelder, 1978; Hediger, 1968).
Piglets also engage in object play (Gundlach, 1968; Fraedrich,
1974). Weanling pigs tugged on cloth strips in a manner similar
to that of dogs playing "tug-of-war" (Grandin et al., 1983).
Foals will pick up sticks and carry them around and toss them in
the air (Crowell-Davis et al., 1987).
Activity patterns in livestock
There are few data available on the daily activity patterns
of play in pigs. Domestic livestock do have daily patterns of
activity for grazing and other behavior (Hughes and Reid, 1951;
Squires, 1974; Arnold and Dudzindki, 1978). Pigs residing
indoors are more active during the day (Morrison et al., 1968).
In rich environments there are two peaks of activity—around 0900
14
and 1700 hrs in pigs (Dantzer and Mailha, 1972; Dantzer, 1973;
Bure, 1981). When pigs had an opportunity to control the
temperature in their pen, a cooler environment was preferred at
night (Curtis and Morris, 1982).
Aggression and envi ronmental enrichment
Pigs are a relatively feisty species. When strange pigs are
mixed they will fight one another vigorously, at least in part to
establish a new social order (McBride et al., 1964). Fighting
among pigs causes injuries (Symoens and van der Brand, 1969;
Jones, 1969) and will reduce weight gains if the pigs are
overcrowded or have limited access to food (Graves et al.,
1978; Sherritt et al., 1974).
Fighting among newly weaned piglets generally has little
adverse effect on the pigs' long-term performance, but it can be
detrimental to welfare. McGlone and Curtis (1985) found that
fighting and injuries could be reduced by providing newly weaned
pigs small hides where they could place their head and shoulders.
Anecdotal reports suggest that providing pigs toys during times
of social mixing also will reduce fighting.
Straw bedding did not reduce fighting in growing pigs fed ad
libitum, but it had a tendency to reduce fighting in fasted pigs
(Kelley et al., 1980). Another factor which will influence
aggression is type of housing. Pigs in indoor pens were more
aggressive than those residing outdoors (Meese and Ewbank, 1973).
Crowding tends to increase pig aggression (Bryant and Ewbank,
1972; Kelley et al., 1980; Randolph et al., 1981), but it does
• 15
not increase all kinds of aggression in a uniform manner.
Reducing floor space reduces aggression which occurs away from
the feeder, but it has no clear effect on aggression at the
feeder (Ewbank and Bryant, 1972). Restricting lying space
increased aggressive encounters when animals were standing but
had little effect on aggression in other areas (Ewbank and
Bryant, 1972). More information is needed about the effects of
environmental richness on aggression in pigs.
C. Thesis Research Outline
Dendritic growth in the pig's cerebral cortex
In the first experiment to be reported in this thesis, the
effect of environmental enrichment on dendritic growth in the
pig's brain was studied. Heretofore, many such studies have been
conducted with rodents (see review by Greenough and Chang, 1985),
and three with primates (Struble and Riesen, 1978; Fleeter and
Greenough, 1979; Stell and Riesen, 1987). The study to be
reported here was the first conducted with a domestic farm
animal. Valuable knowledge about environmental effects on brain
development may be able to be gained by studying animals that
have a larger, more complex brain than does the rat.
Excitability and handling of the fiig.
The second series of experiments were designed to determine
effects of environmental enrichment on the excitability and
handling of pigs living in intensive systems. The aim was to
determine effects of various kinds and extents of environmental
16
enrichment on the excitability of pigs in space-restrictive,
relatively barren pens.
Object play by. the pig
In the third series of experiments, choice tests were
conducted to determine the types of play objects that are
preferred by pigs, both short- and long-term. Daily activity
patterns of toy play also were determined. In the last
experiment, effects of access to play objects prior to or
during social mixing of newly weaned piglets were determined to
learn whether toys would reduce agonistic behavior.
The environmental enrichment methods used in all of these
experiments were simple, practical procedures that swine
producers could use. Results of these experiments may help
answer questions as to whether relatively simple environmental
enrichment procedures will improve the productivity and welfare
of pigs residing in intensive production systems.
17
III. PERFUSION METHOD FOR PREPARING PIG BRAIN CORTEX
FOR GOLGI-COX IMPREGNATION
A. Introduction
The development of Golgi-Cox staining procedures for pig
brain was required because existing methods of fixing and
preparing brain tissue that worked well with rodent or primate
tissue (Glaser and Van der Loos, 1981; Fleeter and Greenough,
1979; Green et al., 1983; Greenough 1984) gave poor results with
tissue from both visual and somatosensory cortex of pigs; fresh
tissue immersed directly in Golgi-Cox solution showed incomplete
neuron impregnation, and the same tissue fixed first in 10%
buffered formalin showed poor neuron and excessive glia staining.
Before the experiments could proceed, a new method of perfusion
and fixation of the pig brain was developed.
B. Procedure
Six or twelve 45-kg Hampshire-sired crossbred pigs (Sus
scrofa) were used on each of three occasions. At an abattoir,
the pigs were killed by exsanguination within 30 sec after having
been stunned electrically. Within 1 min after death, the pig's
entire head was removed and to prevent autolysis placed in a
bucket of ice for transport to the laboratory. (To facilitate
later location of the carotid arteries and their connection to
the perfusion apparatus, an additional 4 to 6 cm of neck was left
on the head; ordinarily the neck is transected immediately behind
18
the pinnae.) Each head remained packed in ice up to 30 min
before starting perfusion with fixative.
Upon removing a head from the ice, both of its carotid
arteries were connected to an air pump perfusion system operated
at a pressure equivalent to 70 mm Hg. The system was a high-
capacity unit used to embalm large animals to be dissected by
students. Heads were perfused for 4 hr on the day of slaughter
and for an additional 4 hr the following day. The arteries were
connected to the system by insertion of a flexible plastic
catheter (2-mm-OD, 1.5-mm-ID) 1.5 cm into each artery, where it
was secured by a string ligature. Hypodermic needles (16 gauge)
were inserted into the free ends of the catheters, then the
needle hubs were inserted into short lengths of rubber tubing
(12-mm-OD, 8-mm-ID) which in turn were connected to an
appropriately sized plastic Y-tube (Nalgene #6153). The stem of
the Y-tube was then inserted into a short length of rubber tubing
(12-mm-OD, 8-mm-ID) which led to the stem of a second Y-tube
(Figure 1). One arm of the second Y from the first head was
connected directly to the pump, while the other arm was connected
to the stem of the second Y from the second head, and so on. Six
or twelve heads were perfused simultaneously in parallel by the
one system.
The perfusion fluid was a fixative solution composed (v/v)
of liquid phenol, 5%; formalin, 14%; ethylene glycol, 25%;
methanol, 28%; and water, 28%. The heads were perfused at room
temperature (~22° C).
19
When the perfusion had been completed, the pig heads were
placed in a walk-in cooler (2° C) for 18 hr. Brains were removed
from the skull in one piece by carefully cutting the skull away
with a bone saw and a hammer and wood chisel. The intact brain
was placed immediately in 500 ml 10% buffered formalin for at
least 10 days prior to Golgi-Cox impregnation.
The Golgi-Cox solution was prepared from three stock
solutions, producing the solution specified by Glaser and Van der
Loos (1981)—stock solution 1: 37.5 g K2Cr207 in 750 ml
deionized water warmed to 30° C during mixing with a magnetic
stirrer; stock solution 2: 37.5 g HgCl2 in 750 ml deionized
water heated to 95° C during mixing with a magnetic stirrer; and
stock solution 3: 30 g K2Cr04 in 600-ml cold deionized water
(Greenough, 1982). Stock solutions 1 and 2 were mixed and then
added to stock solution 3 just after the latter had been diluted
with deionized water to a final volume of 1500 ml. A brown glass
bottle was used to shield the final Golgi-Cox solution from
light. The mixed solution was allowed to stand for 3 days to
allow particulate matter to settle; the supernate was decanted
and filtered through Whatman No. 42 paper (Greenough, 1984).
Blocks of tissue approximately 4 mm x 10 mm x 10 mm were cut
from each brain's visual and somatosensory cortex (Adrian, 1943;
Kruska, 1972). Each tissue block was wrapped in clean gauze and
immersed in 150-ml Golgi-Cox solution. After 24 hr, both Golgi-
Cox solution and gauze were changed. The containers with the
20
tissue blocks were kept in the dark for three weeks, the minimum
time required for uniform staining.
Before embedding, a test section was developed in ammonia
water (19% NH40H) and examined under a microscope to determine
whether the impregnation was complete. If impregnation was
incomplete, the tissue block was reimmersed in the Golgi-Cox
solution for another week.
After being impregnated, the tissue was dehydrated through
1:1 ethanol:acetone for 3 hr, 100% ethanol for 20 min, and 1:1
anhydrous diethyl ether:100% ethanol for 20 min. Six and twelve
percent celloidin solutions were prepared by dissolving Parlodian
strips in 1:1 anhydrous diethyl ether:100% ethanol. Each tissue
block was placed in 6% celloidin for 6 days and then in 12%
celloidin for 6 days. The celloidin-impregnated tissue was
hardened over chloroform in a desiccator and mounted on a wooden
block.
After mounting, the blocks were stored under butanol until
sectioned at 120 urn using a sliding microtome (thick sections are
required to prevent excessive transecting of radially oriented
dendrites). The sections were processed in the following manner
(Glaser and Van der Loos, 1981): 1) 70% ethanol for 10 sec, 2)
50% ethanol for 10 sec, 3) deionized water for 30 sec, 4) ammonia
water (19% NH40H) for 20 min, 5) deionized water for two 30-sec
immersions in separate pans, 6) fixer (Kodak Rapid Fix diluted
1:7) for 10 min, 7) deionized water for two 30-sec immersions in
separate pans, 8) 50% ethanol for 10 sec, 9) 70% ethanol for 10
21
sec, 10) 95% ethanol for 60 sec, and 11) 100% ethanol for two 20-
sec immersions in separate pans.
To facilitate handling, each tissue section was placed in a
compartment of a perforated plastic ice cube tray (Greenough,
1984). The 100% ethanol was changed after two ice trays had been
processed (water contamination of the final dehydration step will
ruin the sections). Trays containing the sections were blotted
on paper towels after every step. Immediately after dehydration,
the sections were placed under xylene and rapidly mounted on
glass slides using Permount. To prevent curling of the sections,
a 100-g paraffin-coated lead weight was placed over the glass
cover slip and the slides were allowed to dry for 3 weeks. The
relatively thick sections required this much drying time to
ensure stability of the covers!ip during cleaning and use.
C. Results
The procedure described in this paper produced high-quality
Golgi-Cox-impregnated neurons from both the visual and the
somatosensory cortical regions of pig brain (Figures 2 and 3).
Pig brains that had been immersed in 10% buffered formalin
solution for 5 wk after perfusion with a special fixative
solution and before impregnation yielded even higher quality
impregnated neurons that did those kept in the formalin for only
10 days.
The procedure described in this paper produced poor quality
Golgi-Cox-impregnated sections from pig cerebellar cortex. The
22
cerebellum appeared to be adequately perfused, but impregnation
quality was poor.
Pig heads perfused in groups of six were fixed more
uniformly than were those perfused in a group of twelve.
0. Discussion
The perfusion fluid used for this procedure was the
traditional one used to embalm animals to be dissected by
students. The discovery that it was effective in fixing pig
brain cortex for Golgi-Cox impregnation was serendipitous.
Perfusing more than six heads with the perfusion apparatus
we used would not be recommended. It is likely that heads in
excess of six exceeded the capacity of the pump; there did not
appear to be a tendency for heads closer to the pump than the
sixth one to be perfused more uniformly than that one.
There are two advantages of perfusing isolated pig heads as
opposed to perfusing the whole body; less perfusion fluid is used
and the rest of the carcass can be salvaged.
23
Figure 1. Schematic drawing of system used to perfuse pig brains
with fixative solution.
24
Rubber Hose Connector Plastic Catheter
Carotid Arteries Tied with String to Hold Catheter In Place
Rubber Hose
Hose to Next Head
ose to Pump System
Second Plastic Y HtJing
25
Figure 2: Typical Golgi-Cox-impregnated nerve cells in pig
somatosensory cortex, x 275. Fine structural
details, such as spines, appear clearly impregnated,
whereas background staining of glial tissue varies
across laminar section.
26
27
Figure 3. Typical Golgi-Cox-impregnated nerve calls in pig
somatosensory cortex, x 1500.
28
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29
IV. DENDRITIC GROWTH IN SOMATOSENSORY REGION OF BRAIN CORTEX
IN PIGS RESIDING IN A SIMPLE OR A COMPLEX ENVIRONMENT
A. Introduction
An animal's experiences affect the anatomical development
of its brain. Volkmar and Greenough (1972) studied weanling
rats that had resided for 29 or 30 days in three different
environments:enriched condition (EC), social condition (SC),
and isolated condition (IC). In the EC, 12 animals resided
most of the time in a 45 x 60 x 70-cm cage furnished with many
different objects that were changed daily, and they also were
placed in a large object-filled box for 30 minutes of activity
every day. The objects were pieces of wood, children's toys,
ladders, and laboratory utensils. In the IC, single rats
resided in 22 x 25 x 30-cm cages with solid metal sides and a
wire mesh top and front. In the SC, the rats resided in pairs
in the same type of cage as in the IC. Rats in the EC group
had the most dendritic branching, those in the IC the least.
Differential rearing environment had the greatest effect on the
higher-order dendrites (i.e., those located farther from the
cell body).
Similar but smaller and more localized increases in
dendritic branching have been found to occur following training
in mazes and motor tasks (Black et al., 1987; Chang and
Greenough, 1982; Greenough et al., 1985).
30
Most studies on the effects of environmental richness on
dendritic branching and synapse growth have been conducted on
rodents (Greenough and Chang, 1985). The EC/SC/IC paradigm
described above was used in a monkey study, too (Fleeter and
Greenough, 1979). Macaca fascicularis raised in the EC (with
toys and climbing structures) had more dendritic branching in
cerebellar Purkinje cells than did paired or isolated monkeys.
The EC monkeys also had larger Purkinje somas.
In another experiment, old World monkeys (Macaca arctoides)
placed in isolation had significantly less dendritic branching
than colony-reared monkeys (Struble and Riesen, 1978). Further
studies by Stell and Riesen (1987) indicated that monkeys reared
in isolation with objects, ladders, and swings had greater
dendritic branching in the motor 1 cortex compared to monkeys
reared by their mothers in the colony or reared in isolation
without gymnastic equipment.
In cats, Spinelli et al. (1980) found that training a kitten
to avoid a shock by lifting its foreleg resulted in greater
dendritic density in the cortical area which receives sensory
input from the forearm. Beaulier and Colonnier (1987) also found
that IC cats had more FS synapses and fewer RA synapses per
neuron compared to EC cats. FS and RA synapses are the two main
morphological types of synapses in the cerebral cortex. FS
synapses have flat vesicles and RA synapses have round vesicles.
The preceding experiments have all involved conditions
specifically designed for comparison of environmental enrichment
31
or training with its absence. The purpose of the present
experiment was to determine whether the quality of different
rearing environments which might be used in production
agriculture can affect the morphology of cerebral cortical
neurons in pigs. To assess this, pigs reared in a simple,
production-like condition were compared with pigs reared in a
large group with straw, a variety of different objects, and
additional contact with people.
B. Experimental Procedure
Animals and treatments
Twenty-four littermate pairs of 18- to 25-day-old Hampshire-
sired crossbred pigs were studied in two trials. Mean weight
of trial 1 pigs was 7.97 kg (SD=0.87) and trial 2 pigs was
10.78 kg (SD=1.60). In each trial, 12 pigs resided in a
complex environment (CE) (similar to the EC in the experiments
described earlier), and 12 in a simple environment (SE)
(similar to the SC described earlier). Trial 1 lasted 68 days,
and Trial 2, 65 days. Half of the animals in each trial were
used for anatomical study.
The SE consisted of rearing two pigs in each of six 1.22 x
1.22-m pens with plastic-coated expanded-metal floors in a
windowless, environmentally controlled house where air
temperature was 22 to 26 C. Pen partitions were constructed of
vertical glass fiber-reinforced plastic rods. Pigs in
different pens could see each other, but could have no physical
32
contact, because there was an empty pen between every two that
were occupied. The room was illuminated continuously by
fluorescent tubes (200 lux) in Trial 1. In Trial 2, the
luminal res were timer-controlled so illumination started at the
approximate time of sunrise (0600) and stopped at the
approximate time of sunset (2030) each day; this provided the
SE pigs with approximately the same light/dark cycle as the CE
pigs. The SE pigs ate from a self-feeder and drank from a
nipple waterer. The room was entered only for feeder servicing
for 10 min every day or pen washing for 60 to 90 min every
third day.
The 12 CE pigs resided together in a house with a concrete
slab floor bedded with straw (new straw added daily) with an
adjoining outdoor pen with a concrete slab floor. In both
trials, the CE pigs were handled by the experimenter for 15 to 30
min every day. The experimenter petted the animals, scratched
their abdomens, and allowed them to chew on boots and coveralls.
In Trial 1, the CE pigs were provided a variety of objects
to manipulate. These objects were changed daily and included a
plastic milk crate, various cloth strips tied to the fence,
ropes, chains, plastic ball, dirt, corrugated cardboard,
newspapers, telephone directories, soda cans, stones, garbage
can, and pieces of wood. The CE pigs in Trial 2 were provided
only three 7.5 x 50-cm white cotton cloth strips suspended from
a rope across the pen; the strips were changed weekly. Feed
33
was provided in a self-feeder with lids, and water was provided
in a float-controlled automatic waterer.
Brain preparation
At the end of each trial, six pigs from each treatment group
were sacrificed and their brains were perfused, fixed, Golgi-Cox
impregnated, sectioned, and mounted by procedures described in
Chapter III (Grandin et al., 1988), a modification of the
methods of Glaser and Van Der Loos (1981) and Greenough (1984).
Figure 4 shows the locations of the tissue blocks that were
removed from the visual and somatosensory regions of the
cerebral cortex. Somatosensory cortical tissue blocks were
from the area determined by Adrian (1943), who used evoked
responses to tactile stimuli from the brain of anesthetized
pigs. Adrian (1943) and Woolsey and Fairman (1946) are in
excellent agreement in this regard. The work of Kruska (1971,
1972) was used to determine the location of the visual cortex
in the pig brain. Results of Campbell (1905) are in accord
with Kruska's findings.
Dendritic growth determination
An Olympus BH-2 binocular microscope (Tokyo, Japan) with
an Olympus BH2-DA camera lucida attachment was used to make
pencil tracings of layer II pyramidal cells in both the
somatosensory and visual regions of the cerebral cortex. All
slides were coded so the drawings could be made with the drawer
blind to treatment. Microscope magnification was 450X.
34
To determine the level of cortical lamination, 12 visual
cortex sections of each brain were counterstained with
methylene blue following the Glaser and Van Der Loos (1981)
protocol (counterstained sections were not used for data
collection). The processing procedure was the same as
described in Chapter III, but additional steps were added after
sectioning:
1. 70% ethanol for 10 sec
2. 50% ethanol for 10 sec
3. Two immersions in deionized water in separate pans
for 30 sec each
4. Ammonia water (19% NH40H) for 20 min
5. p-Phenylene di-amine (.5 g in 1000 ml water) for 5 min
6. Two immersions in deionized water in separate pans
for 2 min each
7. 1% Kodak Dektol Fixer for 2 min
8. Kodak Rapid Fixer for 7 min
9. Three immersions in deionized water in separate pans
for 5 min each
10. 1:1 tamponee:water for 5 min (formula for tamponee:
sodium acetate 13.6 g, glacial acetic acid 23.45
ml, water to make 1 L)
11. 1:1 and 2% methylene blue in deionized water
for 8.5 min.
12. Tamponee for 30 sec
13. 1:1 tamponee and deionized water for 20 min
35
14. 50% ethanol in deionized water for 15 sec
15. 70% ethanol in deionized water for 15 sec
16. 95% ethanol in deionized water for 60 sec
17. Two immersions in 100% ethanol in separate pans for
20 sec each.
For each pig, a minimum of 14 drawings of basilar dendrites
of layer II pyramidal neurons in the visual and somatosensory
regions of the cerebral cortex, respectively, were made at 450X
magnification. Apical dendrites were not evaluated because many
of them had been transected by the microtome. Pig cortical
neurons are extremely large relative to those of rodents, and
therefore more difficult to align.
A stratified sampling method was developed to specify the
location of the pyramidal cells to be drawn. The outline of
each section was traced with a projection microscope (Bausch
and Lomb 42-63-59, Rochester, New York) at low power (22X).
Lines were drawn connecting landmarks on the projected drawing
(as shown in Figures 5 and 6) to determine three locations in
the somatosensory cortex and four in the visual cortex. More
than one location was used because usually there were an
insufficient number of well-impregnated or untransected cells
in any one location. In the somatosensory cortex, four
drawings were made from each location, and in the visual
cortex, three. Four sections per animal were used. The
remaining two drawings of the 14 were made from two locations
picked at random (if remaining undrawn neurons in the
36
respective areas were well-impregnated) or from the undrawn
well-impregnated neurons which remained in the locations.
Dendritic complexity was quantified by concentric ring
analysis (Sholl, 1956; Greenough, 1975). A clear plastic overlay
with concentric circles at 20 m equivalent intervals was
centered visually over the neuron's soma, and the basilar
dendritic branches that crossed each ring were counted. Total
ring intersections (TRI) were then determined by summing the
counts for all rings.
Soma width was determined by measuring the width of the cell
body at its widest point, 90 degrees perpendicular to the main
apical process. Measurements were made on the camera lucida
drawings with a ruler marked at millimeter intervals.
Pig behavior
At the end of Trial 1, behavior of pigs from both
environments was tested to determine the pig's time to approach
a strange man and a novel object, respectively. Each animal
was tested individually in an octagonal arena with 1.22-m-high
white-painted plywood walls (Figure 7). The arena floor was
covered with brown plastic carpet. The vestibule floor was
broom finish concrete. The room was illuminated at 200 lux.
Tests of time to approach the strange man and time to approach
the novel object were conducted separately. The strange man
was a person unknown to the pigs. He stood still during the
test. The novel object was a new red metal feeder, standing on
its end.
37
Testing was alternated between CE and SE pigs. Strange-
man approach tests and strange object approach tests were
conducted successively, in random order. During testing, each
pig was placed in the vestibule for a 3 min adjustment period.
After this, the entrance gate to the arena was opened. The
timer was started when the pig's nose passed the entrance gate
and stopped when the pig walked up and touched the man or the
object. The test was terminated if the pig failed to touch the
man or the object within 3 min.
At the end of Trial 2, behavior of pigs from both
environments was tested in a narrow chute. The layout of the
apparatus is shown in Figure 8. The narrow chute was constructed
from plywood painted white. It was 1.22-m high, 27-cm wide at
the bottom and 38-cm wide at the top. The wooden chute floor was
painted gray and the vestibule floor was covered with brown
plastic carpet.
To tend to discourage the pig's movement through the
chute, the floor contained three obstacles perpendicular across
the path: a 5-cm-wide light beam, a 7.5-cm-wide perforated
metal strip, and a 2 x 3.7-cm-wide wood board. To encourage
movement through the chute, a decoy pig (not from the
experiment) was placed in a welded-wire mesh pen at the end of
the chute.
The testing procedure was similar to that in Trial 1
except there was no adjustment period in the vestibule. The
timer was started when the pig was placed in the vestibule.
38
The test was terminated if the pig failed to walk all the way
through the chute to the decoy pig within 5 min. Each pig was
tested twice.
In Trial 2, behavior of pigs in both environments was
observed for 24 h during week 7 of the trial. It was
videorecorded (NV8030 time-lapse recorder, Panasonic Co.,
Secaucus, NJ). The videorecording system was operated at 0.9
frames/s. In the SE, one camera viewed three of the six pens.
In the CE, one camera viewed the inside of the straw-bedded shed,
and a second the concrete slab. Data were registered while
records were reviewed at a speed 18 times faster than the
recording speed. High-speed reviewing made subtle nosing and
rooting movements appear as readily discernible vibrations of the
snout. Nosing of other pigs and rooting or chewing objects was
quantified by one-zero sampling (Lehner, 1979) every 5 min.
The entire videorecord was viewed. A five-min interval, in
which one pig was active in the way of interest, was given a
score of 1; if two different animals were observed to be active
within the same interval, a score of 2 was given, and so on.
Statistical analysis
The individual pig was the experimental unit. The
dependent variables were total ring intersections (TRI), soma
width, and the product index, (TRI x soma width). The latter
variable was calculated to serve as an index of neuron
development.
39
Data were analyzed by the SAS General Linear Model (analysis
of variance) procedure (SAS, 1982). In an attempt to enhance the
power of the statistical tests, individual data (x) were
transformed as follows: x2, log x, arcsine Vx7 "Vx", and (x -
1). The ^transformed data improved the significance level, and
data resulting from this transformation will be presented and
interpreted together with the raw data.
While camera lucida drawings were being made, it became
apparent that many pyramidal cells had a distorted shape.
Apical dendrites were twisted, and some basilar trees were
grossly asymmetrical. In some cases, the asymmetry was not due
to transection by the section plane. Instead, it was the
natural shape of the cell. To determine if distortion of the
cells was affecting our ability to detect differences in
dendritic growth due to environment, a sorting procedure
suggested by Janice M. Juraska (personal communication, 1987)
was developed to arbitrarily eliminate distorted cells. In the
end, pyramidal cells had to comply with the following criteria
to be retained in the sorted category:
1. Basilar tree more than 170 m in diameter measured
perpendicularly relative to the apical process (9 mm
measured on the camera lucida drawing was equal to
20 m on the cell).
2. Soma more than 18 m wide at the widest part
perpendicular to the apical process.
40
3. Symmetrical basilar tree. (If more than 75% of the
basilar dendrites were on one side of a line extending
180 degrees from the apical process, the cell was
rejected.)
4. Main apical branch more than 140 m long. (If the
main apical process was transected, but more than
4 m wide at the point of transection, the cell was
retained. This criterion was based on experience
studying pyramidal cells. Cells with apical
processes 4.5 m or thicker near the soma had
apical processes and dendrites longer than 140 m.)
These criteria were arbitrary, but they were based on
experience and intended to remove the misshapen cells and cells
that did not conform to the symmetrical pyramidal cells with
long apical processes described in several reports (Sholl,
1956; Greenough, 1975; Greenough and Juraska, 1979). Figures 9
and 10 illustrate somatosensory layer II pyramidal neurons
which satisfy the above criteria, whereas Figures 11 and 12
illustrate neurons that do not satisfy these criteria. The
basilar tree is less than 170 m wide in Figure 11, and in
Figure 12 the basilar tree is asymmetrical. Basilar trees with
a major branch transection near the cell body were also
rejected. In Trial 1, 9.91 (SD=4.50) somatosensory cortical
drawings per pig were retained in the sorted data set; in Trial
2, 7.50 (SD=1.45). In Trial 1, 5.27 (SD=1.11) visual cortical
41
drawings per pig were retained; in Trial 2, 6.66 (SD=2.39).
Data for both sorted and unsorted cell sets were analyzed.
Visual cortical data for one CE barrow in Trial 1 was
unavailable for analysis due to incomplete Golgi-Cox
impregnation.
C. Results
Pigs reared in the SE had more extensive basilar dendrites
in the somatosensory cortex than did those in the CE. Total ring
intersections for both trials combined (unsorted) were 55.70 +
2.38 (mean + SE) in SE pigs and 48.62 + 2.38 in CE pigs (P<.06;
Table 1). After sorting, the significance level changed to
P<.03 (Table 1). For the raw data, the significance level was
P<.06, and on the square root-transformed data, P<.05.
Graphing the raw data revealed that the greatest differences
between the SE and CE pigs was in rings 3 and 4 (Figures 13 and
14). Rings 1 and 2 (closer to the soma) showed less difference.
Pigs from the SE also had larger somas in the somatosensory
cortex than did those from the CE: 7.72 + 0.17 versus 7.27 +
0.17 (Table 1) (P<.08, raw data; P<.08 square root-transformed
data). Sorted soma widths did not differ significantly. Both
sorted and unsorted somatosensory cortex index scores differed
significantly between environments (Table 1) (P<.05 and P<.04,
respectively); the SE pigs had higher scores.
When the data were categorized according to trial, there
were no effects of rearing environment in Trial 1.
42
Environmental effects on TRI and index scores approached
significance in Trial 2 (Table 2) (P<.08 and P<.09); there was
a tendency for the SE pigs to have more dendritic branching.
When data from both trials for the visual cortex were
pooled, environment had no effect on TRI, soma size, or the
product index, (TRI x soma size) (Tables 3 and 4). Graphs of
the raw data for visual cortex in Trials 1 and 2 pooled
illustrate the lack of difference between treatments (Figures
15 and 16). When Trials 1 and 2 were analyzed separately there
were no treatment differences (Table 4).
There was a strong effect of gender on somatosensory
cortical traits when data from both trials were pooled. Gilts
had larger somas (7.78 + 0.17 versus 7.22 + 0.17, P<.03) (Table
5). However, there was no gender effect for visual cortex when
data from both trials were pooled (Table 6). Analysis employing
a gender X trial interaction model revealed an effect of trial
on TRI in both the somatosensory and visual regions of the
cerebral cortex (P<.03 for somatosensory unsorted; P<.006 for
visual sorted) (Tables 7 and 8); barrows had higher TRI in
Trial 1, gilts in Trial 2. Sorting changed significance levels
of the somatosensory TRI and soma size, but had little effect
on those for the visual cortex.
In Trial 1 there was a tendency for the CE pigs to touch
both the strange man and the novel object sooner. Mean times
to approach the strange man were: CE—59.5 ± 13 sec (mean +
SE), SE—100.3 ± 18 sec (NS). Approach times toward the
43
strange object were CE—49.8 + 13 sec and SE—83.5 ± 18 sec
(NS). Even though the mean times were not significantly
different, there was a significant difference between rearing
environments for the number of pigs which touched the man in
less than 60 sec. Nine out of 12 CE pigs touched the man in
less than 60 sec, whereas only 4 out of 12 SE pigs did go
(X2=4.19, P<.05). In the approach on object test, 9 out of 12
CE pigs touched within 60 sec, whereas only 5 out of 12 SE pigs
did go (X2=2.74, P<.10). When data for both the man and object
approach tests were combined, 18 out of 24 CE pigs touched
within 60 sec, whereas only 9 out of 24 SE pigs did go
(X2=6.85, P<.01).
In Trial 2, CE pigs were more willing to walk through the
chute. Mean times to walk through in the first test were:
CE—2.27 ± .53 min and SE—4.54 ± .37 min (P<.001). Mean times
for the second test were: CE—1.47 ± .53 min and SE—4.13
± .48 min (P<.001). Times were shorter for the second trial
compared to the first.
On the first chute test, 10 of 12 CE pigs walked through
within 5 min, whereas only 2 of 12 SE pigs did (X2=10.66,
P<.01). In the second test, 10 of 12 CE pigs walked through,
but only 4 of 12 SE pigs (X2=6.18, P<.02). When both tests
were combined, the results were: 20 of 24 CE pigs walked
through within 5 min, but only 6 of 24 SE pigs did go
(X2=16.540, PK.001).
44
Pigs in the SE engaged in significantly more nosing of each
other than pigs in the CE. The CE pigs had only 14 5-min periods
where nosing each other was observed whereas the SE pigs had 119
5-min intervals nosing each other (X2=194, P<.001). The CE pigs
also had greater overall rooting activity directed toward a
variety of objects (295 versus 215 5-min intervals, (X2 = 9.54,
P<.001).
The CE pigs directed over 90% of their rooting activity
toward objects, whereas the SE pigs spent up to 60% of their
rooting time, rooting each other.
Casual observations of the pigs during pen cleaning (SE
pigs) and petting (CE pigs) indicated that there may have been
a difference in the intensity of rooting and nosing. The CE
pigs nibbled gently on the straw, whereas the SE pigs rubbed
their noses intensely against the floor. Rubbing and massaging
another pig may be more stimulating to the somatosensory cortex
than rooting straw. The recipient of the massaging appeared to
react positively, often rolling over and presenting its belly
to the instigating pig. There also was a tendency for the SE
pigs that engaged in higher levels of nosing to have greater
dendritic growth.
The TRI scores for the three videotaped SE pigs were,
56.63, 45.05 and 50.90. The animal with the highest TRI score
also had the highest number of 5-min intervals which contained
rooting of the other pig. The number of 5-min intervals which
contained rooting were, 41, 37, and 38, respectively. The
45
animal that had the lowest TRI score had the highest number of
5-min intervals which contained rooting of objects in the pen.
Number of 5-min intervals which contained rooting of objects
was 15, 20, and 16, respectively.
The SE pigs were more excitable than CE pigs. They also
appeared to be actively seeking additional stimulation. During
pen washing, these pigs became highly excited and tried to bite
the hose and play in the water stream. Every time the
experimenter moved the water stream away from the pigs, they
jumped so as to be in it again. When the SE pigs were in an
excited state during pen cleaning, they often rubbed their
noses against the floor, perhaps in redirected behavior.
Furthermore, during feeder cleaning, the SE pigs would rush
forward and bite the experimenter's hand, and when they were
pushed away, they returned instantly and bit the hand again. In
the CE, the pigs were calmer and the experimenter could easily
push the pigs aside (and they stayed away for a while) while
cleaning the feeder.
Moreover, in the SE pigs, there were signs the animals
were active while people were absent. For example, unscrewed
bolts frequently were found on the floor.
0. Discussion
The experimental environments employed—simple (SE) and
complex (CE)—corresponded approximately to the SC and EC,
respectively, used in earlier rat and monkey experiments. Pigs
46
were not placed in an IC, for two reasons. First, Fleeter and
Greenough (1979) found no differences in cerebellar dendritic
branching between IC and SC monkeys. Second, isolation of
highly social animals such as monkeys and pigs may create
stress and abnormal behavior (Harlow and Zimmerman, 1959;
Melzack, 1954, 1969). In the interest of the pfgs' welfare, we
felt we did not have sufficient justification to subject the
animals to the stress of long-term isolation (IC).
Rats residing in the EC had greater dendritic branching in
the visual and temporal, but not the frontal, lateral cortex
(Greenough, 1984). Similar findings also have been found
in the neocortex of adult and middle-aged rats (Uylings et al.,
1978; Green et al., 1983; Volkmar and Greenough, 1972). Rats
residing in an enriched environment had a neocortex that was
heavier in several regions compared to those in standard 32 x
20 x 20-cm cages (Bennett et al., 1964; Diamond et al., 1964;
Katz and Davis, 1984). The enriched environment consisted of
groups of 10 to 12 rats residing in a large cage equipped with
ladders, platforms, exercise wheel, and other objects. For 30
min each day, the rats living in the EC also were placed in a
maze in which positions of barriers were changed daily (Bennett
et al., 1964). The control rats were housed in trios in small
(32 x 32 x 20-cm) cages.
Other brain studies revealed that rats from the EC also had
a thicker cortex (Bennett et al., 1964; Diamond et al., 1964).
Moreover, rats which had a thickened cortex also had additional
47
glia cells in the cortex (Diamond et al., 1966). The EC also
caused increases in a wide variety of interrelated brain measures
such as synaptic density (Turner and Greenough, 1985; Bhide and
Bedi, 1984) and ratio of oligodendrocytes to neurons in the
occipital cortex (Katz and Davis, 1984).
In the present experiment, the SE pigs had greater dendritic
branching in the somatosensory cortex than did the CE pigs. The
SE pigs also had pyramidal cells with larger somas. There was no
significant effect of environment on dendritic branching or soma
size in the visual cortex. These results are contrary to our
hypothesis that the CE pigs (corresponding approximately to EC
rats) would have increased dendritic growth. Results of previous
research on rats indicated that the EC enhanced dendritic
development in both neocortical and noncortical areas of the
brain (Fleeter and Greenough, 1979; Volkmar and Greenough, 1972;
Juraska et al., 1985).
The most likely explanation for the apparent anomalous
results in this experiment is direct stimulation of the
somatosensory cortex. Previous investigators have found that
exercise or sensory stimulation will augment neuroanatomy.
Exercise will increase dendritic branching in rat cerebellum
(Pysh and Weiss, 1979). Training a kitten to avoid a shock by
lifting its foreleg resulted in greater dendritic density in
the cortical area which receives sensory input from the forearm
(Spinelli et al., 1980). Tactile, vestibular, and other
sensory stimulation applied to young dogs increased the size of
48
vestibular neurons, while there were inconsistent differences
in frontal and auditory regions of the cerebral cortex (e.g.,
three of eight stimulated puppies had larger pyramidal cells)
(Fox, 1971). Shapiro and Vukovich (1970) also found that the
application of visual, auditory, and vestibular stimulation and
mild electric shocks to infant Sprague-Dawley rats increased
spine density in the visual and auditory regions of the
cerebral cortex.
Rubbing and massaging another pig may be more stimulating to
the somatosensory cortex than is rooting straw. Casual
observations indicated that SE pigs may have pressed harder with
their snouts than CE pigs. The recipient of the massaging
appeared to react positively, often rolling over and presenting
its belly to the instigating pig.
Placing an animal in a relatively barren environment will
increase excitability, irritability, and self-stimulatory
behavior. Pigs residing in a barren environment engage in more
activities involving the snout, van Putten (1980) found that
pigs housed on partially slatted floors without straw massaged
other pigs with their snouts twice as much compared to pigs with
access to straw. Stolba (1981) also reported that as the
environment was made increasingly barren, behaviors directed
toward other pigs increased. Less nibbling and massaging of
other pigs occurs in straw-bedded pens. Providing enrichment in
addition to straw further reduces activities directed toward
other pigs (Stolba, 1981).
49
From a sensory standpoint, the SE pigs may have been more
deprived than SC rats. The SE pigs had no bedding to root or
nibble. They were fed a diet in the form of a finely ground
meal, which required little time to consume. SC rats had
bedding material and hard food pellets to chew. In the
relatively barren SC condition, the rats still had access to
materials which enabled them to perform natural chewing
behaviors for long periods. Even though the rats could not
burrow in the bedding, they could still manipulate it. The
pigs had no substrate to manipulate. Small amounts of straw
will reduce stereotypies in tethered sows (Fraser, 1975).
Possibly, SE pigs engaged in greater amounts of abnormal
behavior than SC rats. This could have resulted in abnormally
high amounts of input to the somatosensory cortex.
Animals that engage in stereotypies often seek abnormally
intense amounts of stimulation. They even will sometimes
injure themselves in an effort to obtain stimulation (Cross and
Harlow, 1965). Among other things, stereotyped behavior
rewards the animal by releasing brain opioids. Self-
destructive behavior in retarded children and crib-biting in
horses are both stopped by administration of opioid blocking
drugs (e.g., Naloxone, Naltrexone) (Sandman et al., 1983;
Dodman et al., 1987).
Adrian (1943) reported that a major portion of the pig's
somatosensory cortex receives input from the snout, which is
one of the most sensitive parts of the pig's anatomy.
50
Therefore, when the SE pigs pressed their snouts against
something, presumably intense input was relayed to the
somatosensory cortex.
The greater intensity of activity of the SE pigs at pen
washing time and the observed intense activities involving
their snouts may explain the increased dendritic branching in
their somatosensory cortex. Pigs in barren pens with concrete
floors reacted more strongly and played longer with a tire than
did pigs reared in straw-bedded pens (Stolba and Wood-Gush,
1980). Pigs reared on concrete floors grazed and rooted with
greater intensity compared to pasture-reared pigs (Friend and
Taylor, 1986). The animals were observed on a pasture which
was novel to all animals.
The behavioral tests conducted at the end of the two
trials in the present study indicated that CE pigs behaved
differently than SE pigs. The SE pigs exhibited greater
avoidance responses when they were isolated in the novel arena
or chute apparatus. Ten of 12 SE pigs refused to walk through
the chute, whereas only two CE pigs refused. The SE pigs'
behavior was similar to that of unhandled rats. Rats that are
handled during infancy explore larger areas of an open field
(Levine et al., 1967). Melzack and Thompson (1956) found that
dogs reared in a restricted environment had greater avoidance
responses when a person approached.
The SE pigs sought stimulation, but it was an approach-
avoidance situation. The first few times the pens were washed,
51
the SE pigs panicked and fled to the rear of the pen. But when
they became habituated to pen washing, they approached and
excitedly bit at the water stream and hose. Within a few days,
pen washing had changed from an activity that triggered a
strong avoidance response to one that elicited strong approach
response. The SE pigs often defecated in the feeder. After
the experimenter cleaned it, they sometimes defecated in the
feeder again almost immediately. This suggests that they might
have been seeking stimulation from the presence of the
experimenter, however short the visit may have been. In a
totally novel situation, the SE pigs avoided novel stimulation;
but in their familiar pens, they actively sought stimulation by
belly nosing, biting the experimenter, and biting the water
stream and hose.
The SE pigs were more excitable than the CE pigs. Similar
observations have been made by other investigators in other
species. Animals in the IC were more excitable than were EC
animals (Korn and Moyer, 1968; Walsh and Cummins, 1975).
Isolation of mice increased reactivity, muscle tone, and
aggressive behavior (Valzelli, 1973). Pairs of puppies
confined to a barren cage with no visual contact with other
dogs responded to a new environment with increased activity
(Melzack, 1965). Puppy pairs became hyperexcitable even though
they could smell and hear other dogs. After being returned to
a normal environment a year later, the dogs still were more
excitable (Melzack, 1954). Walsh and Cummins (1975) found that
52
rats became hyperactive when their toys were changed.
Interestingly, the EC in the laboratory probably is relatively
simple compared to life outside the laboratory. A garbage dump
or a rural environment has greater complexity than a laboratory
cage filled with objects and otherwise enriched.
Quality of the environment affects behavior. Riittinen et
al. (1986) compared the effects of different environments on
behavior. Weanling mice were subjected to three different
environmental treatments: standard IC, IC with
overstimulation, and EC with objects. In the IC/overstimulated
condition, the mice were subjected involuntarily to intense
sound, light, and vibration. In the EC condition, they were
allowed to initiate and control their interaction with the
objects. Both IC and IC/overstimulated mice were more
irritable than the EC mice. Thus, both forced understimulation
and forced overstimulation increased irritability, as measured
while the mouse was being "attacked" by a bottle brush moving
toward it. The most frequent response to the bottle brush by
EC mice was escape, whereas IC and IC/overstimulated mice had a
higher frequency of beating their forepaws against the side of
the cage.
Increased dendritic branching or spine density does not
necessarily mean that the animal has been in a higher quality
environment. In monkeys, colony-reared animals had less
dendritic branching in the motor I and frontal regions of the
cerebral cortex compared to animals reared in an isolated
53
condition with ladders, objects, and swings (Stell and Riesen,
1987). Rats exposed to continuous lighting had greater spine
density in the visual cortex (Parnavelas et al., 1973), but
their retinas were damaged (Bennett et al., 1972; O'Steen,
1970). Stimulation of the hippocampus with an implanted
electrode induced axonal growth and reorganization of synapses,
but these new connections increased excitability and seizures
developed (Sutala et al., 1988).
In a developing nervous system, there is an overproduction
of neurons. As the brain matures, excess synapses are
eliminated. This seems to be a kind of biological sculpturing
process. Fifty to 70 percent of developing neurons are
eliminated in some parts of the developing embryonic nervous
system (Oppenheim, 1985). In Rhesus monkeys (Macaca mulatto)
excess synapses are still being eliminated before full
behavioral competence (Rakic et al., 1980). Rakic et al.
(1980) suggested that complete maturation may be related to the
elimination of synapses.
Maybe increased dendritic branching in the somotosensory
cortex of the SE pigs was caused by a decrease in synapse
elimination. Intense sensory input from the pig's snout may have
provided stimulation which prevented elimination of synapses.
During the course of the experiment, the pigs' brains were
undergoing rapid development. Brain weight increases rapidly
from birth to 20 to 22 weeks of age (Dickerson and Dobbing,
1966). Cholesterol levels also increase greatly during this
54
time (Dickerson and Dobbing, 1966). This is an indicator of
myelinization.
Different parts of the brain may respond differentially to
increased sensory input. In our experiment with pigs, and in
that of Stell and Riesen (1987) with monkeys, rearing
environment had no effect on the anatomy of the visual cortex,
but it affected other parts of the brain. In rats, EC-induced
changes in cortical depth were more variable in the
somatosensory cortex than in the visual cortex (Diamond et al.,
1964). Motor I cortex was augmented by increased physical
activity provided in an isolated EC condition (Stell and
Riesen, 1987). In the frontal cortex, there was a tendency for
the colony-reared monkeys to have the lowest levels of
dendritic branching compared to the IC and isolated EC monkeys.
In motor I cortex, monkeys in the two IC and the colony had
similar levels of dendritic branching (Stell and Riesen, 1987).
Increased dendritic growth in the somatosensory cortex of
SE pigs may have occurred in an abnormal manner due to extreme
sensory restriction relative to the snout. There is evidence
that direct stimulation from a sense organ is not the primary
mechanism of environmental enrichment effects on neural
hypertrophy. In cortical weight experiments, the greatest
changes occur in rat visual cortex. Cortical weight is greater
in EC animals kept in total darkness and in blind EC rats
(Krech et al., 1963; Rosenzweig and Bennett, 1969). Diamond et al.
55
(1972) stated that this indicates that vision is not the
primary cause of the EC effect in the visual cortex of rodents.
In the visual cortex of the rat, effects of environment
and gender interact in complicated ways. Within the visual
cortex, different cell populations respond differentially to
environmental enrichment in male rats as opposed to females
(Juraska, 1934). Apical oblique and basilar branches of layer
III pyramidal neurons had a smaller response to the EC in
females than in males. Layer V pyramidal neurons in both
genders showed equal amounts of dendritic growth.
Even within a single neuron, different types of synapses
react in different ways to environmental enrichment. Beaulier
and Colonnier (1987) found that an enriched environment caused
FS synapses to decrease, and each residual synapse widens.
Although RA synapse numbers do not change, the total contact
area in this case is 16% greater than in FS synapses. These
experiments provide support for the idea that an entire system
of the brain may respond differently to environmental
enrichment compared to another system.
Recent research by Black et al. (1987) revealed that the
paramedian lobule of the cerebellar cortex in rats trained in a
constantly changing complex acrobatic task had a thicker
molecular layer than rats subjected to large amounts of routine
exercise. Exercise on a treadmill or exercise wheel provided far
more physical activity than the acrobatic training (Greenough and
Bailey, 1988). Maybe some parts of the brain have increased
56
dendritic branching due to quantity of input whereas other areas
will respond only to increased quality of information-carrying
capacity of the input. Another possibility is that the animals
that performed the acrobatic task had to continually maintain
their balance while traversing narrow balance beams and teeter-
totters. The treadmill and exercise wheel would not force the
rats to actively maintain balance. Actively maintaining balance
on an unstable apparatus may have provided additional stimulation
to the cerebellum. Even though the balance center is located
outside the paramedian lobule, balance may affect it. In humans,
defects in both midline and lateral cerebellar zones will cause
gait difficulties (Oilman et al., 1981).
Depending upon the circumstances, there may be three
possible mechanisms which control neural responses to
environment: 1) neural hypertrophy increases in the EC due to
increased sensory input, 2) increased sensory input prevents
normal synapse elimination, or 3) more complex sensory input
due to active exploration and learning causes greater
development of dendrites and synapses.
The most likely explanation for these anomalous results is
that the SE pigs simply had greater nervous input to the
somatosensory cortex. Direct observations indicated that
rooting was more intense in SE pigs. Further research would be
necessary to verify these observations and permit conclusions
to be drawn.
57
The behavior of the IC pigs resembled the animals'
excitable behavior described in sensory restriction research by
Melzack (1954). Animals raised in an enriched environment were
less excitable than those in barren surroundings (Walsh and
Cummins, 1975). The excessive belly nosing exhibited by the IC
pigs may have been a futile attempt to reduce nervous system
arousal. Repetitive stereotypic behavior can serve a de-
arousal function (Dantzer and Mormede, 1983). The environment
that the IC pigs lived in was much more barren than would ever
be would ever be encountered in nature. In conclusion, the
extent of neuronal development in the pig's somatosensory
cortex cannot be used as a measure of environmental quality.
Another unexpected result was that the barrows had greater
dendritic branching in both the visual and the somatosensory
regions of the cerebral cortex in Trial 1 (Tables 8 and 9),
whereas in Trial 2 the gilts had more. Juraska (1984) found in
rats that gender had different effects in different cortical
layers. For example, there was little gender effect on visual
cortex in layer IV, but a definite effect in layer III. Within
the same gender, cortical layer has an effect on dendritic
branching in rats: "Granule cells with somata in the
superficial third of the granule cell layer had substantially
more dendritic material than those with somata in the deep
portions of the cell layer" (Green and Juraska, 1985).
Both apical and basilar processes were drawn for all
Trial 1 pigs, but the high frequency of apical process
58
transection rendered these structures useless for data
analysis. In Trial 2, no attempt was made to find cells with
relatively intact apical processes. This facilitated the
finding of more drawable cells close to the surface of the
cortex. Therefore, it is possible that in Trial 1 pigs many
cells were in deeper layers than was the case in Trial 2 pigs.
Further research would be required to verify differential
gender effects in different cortical layers of the pig.
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Figure 4. Location of tissue blocks in the somatosensory and
visual cortex of the pig.
68
LOCATION OF TISSUE BLOCKS
LOCATION OF REMOVED TISSUE
INDICATES SOMATOSENSORY CORTEX
SOMATOSENSORY CORTEX
LOCATION OF REMOVED TISSUE
INDICATES VISUAL CORTEX
VISUAL CORTEX
69
Figure 5. Location of sampled neurons in the somatosensory
cortex of the pig.
Step A. A line was drawn through center of white
matter and through gyrus on each side.
Step B. Line 1 is drawn through center of white
matter and through gyrus on each side.
Step C. Line 2 is drawn 90 degrees relative to
lines 1 on both sides.
Step 0. Line 3 is drawn 90 degrees relative to
line 2.
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between the center line and line 2. Sampling site B
is located on the center line.
70
71
Figure 6. Location of sampled neurons in the visual cortex of
the pig.
Step A. A line was drawn, centered on the sulcas.
Step B. Line 1s were drawn 90 degrees relative
to the center line. The point where
line 1 contacts the top of each gyri was
the sampling area.
72
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73
Figure 7. Layout of apparatus for testing pig behavior in Trial 1.
74
GATE
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LOCATION OF MAN OR NOVEL OBJECT
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Figure 9. Pig pyramidal neuron that complies with the sorting
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78
79
Figure 10. Pig pyramidal neuron that complies with the sorting
criteria.
80
81
Figure 11. Pig pyramidal neuron that has a basilar tree less
than 170 micrometers wide. This neuron does not
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82
83
Figure 12. Pig pyramidal neuron that has an asymmetrical basilar
tree. This neuron does not comply with the
sorting criteria.
84
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93
V. ENVIRONMENTAL ENRICHMENT REDUCES EXCITABILITY IN PIGS
A. Introduction
Rough handling, excitement, and excessive use of electric
prods on swine at the abattoir can have a detrimental effect on
pork quality (Calkins et al., 1980; Barton-Gade, 1985; Grandin,
1986). Some groups of pigs are more excitable and difficult to
handle than others, and these are more likely to be subjected
to excessive electric-prodding because they refuse to move
forward in an orderly manner and pile up more often.
Rearing environment can affect behaviors relevant to
handling. Pigs reared in indoor pens with minimal contact with
people were more excitable and difficult to load into a trailer
compared to pigs reared outside with frequent contact with people
(Warriss et al., 1983). Young pigs reared outdoors with access
to a variety of objects and daily contact with a human approached
both a novel object and a human stranger sooner than did those
reared in small barren pens indoors (Grandin et al., 1983).
In the research reported in this paper, we aimed in
Experiment I to determine the effect of substantial environmental
enrichment on excitability of pigs raised in small barren pens,
and in Experiment II to determine whether less environmental
enrichment would have a similar effect.
94
B. Experimental Procedure
Experiment I
Animals and housing. Sixty-four Landrace-si red crossbred
pigs weighing 8.7 kg + (SD=.42) on average at the start were
used in a 4-week trial. Four pigs were placed in each of
twelve 1.2 X 1.2-m, raised, solid-sided pens with expanded-
metal floors, under continuous illumination in a windowless,
mechanically ventilated room. The pigs ate from a self-feeder
and drank from a nipple.
Treatments. Two treatments—objects and mingling—were
arranged in 2 X 2 factorial fashion. Objects were used to
enrich some of the pigs' environments. Three 7-cm-wide 41-cm-
long white polyester-cotton strips were suspended to within 16
cm of the pen floor. They were spaced 30 cm apart across the
pen beginning 30 cm from either side and changed daily. A
person mingled with the pigs in some pens for 5 min daily. The
person opened the pen gate and petted all pigs that approached.
Gates on control pens were never opened.
Behavior rating. At the end of the trial, two independent
observers who were unfamiliar with and to both the pigs and the
experimental treatments rated the pigs in terms of
excitability. A rating scale of 1 to 4 was used, where 1 =
calm when person entered pen and 4 = active avoidance of
person. During the rating process, the observer opened the pen
gate and leaned over the pigs.
95
Experiment II
Animals and housing. One hundred twenty-eight Landrace-
sired crossbred pigs weighing 42.5 kg + (SD=2.26) and 43.5 kg +
(SD=2.60) on average at the start were used in Trials 1 and 2,
respectively. In Trial 3, one hundred eighty Hampshire-sired
crossbred pigs weighing 32.8 kg + (SD=2.43) on average at the
start were used.
The pigs were housed in a windowless, mechanically
ventilated building with fluorescent lighting. The lights were
on a timer which turned them on for 10 h during the daytime and
off for 14 h at night.
Four pigs were housed in each of 32 (Trials 1 and 2) or 46
(Trial 3) 1.35 x 2.25-m pens with partially slatted concrete
floors. The partitions between the pens were constructed from
steel bars. Pigs in one pen could observe the activities of the
pigs in adjacent pens.
Trials 1 and 2 lasted 60 days each. Trial 3 was 105 days
long. All animals ate from a self-feeder and drank from a nipple
waterer.
Treatments. Treatments were arranged in a 2 x 2 x 2
factorial fashion, with mingle drive and objects as factors in
Trials 1 and 2. In the control groups, a human never entered the
pens, but the pigs could observe people in the aisles, filling
feeders and mingling treatments in adjacent pens.
In the mingle treatment group, a person entered each pen and
assumed a squatting position. Pigs which approached the person
96
were petted gently. No attempt was made to pet pigs which failed
to approach. In Trials 1 and 2, mingling was conducted for 10
min per week during the last five weeks of the Trial. In Trial
3, mingling was conducted for 5 min per pen on weeks 8, 9, 10,
11, and 14.
For the driving treatment, a person entered each pen and
moved the animals into the aisle. The pigs were allowed to run
down one aisle and up another back to their pen for 1 min. The
approximate distance traveled was 45 m and they were handled
gently. The only force used was either light tapping with a
plastic stick or blocking with a solid panel. Driving was
conducted on the same weekly schedule as mingling.
In the object treatment group, people never entered the pens
unless objects were combined with another treatment. Three
pieces of black neoprene fiber-reinforced hose were suspended in
each pen from ropes attached to the ceiling. The hoses were 45
cm long with a 2.5-cm outside diameter. They were spaced 45
cm, apart and the ends of the hoses were 25 cm above the floor.
In Trials 1 and 2, the pigs had continuous access to hanging
rubber hoses for the duration of the Trials. In Trial 3, the
hoses were placed in the pen on week seven.
In the assertive mingle treatment (Trial 3 only) a person
entered each pen and assertively approached each pig and petted
it. The person petted every pig, even those that attempted to
move away.
97
Behavior rating. At the end of each trial, two
independent observers who were unfamiliar with and to the pigs
and the experimental treatments rated the pigs in terms of
excitability. The procedure was the same as in Experiment I,
except that in Experiment II the observer walked into each pen
to perform the ratings.
Statistical analysis. The experimental unit was a pen of
four pigs. Excitability ratings in Experiment I were analyzed
with a nonparametric two-factor analysis of variance (Zar,
1984). Excitability ratings in Experiment II's Trials 1 and 2
were analyzed with the a Kruskal-Wallace test.
A multiple comparison Tukey-type test using Dunn's
procedure was used in Trial 3 (Zar, 1984). This test was used
to determine the statistical differences between the
excitability ratings assigned to each treatment.
Weight gain data in all three trials were analyzed
usingthe SAS General Linear Models (analysis of variance)
procedure (SAS, 1982).
C. Results
Experiment I
Treatment had an effect on excitability (P<.03). Control
pigs were more excitable than pigs in any other treatment group
(Table 9). Pigs that had both cloth strips and mingling were
rated less excitable than those that had either cloth strips or
mingling alone.
98
Experiment H
Treatment had an effect on excitability (P<.003). In
Trials 1 and 2, control pigs were more excitable than pigs in
mingle, drive, objects, or combinations of these treatments
(Table 10). In Trial 3, control pigs were more excitable than
those pigs in the assertive mingle, objects and assertive
mingle, and objects and gentle mingle treatments (Table 11,
P<.05).
In Experiment II, there was no treatment effect on body
weight gain. The data are shown on Table 12 for Trials 1 and 2
and on Table 13 for Trial 3. Probability levels were P<.51 for
Trials 1 and 2 and P<.43 for Trial 3.
D. Discussion
In both Experiments I and II, environmental enrichment
procedures reduced excitability. In Experiment I, there was a
tendency for pigs which received both mingling and objects to
be even less excitable. In all trials of Experiment II, pigs
which received two or more environmental enrichment treatments
had a tendency to be less excitable than those which received
only one enrichment treatment. There also was a tendency in
both experiments for objects alone to reduce excitability.
The pigs in Trial 2 of Experiment II were a calm group of
animals, and the environmental enrichment treatments tended to
have less effect in that trial. At the end of the Trial 2, the
control pigs were calm and allowed people to touch them.
99
Conversely, in Trial 1 of Experiment II, the control animals
actively avoided a familiar experimenter when he entered a pen.
In Trial 3 of Experiment II, assertive mingle was more
effective than gentle mingle in reducing excitability. A
possible explanation is that all pigs were petted in the
assertive mingle groups, whereas in the gentle mingle groups
only those that approached the experimenter were petted. It
was surprising that only five minutes of mingling once a week
had such a considerable and consistent effect on excitability.
Placing animals in a restricted environment can make them
more excitable (Melzack, 1954; Walsh and Cummins, 1975; Korn
and Moyer, 1968). Isolation increased reactivity and muscle
tone in mice (Valzelli, 1973). Melzack and Burns (1965) found
that sensory-restricted dogs had highly excitable behavior and
abnormal electroencephalograms (EEG) for as long as 6 mo after
release from the restricted environment. A restricted
environment definitely increases brain excitability. Rats
housed singly in barren cages are more difficult to anesthetize
with sodium pentobarbital than those housed in group cages with
many objects with which to interact (Juraska et al., 1983).
The environmental enrichment procedures used in Experiment
II had no effect on body-weight gain. The absence of an
adverse effect on weight gain may possibly be explained by the
pig's perceptions of the person entering its pen. If an animal
perceives a person as a threat, weight gains may suffer. Pigs
intimidated by a person approaching and looming over them had
100
reduced weight gain (Gonyou et al., 1986). It was expected
that the assertive mingle treatment pigs in Trial 3 of
Experiment II would lower weight gain. The experimenter in may
have appeared to be less threatening than the experimenter in
Gonyou et al. (1986). In the experiment of Gonyou et al.
(1986), the experimenter walked through the pens but ignored
the pigs. In Trial 3 here, the experimenter approached each
pig and attempted to pet it. Pigs may perceive a person who
invades their flight zone, but does not react to them, as more
threatening than one who invades the animal's flight zone and
attempts positive interaction.
Even though the experimenter petted pigs which attempted
to escape, the animals were never struck or hit. Hemsworth et
al. (1981) also reported that when an experimenter shocked a
pig when it approached, weight gain decreased. The pigs
quickly learned to avoid being shocked by moving away, but they
probably still perceived the experimenter as a threat.
Previous experiments with farm animals indicate that they
can become accustomed to handling (Reid and Mills, 1962;
Thurley and McNatty, 1973; Hughes and Black, 1976; Hails, 1978;
Gross and Siege!, 1983). Cattle readily adapt to daily
weighing with no effect on weight gain (Peischel et al., 1980).
Hens accustomed to handling had no decrease in egg production,
but hens not accustomed to handling had lowered productivity
when handled (Hughes and Black, 1976). Chicks accustomed to
101
daily handling grew faster and had higher antibody titers than
unhandled chicks (Gross and Siege!, 1983).
In conclusion, simple environmental enrichment procedures
reduce excitability. Reducing excitability and providing
environmental enrichment would improve animal welfare and may
have the residual effect of reducing handling stresses during
transport and slaughter.
102
TABLE 9. Excitability ratings for pigs housed in enriched and nonenriched
environments (Experiment 1)
Environment
Nonenriched Enriched
Observer control Mingle Objects Both
1 3.67 2.67
2 4.00 1.33
Both 3.83 2.00
3.33
2.33
2.83
1.33
1.00
1.17
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TABLE 13. Weight gains of pigs reared under different, environmental
enrichment procedures in Experiment II, Trial 3
Environment
Enriched
Nonenriched Assertive Gentle
control Mingle (AM) Mingle (GM) Objects (0) AM + 0 GM + 0
72.0+0.90* 73.0+1.32 76.1+1.75 70.4+1.06 72.2+1.28 74.6+1.17
Mean _+ standard error of mean (kg). Each value represents 30 pigs.
107
VI. ENVIRONMENTAL EFFECTS ON EASE OF HANDLING OF PIGS
A. Introduction
When pigs balk and refuse to move, handlers are more likely
to become frustrated. This in turn may result in excessive
electric prodding and even abuse of the animals. Rough
handling and excessive electric-prod usage at the slaughter
plant can have a detrimental effect on pork quality and cause
petechial hemorrhages (Calkins et a!., 1980; Canadian Meat
Council, 1980; Grandin, 1984, 1986; Barton-Gade, 1985).
Rearing environment can affect behavior during handling.
Warriss et al. (1983) reported that pigs reared in indoor pens
with minimal contact with people were more difficult to load
onto a trailer. The main purpose of the study reported here
was to determine if small amounts of environmental enrichment
could affect the pig's ease of handling in a chute. A
secondary purpose was to develop a method for testing a pig's
reaction to handling.
B. Experimental Procedure
Animals and housing
A total of 128 Landrace-si red crossbred pigs weighing 42.5
kg (SD=1.61) and 43.5 kg (SD=1.84) on average at the start were
used in Trials 1 and 2, respectively. They were housed in a
windowless, mechanically ventilated building with fluorescent
108
lighting (175 lux). The lights were on a timer which turned
them on for 10 h daily during the daytime.
In each trial, four pigs were housed in each of 16 1.35 x
2.25-m pens with partially slotted concrete floors. To provide
additional control subjects against which to compare the
experimental treatments, an additional two pens of control
subjects were added in Trial 2. Partitions between pens were
constructed from steel bars so pigs in one pen could observe
the activities of those in adjacent pens. Pigs ate from self-
feeders and drank from nipples.
Treatments
Both trials lasted 60 d. Treatments were arranged in 2 3
factorial fashion, with mingle, drive, and objects as factors.
In the control groups, a human never entered the pens, but the
pigs could observe people in the aisles, filling feeders, and
mingling in nearby pens.
Mingling was conducted for 10 min once weekly during the
last 5 wk of the trial. In the mingle treatment groups, a
person climbed over the gate and actually entered each pen and
then assumed a squatting position near the center of the pen.
Pigs which approached the person were petted gently. No
attempt was made to pet pigs which did not approach.
Driving was conducted on the same weekly schedule as
mingling. For the drive treatment, a person opened the gate,
entered the pen, and drove the pigs into the aisle. The pigs
then were allowed to run down one aisle and up another, back to
109
their pen (the distance traveled was approximately 45 m, the
elapsed time <1 min). The pigs were handled gently at all
times. The only force used was either light tapping with a
plastic stick or blocking with a solid wooden panel.
In the objects treatment groups, people never entered the
pens unless the objects were combined with the mingle or the
drive treatment. The pigs had continuous access to the objects
for the entire trial. Three pieces of black neoprene fiber-
reinforced rubber hose were suspended in each pen from woven
cotton ropes attached to the ceiling. The hoses were 45 cm
long, had a 2.5-cm outside diameter, and were spaced 45 cm
apart, and their ends were 25 cm above the floor.
Test apparatus
A 4.8-m-long single-file chute was constructed from plywood.
The layout of the apparatus is shown in Figure 17. The inside
height and width dimensions were similar to chutes used in
commercial slaughter plants (43 cm wide X 70 cm high)
(Grandin, 1982). The sides and floor of the chute were natural
finish plywood. The top consisted of five 2.5-cm-OD galvanized
pipes running the length of the chute. The floor was covered
with expanded-steel mesh.
The crowd pen had 1.2 m-high plywood walls which were
painted white, and the floor was broom-finish concrete. There
were no bars over the top of the crowd pen. Each pig was
admitted to the crowd pen through a 0.9 m-wide steel door which
110
was painted brown and led directly from a main aisle of the
finishing house.
A single-animal swine scale (Marting Mfg. Co., Britt, IA)
painted bright orange was placed at the far end of the 4.8 m-
long chute. The tailgate of the scale was replaced by a
plywood vertical slide gate.
The entire apparatus was in a window!ess room illuminated
dimly to discourage the pigs from entering the chute. The
room and the entire apparatus were illuminated with two frosted
incandescent lamps. The brightest lamp (60 W) was placed over
the crowd pen, and a 15 W lamp was hung over the scale. Both
lamps were in aluminum reflectors suspended 1.5 m above the
floor. The lighting was designed to discourage the pig from
entering the chute. To further induce balking, a 30 cm-long
brass-plated chain (welded 1.27-cm links) was suspended in the
chute entrance, simulating the shocker chains that some
slaughter plants use to urge stubborn pigs to move.
Test procedure
Each pig was brought individually into the crowd pen, and
the door was closed immediately behind it. A timer was started
and the pig was allowed 2 min to voluntarily enter the chute.
If it failed to enter within 2 min, it was tapped and guided
with a semi-rigid 2.5 cm-OD plastic pipe. The handler reached
over the crowd pen wall to urge the pig. If this failed to
move the pig into the chute within 15 sec, the handler oriented
the pig's head toward the chute entrance and then gave it a
111
single 2-sec-long shock with a battery-operated prodder
(Hotshot Products, Savage, MN). If one shock failed to move
the pig into the chute, the handler gave the pig additional
shocks as needed to drive it into the chute. Pigs which walked
voluntarily through the chute and onto the scale within 1 min
were not prodded or touched. Pigs which backed up in the chute
were shocked once (as described) with the electric prodder, and
if they continued to back up they were again prodded (as
needed) to prevent further backing and make them move onto the
scale. The crowd pen, chute, and scale were kept wet at all
times. If a pig defecated or urinated in the apparatus, the
excreta was washed away before the next test. The person
handling the pigs was blind to the experimental treatment a
given pig had experienced. The same person handled all the
pigs in both trials. The following force ratings were given to
the urging necessary to accomplish moving a pig through the
chute.
Level I in crowd pen = moves into chute voluntarily within 2 min.
Level 2 in crowd pen = tapped and guided with plastic pipe.
Level 3 in crowd pen = shocked once.
Level 4 in crowd pen = multiple shocks.
Level 1 in chute = moves onto scale voluntarily within 1
min and without backing up (stopping
allowed).
Level 2 in chute = backed up and prodded once.
112
Level 3 in chute = multiple proddings required to prevent
pig from backing out and to drive it
onto the scale.
C. Results
In Trial 1, mingling reduced the force required to drive
pigs through the chute. Control treatment versus all treatment
combinations containing the mingle factor were significantly
different (X2 = 3.84, P<.05) (Tables 14 and 15). A higher
percentage of Trial 1 pigs in the control treatment and drive
treatment groups had to be prodded (Tables 14 and 15). Thirty-
eight percent of the control pigs and 40% of the drive
treatment pigs required level 3 or 4 force in either the crowd
pen or the chute. However, there was a tendency for all
treatments, including drive, to reduce the amount of prodding
performed. Twenty-five percent of the control pigs were
electric-prodded repeatedly (level 4 force), whereas no pig in
any of the treatment groups was (Table 16).
In Trial 2, the control pigs required the least force to
move through the chute (Tables 14 and 15). Comparison of control
pigs with those in all other treatment groups approached
significance (X2 = 3.62, P<.10).
Data for pigs which entered the chute voluntarily (force
level 1) are shown in Table 17. In Trial 1, fewer control animals
entered the chute voluntarily when compared to all other
treatments (X2 = 19.92, P<.001). There were no differences
113
between control pigs and those in the other treatment groups
for voluntary entry in Trial 2, although there was a tendency
for control pigs to enter more readily.
Treatment had no effect on dunging and urination in the
crowd pen. Treatment also had no significant effect on
vocalization during testing.
D. Discussion
Treatment effects varied greatly between Trials 1 and 2.
In Trial 1, mingling and objects reduced the force required to
move the pigs through the chute. Control pigs also were more
reluctant to enter voluntarily. In Trial 2, conversely, the
control pigs required the least amount of force to move through
the chute. Overall, the control pigs were the most difficult
to handle in Trial 1, but the easiest to handle in Trial 2.
Pigs studied in Trial 2 appeared to be tamer and calmer at
the start of the trial than those studied in Trial 1. This may
be explained by a change in farrowing house manager between the
two trials. The new manager was gentler, and the sows and
piglets under her care appeared to be calmer. Research by
Hemsworth et al. (1986) indicated that handled piglets are more
willing to approach a strange person later. The new manager
may have affected the pigs' behavior.
Ironically, very tame animals are often more difficult to
drive because they no longer have a flight zone (Grandin,
1987). They will no longer move away from an approaching
114
person. A change in personnel caring for the pigs and applying
the treatments during Trial 2 may have resulted in additional
taming. At the end of the trials, Trial 2 control pigs allowed
people to touch them, whereas Trial 1 control pigs quickly
moved away when approached. The new personnel were very
conscientious about good animal care and may have inadvertently
tamed the Trial 2 control pigs even further.
During Trial 2, time spent washing the pens was increased
from once to twice a week. The animals were often sprayed by
the hose and allowed to play in the water. Increased pen
washing may have tamed the controls. In Trial 2, the control
pigs received stimulation and contact with people which greatly
exceeded normal commercial practice. Casual observations also
indicated that the behavior of Trial 2 control pigs was similar
to pigs in certain treatment groups in Trial 1.
It is unfortunate that the two trials were conducted so
differently. But the results showed clearly that, within
respective trials, the rearing environment did affect the way
the pigs moved through the chute.
These results have implications for the handling of
livestock in farms, stockyards, and slaughter plants.
Observations under commercial conditions indicate that
excessively flighty or wild animals are more likely to pile up,
ram fences, and become injured than calm animals. A few wild
cattle mixed in with a group of tame animals will make the
whole group more excitable. A few excitable, balky pigs mixed
115
in with calm animals tend to spread excitement throughout the
group.
On the other hand, it is possible to get an animal so tame
that driving it becomes difficult. Cattle which have been
trained to lead with a halter are often difficult to drive.
These animals are accustomed to being led instead of being
driven.
There may be an optimal level of handling and contact with
people for a pig which will be fattened for slaughter. On the
other hand, sows and boars used for breeding probably would
benefit from greater amounts of handling. It is desirable to
have a calm animal that will be easy to drive, but not so tame
that driving is difficult. Excitable animals with excessively
large flight zones may be more likely to panic and become
injured or stressed, especially when confronted by a handler in
a confined area such as a slaughter plant stockyard.
Management procedures which improve the ease of handling at the
slaughter plant would greatly reduce costly bruises and stress-
induced meat quality problems.
116
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TABLE 15. Comparison of pigs that were electric-prodded any time
during the test
Environment
Trial Nonenriched control
Containing mingle
Containing objects
Containing drive '
1 3/8 prodded 2/32 prodded 3/32 prodded 7/32 prodded
38% 6% 10% 21%
2 2/15 prodded 9/32 prodded 8/31 prodded 9/31 prodded
13% 28% 26% 29%
No. of pigs prodded (force levels 3 and 4 combined)/total no. of pigs.
118
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VII. OBJECT INTERACTION IN WEANLING PIGS
A. Introduction
According to Fagen (1984), "play means behavioral
performance that emphasizes skills for interacting with the
physical and social environments and that occur under
circumstances under which the function of the exercised skills
can not possibly be achieved." Play in animals is difficult to
define. One way to narrow the definition is to determine which
activities are not play. Play is definitely not sleeping,
eating, elimination, mating, or serious fighting. In some
instances, play and exploration may be related. Due to the
difficulty of defining play, the word "play," will be put in
quotation marks.
"Play" occurs in many farm animals, including cattle, sheep,
pigs and horses (Brownlee, 1954, 1984; Tyler, 1972; Schoen et
al., 1976; Sachs and Harris, 1978; Van Putten, 1978; Dobao et
al., 1984-85), as well as a relative of the pig, the collared
peccary (Byers and Beckoff, 1981; Byers, 1984). It is
interesting that in these species both juveniles and adults
"play," because ordinarily in ungulates only juveniles and
subadult males "play" (Byers, 1984).
Object interaction, including "tug-of-war," has been
observed in dogs, cats, and jackals (van Lawick and Goodall,
1971; West, 1977; Fagen, 1981; Martin, 1984). Captive bushdogs
and foxes "play" with sticks (Biben, 1982). A captive
123
rhinoceros will root a ball and other objects (Inhelder, 1978;
Hediger, 1968). Piglets also engage in object "play"
(Gundlach, 1968; Fraedrich, 1974). Weanling pigs tugged on
cloth strips in a manner similar to that of dogs playing "tug-
of-war" (Grandin et al., 1983).
Farmers have offered pigs various objects in attempts to
enrich their environments and reduce vices. Van Putten (1969)
recommended placing chains or rubber hoses in pens to occupy the
pigs' attention and reduce tail-biting. Weanling pigs will
interact with many kinds of objects, and they vigorously
chewed, tugged, and shook suspended strips of cotton cloth
(Grandin et al., 1983). They rooted balls, boards, and plastic
boxesm and rolled them around. But when the objects became
soiled with excreta, the pigs lost interest in them. Suspended
strips of cloth seemed to hold the pigs' interest longer than
did suspended chains, clean objects more than soiled.
If pigs have preferences, it might be advantageous to give
them access to objects they prefer, to occupy their attention,
reduce vices, and improve health and productivity. In
Experiments I and II, we determined pigs' relative preferences
for different types of objects in short-term exposures. In
Experiments III and IV, we studied the time pigs spent
"playing" with suspended cloth strips (the objects preferred at
first) and characterized daily activity patterns of pigs with
access to objects. In Experiment V, we determined pigs'
relative preferences for different types .paof objects in long-
124
term exposures. In Experiment VI, the effect of suspended
cloth strips on fighting during mixing was determined.
B. Experimental Procedure
Experiment I—short term object preference: type
Eight Hampshire-sired crossbred pigs were used in each of
three 10-d trials. Two pigs were held in each of four vertical-
rod-sided 1.2 x 1.2-m pens under 24-h illumination (200 lux) in
a windowless room at 22 to 26 C. Pigs weighed 9.7 kg
(SD=0.98), 19.2 kg (SD=1.73), and 21.52 kg (SD=1.85) when
respective trials started. They had ad-libitum access to
pelleted starter diet in a self-feeder and a nipple waterer.
Two sets of three 41 cm-long objects were suspended in
each pen for 15 min some time between 1500 and 1800 h every
day. Objects in each set were: 1) a brass-plated chain
(welded 1.27-cm links), 2) a 5 cm-wide black 100% cotton cloth
strip with a 7-g nut tied to the bottom for ballast, and 3) a
black rubber hose (SAE J CRP, .64-cm ID). The objects were
suspended from a wooden bar which was 71 cm above the pen floor
and centered in the pen, parallel to the feeder. They were
fastened to 23 cm-long strings spaced 30 cm apart.
Each pig was observed for 5 min during each daily 15-min
period of access to objects. Orders of pig observation and of
objects on the bar were randomized daily. The observer stood
in the alley, in front of the feeder. Direct observations of
certain object-oriented behaviors were registered2<<2Datamyte
125
800, Electro General Corp. (now Datamyte Corp.), Minnetonka,
MN->> on d 3 through 10: 1) frequency of touching each object
(no./5 min, 2) duration of touching each object (min/5 min), 3)
frequency of biting each object (no./5 min), and 4) duration of
biting each object (min/5 min).
Experiment II—cloth object preference: texture
Methods in Experiment II were as in Experiment I except
that 16 Hampshire-sired crossbred pigs, weighing 10.7 kg
(SD=1.41) at the start of Trial 1 and 15.6 kg (SD=1.51) for
Trial 2, were studied, and the experimental play objects were 5
cm-wide white cloth strips made of three kinds of material: 1)
100% cotton bed sheeting, 2) 100% polyester satin, or 3) fake
fur (.95 cm-thick 100% acrylic pile).
Experiment III—daily object interactions
Eighty Landrace-si red crossbred pigs weighing 13.8 kg
(SD=1.26) and 11.5 kg (SD=1.52) when respective trials started
were used, 40 in each of two 28-d trials. Four pigs were
placed in each of 10 solid-sided 1.2 x 1.2-m pens under 24-h
illumination (200 lux) in a windowless room. They had ad-
libitum access to meal starter diet and a nipple waterer. Pigs
in five pens served as controls, while those in each of the
five experimental pens were provided three 7 cm-wide white
cotton-polyester strips suspended to 17.5 cm above the pen
floor from a wooden bar 71 cm above. The strips were changed
daily.
126
To record object-pulling activity on a 24-h basis, the
strips were tied by a knot to a 3-cm plastic chain link which in
turn.was attached to one end of a heavy string which passed
through a hole in the wooden bar. The string's other end was
attached to one leaf of a spring-loaded switch constructed from a
7.5-cm steel strap hinge. The other leaf of the hinge was
screwed to the top of the bar and an angle bracket with a light
spring attached held the stringed hinge leaf off a screw which
served as the electrical contact. When a pig pulled on a cloth
strip with sufficient force (130 g), it closed the switch by
pulling the hinge leaf against the screw. Each pull was
recorded by an event recorder3<<3Model 2755, Simpson Electric
Co., Chicago, IL.>>. Every object had its own channel. Thus,
the record reflected definite pulls but not certain other uses
of the objects, such as chewing and nosing.
Experiment IV—object interaction behavior
Forty-eight Landrace-si red pigs weighing 9.6 kg (SD=1.60),
8.6 kg (SD=2.88), and 7.7 kg (SO:1.44) when respective trials
started were used in two 7-d trials. In each trial, four pigs
were placed in each of six 1.2 x 1.2-m vertical-rod-sided pens
under 24-h illumination (200 lux) in a windowless room. Every
pen was equipped with suspended cloth objects as in
experimental pens in Experiment III.
Behavior of pigs in half the pens was
videorecorded4<<4Model NV8030, Panasonic Co., Secaucus,
NJ.>>'5<<5Model WV1150A, Panasonic Co., Secaucus, NJ.>> for one
127
24-h period (d 1 and 6) in each trial, with the camera mounted
directly over the pen. Fighting and play were quantified by
one-zero sampling every 5 min for each pen of mixed pigs
(Lehner, 1979). Head in the feeder and lying, respectively,
were determined by instantaneous sampling every five minutes
(Lehner, 1979).
Experiment V—long-term object preference
Twelve Hampshire-sired crossbred pigs were used in each of
two 13-d trials. The pigs weighed 8.9 kg (SD=0.70) and 11.0 kg
(SD=0.68) at the start of respective trials. Four pigs were
placed in each pen. Objects, pens, and environment were as in
Experiment I. Object-pulling activity was recorded as in
Experiment III. The pigs had continuous access to the objects.
The order of the objects on the bar was randomized daily
(three-dimensional contingency analysis).
Experiment VI—objects and fighting
One-hundred twenty-eight Hampshire-sired crossbred or
purebred Duroc pigs weighing 9.58 kg (SD=1.49) were used in
four trials. Eight pigs from four different litters were used
in each trial. The pigs were weaned and split into two groups
of four. Four pigs from each litter were placed in a pen where
they had continuous access to suspended cloth strips, and the
other four were placed in a pen with no objects. The cloth
strips and pens used during this 7-d period were the same as in
Experiment III. The strips were changed daily.
128
At the end of this 7-d period (on day 8), two pigs were
removed from each pen for regrouping (the remaining two were
regrouped the next day). On the first day of regrouping, four
pigs completely strange to one another were placed together in
each of four pens as described for Experiment IV. Half of
these pens were equipped with suspended cloth strips (as
described in Experiment III). Thus, there were four treatment
groups: objects before and after regrouping (OBJECTS/OBJECTS),
objects before but not after regrouping (OBJECTS/NONE), no
objects before but objects after regrouping (NONE/OBJECTS), and
no objects either before or after regrouping (NONE/NONE). The
remaining two pigs in each of the original pens were grouped on
day 9.
Each pen of regrouped pigs was observed for 24 h with
time-lapse video equipment (as described for Experiment III).
The video recorders were set at 1/18 normal speed. The data
collection method was the same as described for Experiment IV.
Each pen served as the experimental unit. Fighting and object
interaction data were analyzed with the SAS General Linear
Model (split plot analysis of variance) procedure (SAS, 1982;
Gill, 1986).
C. Results
Experiment I—short term object preference: type
Frequencies and durations of object touching and biting
are given in Table 18. Touching frequencies (mean ± SEM) in
129
Trial 1 were 6.6 ± .6 times/5 min for cloth objects vs. 4.6
± .3 for hose and 3.6 ± .3 for chain (Yates corrected chi-
square = 7.5, P<.05). In Trials 2 and 3, touching frequencies
were similar (CX2-7.29, P<.06).
Biting data indicated that cloth was the preferred object.
Pigs bit cloth objects 14.8 ± .5 times/5 min in Trial 1, 12.6
± .4 in Trial 2, and 13.7 ± .5 in Trial 3. Biting of the hose
was 3.0 + .5 in Trial 1, 9.1 ± .7 in Trial 2, and 6.1 ± .6 in
Trial 3. Chain was a distant third choice, with values of 5.4
± .3, 5.8 ± .5, and 5.6 ± .4, respectively. Chi-square values
for biting preference were 79.83 and 23.74, respectively
(P<.001). Duration of touching and of biting results for all
trials indicated that cloth objects were preferred whereas
chain was often ignored.
Experiment II—cloth object preference: texture
Frequencies and durations of touching and biting the objects
in Experiment II are given in Table 19. There were no significant
differences among objects for the pigs in general, although
individual pigs did have individual preferences. Three pigs
touched acrylic fur objects most often, two polyester, and one
cotton (Yates-corrected chi square = 5.06, P<.05), wheras 10
had no preference. Also, four pigs bit polyester strips most
often, two cotton, two acrylic, and two polyester or cotton
(Yates-corrected chi-square = 7.56, P<.01); six had no
preference. Again, group preferences were not evident, but
some individuals had distinct preferences.
130
Experiment III—daily object interactions
Object "play" tended to decrease over the period of 3
weeks. Mean object interaction time in wk 1 was 68.9 ± 12.0
min in Trial 1, and 60.4 ± 14.8 min in Trial 2. In wk 3, times
were 24.5 ± 4.2 min and 34.5 ± 4.7 min, respectively. There
was considerable variation among groups in time spent "playing"
with objects. During wk 1, interaction time varied from highs
of 143.4 (Trial 1) and 116.9 min (Trial 2) to lows of 35.4 and
10.1, respectively. During wk 3, interaction time varied from
highs of 40.58 (Trial 1) and 64.05 min (Trial 2) to lows of
4.56 and 19.18, respectively.
Object interactions followed a diurnal pattern, with the
two daily peaks coming around 0900 h and 1900 h, respectively.
These tended to be around an hour later in wk 3 than in wk 1
(Table 20).
Experiment IV—relationship of object interaction
and other behaviors
Frequency of object interactions had a tendency to
increase when the pigs were active. Figures 18, 19, 20, and 21
illustrate the number of pigs standing and eating of the 12
pigs in three respective pens. Both "play" and fighting tended
to occur at the same time. Figures 18 and 20 show the first
day of Trials 1 and 2, respectively, and Figures 19 and 21 show
the sixth day.
131
Experiment V—long-term object preference
Frequencies of object pulling are given on Figures 22, 23,
and 24. Object preference changed over the course of the 7-day
experiment. For both trials combined, the mean number of cloth
object pulls on day 1 was 4538 in 24 h. On day 7, mean cloth
pulls declined to 1072. Hose pulling for both trials combined
averaged 1601 pulls on day 1 and increased to 2450 pulls on day
7. Chain pulling averaged 1627 pulls on day 1 and declined to
only 380 pulls on day 7. Chain clearly was the least preferred
object.
During the 7-day period, the pig's preference switched
from cloth to hose. The difference between cloth and hose was
not statistically significant for any day, however the
regression of the difference was significant (P<.01). Figure
25illustrates the regression of the difference between cloth
and hose pulls. During the first 3 days, cloth pulling
decreased at a rate of approximately 717 pulls per day. On day
1 there were 2949 more cloth pulls relative to hose pulls, and
on day 7 there were 1378 more hose pulls relative to cloth
pulls (Figure 23).
Experiment VI—objects and fighting
The presence of objects in the pen during mixing of strange
pigs reduced fighting (Figures 26 and 27) (P<.02). The two
treatments, OBJECTS/OBJECTS and NONE/OBJECTS, had a mean of
23.34 (SD=8.58) and 23.25 (SD=7.96) of 5-min segments with
fighting. The two treatments, NONE/NONE and OBJECTS/NONE, had
132
increased fighting: 30.62 (SD=9.99) and 33.88 (SD=15.73),
respectively. The greatest amount of fighting occurred during
the first 4 h after regrouping (Figure 27).
The provision of objects for 7 to 8 d prior to mixing had
no effect on fighting (Figure 28) (P=.47). Pigs which had
access to objects prior to mixing had reduced "play" during
mixing (P<.10) (Figures 29 and 30). The data also were
adjusted to exclude 5-min segments which contained both
fighting and object interaction. Access to objects prior to
regrouping also had a tendency to reduce this "clean play"
(P<.10) (Figures 31 and 32).
D. Discussion
Pigs preferred cotton cloth objects as against rubber-hose
or chain in Experiment I. The pigs were smaller in Trial 1 than
in Trials 2 and 3 and seemed to have more difficulty mouthing the
hose, which often would swing away from a pig attempting to mouth
it. The larger pigs in Trials 2 and 3 were better able to grab
the hose, and this might partly explain why it was a close
second choice in Trial 2. The chain was least preferred by all
pigs in all trials. One interesting observation was that often
a dominant pig in a group would push another pig away from a
hanging object even though a duplicate object was available a
few centimeters away.
When long-term preferences were studied in Experiment V,
the pigs initially preferred cloth objects. At the end of the
133
two 7-day trials, preference switched from cloth to hose
objects. As the pigs' experience with the hose increased, they
became more adept at catching it in their mouths. The change
in object preference may be due to the pigs' learning how to
catch the hose in their mouths.
Pigs directed two basic behaviors toward cloth and hose
objects: 1) while holding the cloth or hose in the mouth, they
would bite it rhythmically (they did not tear the object, but
rather chewed it), and 2) they would perform a tug-shake, like
a dog playing "tug-of-war" with a towel (a pig would grasp
anobject by its teeth and then pull while shaking its head back
and forth). This tug-shake behavior was never observed being
performed with the chain. Perhaps the pigs preferred the cloth
because they could easily and comfortably perform both chewing
and tug-shake behaviors with it. The tug-shake may be the same
behavior a pig uses when it kills prey. Likewise, the badger
seems to imitate its killing shakes when it grasps an object
such as a rag and shakes it repeatedly with horizontal head
motions (Eibl-Eibesfeldt, 1978). Infrequently, a pig would nip
a cloth strip apart or pull a hose off its string.
Although duration of object interactions in Experiment III
declined as the trials progressed, pigs were still maintaining
active interest in the objects and devoting considerable time to
"playing" with them at the end of every trial. There was a
similar result in Experiment VI. The presence of objects for
one week prior to regrouping reduced "play" when objects were
134
introduced at time of regrouping (Figures 29, 30, 31, and 32).
Even though "play" behavior was reduced, the objects still
maintained the pigs' interest. In both Experiments III and VI,
approximately twice as much "play" occurred when the objects
were first introduced.
This suggests that they were being positively rewarded by
this activity. The initial prolonged activity may have been due
to the novelty of the objects, but in Experiment III "play" still
continued for almost 30 min per day after one week of exposure
to the objects. After seven days, the objects presumably were
no longer novel.
Another indicator of rewarding effects of "playing" with
objects was observed in Experiments I and II, in which the pigs
had access to objects for only 15 min daily. After five days
or so, the pigs anticipated the arrival of objects. When the
experimenter approached with the objects, the pigs invariably
would jump up repeatedly and try to touch them before they
could be secured to the overhead bar. The large finishing pigs
used in the excitability experiments reported in Chapter V
exhibited similar behavior; some animals that did not have toys
in their pens waited near the fence and caught a rubber hose
that swung near the fence.
Previous studies had shown that domestic livestock have
daily patterns for grazing and other activities (Hughes and Reid,
1951; Squires, 1974; Arnold and Dudzinski, 1978). Morrison et
al. (1968) found that pigs kept indoors were more active during
135
the daytime. Two peaks of activity—around 0900 and 1700 h,
respectively—have been observed in pigs, especially in
relatively rich environments (Dantzer and Mailha, 1972;
Dantzer, 1973; Bure, 1981). Curtis and Morris (1982) found
that pigs with operant control of environmental temperature
prefer warm afternoons and cool nights.
The daily patterns of "play" in Experiment III are in
agreement with the daily activity patterns charted by Morrison et
al. (1968).
The placement of cloth objects in the pen during
regrouping reduced the number of 5-min segments which contained
fighting. Changes in the rearing environment can reduce
fighting. McGlone and Curtis (1985) found that providing
small hides where pigs could place their head and shoulders
reduced fighting. A series of maze-like corridors in the
finishing house also reduced fighting (Nehring 1981).
Providing pigs with straw had a tendency to reduce fighting in
fasted pigs, but had no effect on fighting in pigs fed ad-
libitum (Kelley et al., 1980).
The objects may have served to distract the pigs from
fighting. In Experiment IV, both "play" and fighting occurred
during the periods when the pigs were most active. Even though
the presence of cloth objects prior to regrouping reduced
"play" behavior during the 24-h regrouping period (Figure 29),
it had no effect on fighting. The presence or absence of cloth
136
objects prior to regrouping had no effect on fighting during
regrouping of strange pigs (Figure 26).
There are several conclusions that can be drawn from this
series of experiments. When suspended objects are provided,
pigs have a definite preference for pliable objects. The hard
chain was the least preferred object. Some pigs had individual
differences in their preferences for cloth textures. "Play"
behavior occurs during the time of day when pigs are most
active and suspended objects maintained the pig's interest over
a period of 3 weeks. Suspended objects placed in the pen
during regrouping will reduce fighting in young newly mixed
pigs.
Experiments III and VI indicated that previous exposure
to objects reduced object interaction levels (Table 20; Figures
27 and 28). This may indicate that pigs in small barren pens
require additional stimulation. Perhaps pigs living in a more
stimulating environment would "play" less intensely with
objects placed in their enclosure. Weanling pigs reared in
small barren pens for 65 to 68 days (Chapter IV) appeared to be
seeking stimulation. When people were absent, they unscrewed
bolts. During feeder-cleaning, they rushed up and bit the
experimenter. They also excitedly bit at the water stream
during pen-washing. Pigs in small barren pens also engaged in
greater amounts of belly-nosing (Chapter IV). Van Putten
(1980) found that pigs on partially slatted floors without
137
access to straw belly-nosed more than did pigs with access to
straw.
Stimulus seeking also has been observed in rodents and
primates. Rats residing in a barren environment will bar press
more than rats in an enriched environment (Ehrlich, 1959).
Rhesus monkeys in an opaque cage worked hard at an operant
discrimination task. Successful completion of the task was
rewarded with a brief glimpse of the laboratory through an open
window (Butler, 1953). Simple practical objects such as cloth
strips or rubber hoses may be able to provide additional
stimulation and improve welfare in agricultural production
environments.
138
TABLE 18. Frequencies and durations of touching and biting of objects (Experiment 1)
Trial
1
Object
Cloth
Hose
Chain
Frequency (no./5 min)
6.6+,6*'
4.6+.3
3.6+.3
Touching
Duration (min/5 min)
.15+.02
.12+.01
.07+.01
Bitl
Frequency (no./5 min)
14.8+.5
3.O+.5
S.4+.3
ng
Duration (mln/5 min)
2.3+.09
0.2+.05
0.6+.06
2 Cloth
Hose
Chain
8.S+.6
9.0+.5
5.5+.4
.21+.01
.22+.02
.11+.01
12.6+.4
9.1+.7
5.8+.S
1.6+.08
0.7+.08
0.5+.05
3 Cloth
Hose
Chain
7.T+.6
6.0+.4
4.6+.S
.18+.02
.17+.02
.09+.01
13.7+.3
6.1+.6
5.6j ,4
2.0+.O9
.5+.07
.6+.06
Mean + standard error of mean.
139
TABLE 19. Frequencies and durations of touching and biting
of cloth objects (Experiment II)
Cloth object material
Cotton
Polyester
Acryl ic fur
Pooled SE
Frequency (no./5 min)
7.0
8.1
8.5
.61
Touching
Duration (min/5 min)
.18
.19
.24
.017
Bit ing
Frequency (no./5 min)
8 .3
9.5
8 .2
.59
Duration (min/5 min)
.92
1.21
.80
.097
140
TABLE 20. Midpoints3 of periods of greatest object pulling
(Experiment 111)
Touching Biting
Trial Wk I Wk 2 Wk 1 Wk 2
1 0730+36* 0954+24 1842+36 2048+42
2 0924+12 0924+18 1976+2.1 1754+24
Both 0827+24 0939+24 1909+28 1901+36
Mean + standard error of mean (time in h).
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VIII. SUMMARY OF RESULTS AND CONCLUSIONS
AND PROPOSED FUTURE RESEARCH
A. Summary of Results and Conclusions
Dendritic growth in somatosensory region of brain cortex in pigs
residing in a simple or a complex environment.
Rearing environment had a significant effect in dendritic
growth and soma size in the somatosensory cortex of young pigs.
It had no effect on these parameters in the visual cortex.
Pigs residing in pairs in small barren indoor pens (simple
environment, SE) had greater dendritic growth and larger somas
than 12 pigs living together in a large outdoor pen with straw,
play objects, and positive daily contact with a person (complex
environment, CE).
The pigs in the SE engaged in greater amounts of belly
nosing compared to the CE pigs. The CE pigs had greater
overall rooting activity toward a variety of objects, but 95%
of that activity was directed toward objects. Even though the
SE pigs had less overall rooting activity, only some 40% of
their rooting was directed at objects, and approximately 60% of
the time was spent rooting on the other pig. Casual
observations indicated that the SE pigs were more excitable and
aggressive toward the experimenter than the CE pigs.
172
Environmental enrichment reduces excitability jn pigs.
Experiment I
Environmental enrichment reduced excitability in young
weanling pigs which resided in small barren pens. Control pigs
were rated more excitable than pigs which had continuous access
to hanging cloth strips or 5 min of daily petting from a
person. Pigs which had two environmental enrichment treatments
were rated less excitable than pigs which had only one.
Experiment II
Smaller amounts of environmental enrichment also reduced
excitability in older finishing pigs. Controls were rated more
excitable than animals which received continuous access to
hanging rubber hoses, 5 min of weekly petting from a person, or
a weekly drive in the aisle. A combination of environmental
enrichment treatments was more effective than a single
treatment. Environmental enrichment treatments had no effect
on weight gain.
Environmental effects on ease of handling
In Trial 1, environmental enrichment treatments reduced the
force required to move finishing pigs through a single-file
chute. The treatments were continuous access to hanging rubber
hose objects (objects), gentle petting for 10 min weekly
(mingle), weekly drives in the aisle (drive) or a combination
173
of these treatments. In Trial 2, control pigs required the
least amount of force to drive them through the chute.
Trial 2 pigs were calmer and tamer at the start of the trial
compared to Trial 1 pigs. There may be an optimum level of
handling and contact which will produce a calm market animal that
is easy to drive, but not so tame that driving becomes difficult.
Trial 2 controls were calm and tame due to a change in farrowing
house manager between trials and increased pen washing in Trial
2. Pen washing is a form of handling, and in this case it
served to tame the controls. Trial 2 control pigs were further
tamed by the new farrowing house manager. Pigs in the mingle
treatment in Trial 2 became so tame that they refused to move
through the chute. Control pigs in Trial 1 were excessively
excitable, which made driving more difficult. In conclusion,
for animals that will be marketed for slaughter, it is
desirable to have a calm animal that is easy to drive, but not
so tame that driving is difficult.
Object interaction in weanling pigs
Experiment I
A short-term i5-min preference test indicated that weanling
pigs prefer suspended cloth strips. Chain was the least
preferred object. In three trials, duration of touching and
duration of biting indicated that pigs preferred cloth objects.
Duration of touching and biting of hanging rubber hoses was
174
reduced because the pigs had difficulty grabbing them with their
mouths.
Experiment II
A short-term 15-min preference test similar to Experiment I
indicated that pigs had individual preferences for different
cloth textures. In general, there were no group preferences but
there were distinct individual preferences.
Experiment III
Chewing and pulling suspended cloth objects decreased over a
period of 3 weeks from an average of approximately 1 hour to 20
to 30 minutes. Even though play decreased, the pigs still
actively played with the cloth strips at the end of the trial.
Experiment IV
Object interactions had a tendency to increase when the pigs
were most active. Play and fighting both occurred more often
when the pigs were standing or eating.
Experiment V
A 7-day preference test indicated that object preferences.
changed over the time. For the first three days of the
experiment, cloth objects were preferred. At the end of the 7-
day period, however, hanging rubber hoses were preferred.
Hanging chains were the least preferred objects all along. The
change from cloth to hose preference may be due to the
development of motor coordination. Observations showed that
175
small pigs often had difficulty grabbing the hose until they
had had some experience with it.
Experiment VI
The presence of hanging cloth strips during regrouping
reduced the number of 5-min periods which contained fighting.
The presence or absence of hanging cloth objects for seven days
prior to regrouping had no effect on fighting. Providing
hanging cloth strips for seven days prior to regrouping reduced
chewing and pulling of the strips during the 24-hour regrouping
period.
B. General Conclusions
Rearing environment has strong effects on both the central
nervous system and pig behavior. Small amounts of
environmental enrichment reduced excitability and fighting.
The provision of hanging cloth strips during regrouping of
young pigs reduced fighting. Suspended objects and small
amounts of contact with a person in the pen also reduced
excitability.
Environmental enrichment uniformly reduced excitability in
all the experiments, but it affected behavior during handling in
a complex manner. There may be an optimum level of contact with
people for animals which will be marketed for slaughter. Both
excessively excitable and overly tame animals are difficult to
drive and handle. In one trial, regrouping and objects reduced
the force required to drive pigs through a single-file chute.
176
But, in a second trial, the controls were easiest to drive. In
Trial 2, the pigs in the mingle group were overly tame and thus
difficult to drive. The recommended amount of environmental
enrichment for finishing pigs will vary depending on genetics
and the animals'previous experiences. Management procedures
which make pigs more amenable to handling at the slaughter
plant would help prevent costly bruises. They also would help
improve meat quality because excitement in the stunning chute
increases PSE and other meat quality problems (Barton-Gade,
1985; Grandin, 1986).
There has been increasing societal concern about the welfare
of farm animals residing in certain modern systems which provide
less varied sensory input than natural surroundings (Harrison,
1964; Singer, 1976; Mason and Singer, 1980; Fox, 1984. Some pigs
kept in barren pens on modern farms may be exhibiting symptoms
of sensory restriction. The animals are excitable, as may be
judged, for example, by their jumping up suddenly when a door
slams.
Excitability and increased irritability is a symptom of
sensory restriction. Pairs of puppies residing in barren kennels
become unusually aroused and excited when exposed to something
new (Melzack, 1954). Environmental restriction may have long-
term detrimental effects on the central nervous system. The
young dogs still had abnormal electroencephalographic patterns
6 months after being removed from the barren kennel (Melzack
and Burns, 1965). Animals living in an enriched environment
177
are usually less excitable than animals in barren surroundings
(Walsh and Cummins, 1975).
The experiments on dendritic branching and soma size in
young pigs indicate that rearing environment has significant
effects on nervous system development. The results were
contrary to the original hypothesis that animals in the
enriched environment (complex environment, CE) would have
greater dendritic branching. Volkmar and Greenough (1972)
found that rats residing in an enriched environment with
objects and other rats had more dendritic branching in the
visual cortex compared to pairs or isolates in plain cages.
Pigs reared in the simple environment (SE) had greater
dendritic branching in the somatosensory cortex. There were no
significant differences in dendritic growth in the visual cortex.
The behavior of the SE pigs differed significantly from
the CE pigs. The SE pigs engaged in greater amounts of belly-
nosing. Increased belly nosing may have stimulated the
somatosensory cortex. As the environment is made increasingly
barren, nibbling and massaging of other pigs will increase
(Stolba, 1981). The SE pigs also were more excitable and
aggressive toward the experimenter.
Rearing environment affects dendritic development in complex
ways. More dendritic development is not necessarily beneficial.
Monkeys reared in the colony had less dendritic branching in the
Motor 1 cortex compared to isolates in a cage with ladders and
swings (Stell and Riesen, 1987). Rats exposed to continuous
178
lighting had greater spine density in the visual cortex but their
retinas were damaged (Parnavelas et al., 1973; Bennett et al.,
1972; O'Steen, 1970).
Pigs in the SE condition appeared to be actively seeking
stimulation. Walsh and Cummins (1975) state that an organism
becomes increasingly sensitized to stimulation in an attempt to
restore balance. Lack of normal sensory input causes the areas
of the brain that receive sensory input to become more excitable.
Trimming the whiskers of baby rats causes the receptive field in
the brain to become more excitable and enlarged (Simons and Land,
1987). The receptive fields were still enlarged three months
after the whiskers had regrown.
Increased belly-nosing may have been an attempt to obtain
more stimulation and reduce arousal. The SE condition was more
barren than any environment which would exist in nature.
Perhaps the SE environment deprived the animals beyond their
ability to cope. The increased dendritic branching in the
somatosensory cortex of the SE pigs may be highly abnormal.
Experimental results indicate that simple and inexpensive
environmental enrichment procedures such as suspended cloth
strips or hoses and small amounts of increased positive contact
with people will reduce both excitability and fighting in young
pigs. Reducing excitability is advantageous for animal welfare
reasons. Excessive excitability may be a sign of detrimental
effects of sensory restriction in the nervous system.
179
C. Future Research
To elucidate the environmental factors which affect
dendritic growth in the somatosensory cortex, pigs should be
reared in barren pens with small amounts of environmental
enrichment such as "play" objects and extra contact with
people. The hypothesis would be that the small amounts of
environmental enrichment which reliably reduced excitability
would prevent belly-nosing and therefore prevent the abnormally
increased dendritic growth.
Further experiments also need to be conducted to accurately
quantify the differences between SE and CE pig behavior.
Observations indicated that both the quantity and the quality of
the rooting and nosing behavior was different between SE and CE
pigs. For example, SE pigs appeared to press harder during
rooting.
The effects of environmental enrichment on handling and
meat quality needs further study. Environmental factors affect
handling in a very complicated manner. Handling and care of
piglets in the farrowing house and nursery may have an effect on
driving and handling in chutes later.
180
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VITA
Temple Grandin was born August 29, 1947, at Boston,
Massachusetts. She grew up in the suburbs of Boston and took
her secondary education at Hampshire Country School, Rindge,
New Hampshire. As a girl, Temple was active in the 4-H horse
program for four years.
She attended Franklin Pierce College, also in Rindge,
where she majored in psychology and graduated as salutatorian
with a Bachelor of Arts degree in 1970. At Franklin Pierce,
she served as secretary of the Student Senate and was
recognized by her peers as the class member most likely to
succeed. She was listed in Who's Who Among Students in
American Colleges and Universities in 1970. She was active in
the FPC Psychology Club and handled publicity for the College
Social Committee.
In 1970, Dr. Grandin moved to Arizona to do graduate work
at Arizona State University, Tempe. She was awarded the Master
of Science degree in Animal Science in 1975. While a student
at ASU, she became livestock editor of Arizona Farmer-Ranchman
magazine. In this post, which she held for six years, Dr.
Grandin was an active supporter of 4-H and FFA beef, sheep, and
swine programs all over Arizona. She traveled extensively
around the state, covering livestock shows and sales and
writing feature articles for the magazine. In 1974, she also
worked for Corral Industries in Phoenix, Arizona, designing
feedlot equipment and coordinating advertising.
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Dr. Grandin became an independent livestock handling
consultant in 1975. She started practice in Arizona, and it
has since grown to cover 35 states, Canada, Mexico, Australia,
Denmark, Norway, England, New Zealand, People's Republic of
China, Saudi Arabia, and Sweden. She has clients in nine
Midwestern states. Dr. Grandin specializes in designing
livestock handling facilities for farms, feedlots, packing
plants, markets, and ranches. She has designed the following
facilities: ranch corrals, complete cattle feedlots,
stockyards, cattle hospital, cattle processing areas, sheep
corrals, chutes and crowd pens for handling cattle, pigs, and
sheep at the slaughter plant, dip vats, Kosher slaughter
systems, restrainer systems for humane slaughter, livestock
auctions, buffalo handling facility, wild horse feedlot and
handling facility, sheep ship loading system, loading ramps,
handling and sorting facility for university research feedlots,
large animal veterinary clinic, hydraulic and pneumatic
activated gates, and other projects. She also consults on
humane slaughter and electrical stunning methods and has worked
with many pork packing plants to improve handling and stunning
methods to reduce PSE and bloodsplash and advises on ways to
reduce bruises and injuries during handling and transportation
of all types of livestock.
The focus of her work is on improving the handling of
livestock and in reducing stress, bruising, and meat quality
problems. She has consulted with or designed equipment for
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dozens of firms and individuals, including Red River Feedyard
(then owned by the late John Wayne) in Arizona, Wilson Foods,
Washington State University, Glenn Kluck Feedyards in Nebraska,
Kahn's and Co. in Cincinnati, Illinois veterinarian Joe Connor,
Oscar Mayer in Iowa, Manitoba Hog Marketing Board in Canada,
Moyer Packing in Pennsylvania, John Morrell in North Dakota,
Spencer Foods in Iowa, Texas Tech University in Texas, Canada
Packer's in Canada, Danish Meat Research Institute, Australian
Government, U.S. Fish and Wildlife Service, and USDA Sheep
Experiment station in Idaho. Some of her most recent projects
include a new double rail restrainer system for slaughter
plants and a state-of-the-art stockyard at Hatfield Packing
Company in Pennsylvania.
In 1974, Dr. Grandin joined the Livestock Conservation
Institute and became a member of LCI's Livestock Handling and
Safety Committee. She became chair of the committee in 1976,
and has developed several educational materials on livestock
handling and transportation for LCI. These publications have
been distributed to producers, universities, and packing plants
all over the United States and in many other countries. In
1986, she became a contributing editor to Meat and Poultry
Magazine.
In 1982, Dr. Grandin became a graduate student in the
University of Illinois Department of Animal Science; she earned
her doctoral degree in 1988. She conducted research on pig
behavior under the tutelage of Dr. Stanley Curtis. She
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maintains an active consulting practice—as Grandin Livestock
Handling Systems, Inc., Urbana, Illinois—and is in heavy
demand as a speaker at meetings of producers, packers, and
scientists all over the world.
She has 10 refereed scientific papers, 7 refereed
extension publications, 22 abstracts and papers at the American
Society of Animal Science and American Society of Agricultural
Engineers, 27 educational publications, 47 meeting proceedings
papers and reports, and 113 livestock trade publications.
Dr. Grandin participates energetically in several
professional societies, and was a director of the American
Society of Agricultural Consultants. Other memberships include
the American Society of Animal Science and its Midwestern
Section, American Registry of Certified Animal Scientists,
American Meat Science Association, Council for Agricultural
Science and Technology, and American Association for the
Advancement of Science. She is an associate member of the
American Society of Agricultural Engineers.
The Wisconsin Veal Growers Association gave Dr. Grandin
special recognition in 1982 for her work related to the welfare
of veal calves. Livestock Conservation Institute presented her
the Meritorious Service Award in 1984 and she was nominated for
Midwest American Society of Animal Science, Outstanding Young
Extension Industry Specialist Award in 1984.
Dr. Grandin has lectured on livestock handling, facility
design and human slaughter methods in six different animal
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science and veterinary courses at the University of Illinois.
She has lectured on livestock handling throughout the United
States, Canada, Australia, and Europe.
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PUBLICATIONS
Publications
Grandin, T. 1979. Designing meat packing plant handling facilities for cattle and hogs. Transactions of American Society of Agricultural Engineers 22:912-917.
Grandin, T. 1980. Observations of cattle behavior applied to the design of cattle handling facilities. Applied Animal Ethology 6:19-3.1.
Grandin, T. 1982. Pig behavior studies applied to slaughter plant design. Applied Animal Ethology 9:141-151.
Blackmore, O.K., J.C Newhook, and T. Grandin. 1983 Time of onset of insensibility in four to six week old calves during slaughter. Meat Science 9:145-149.
Grandin, T. 1984/1985. Race system for cattle slaughter plants with 1.5 m radius curves. Applied Animal Ethology 13:295.
Grandin, T., S.E. Curtis, T.M. Widowski, and J.C Thurmon. 1986. Electro-immobilization versus mechanical restraint in an avoid- avoid choice test for ewes. J. Anim. Sci. 62:1469-1480.
Grandin, T. 1986. Minimizing stress in pig handling. Lab Animal 15:15-20.
Grandin, T., O.0. DeMotte, W.T. Greenough, and S.E. Curtis. 1988. Perfusion method for preparing pig brain cortex for Golgi-Cox impregnation. Stain Technology 63:177-181.
Grandin, T. 1988. Double rail restrainer conveyor for livestock handling. Journal Agricultural Engineering Research 41 (In press).
Ray, T.C., L.J. King, and T. Grandin. 1988. The effectiveness of self-initiated vestibular stimulation in producing speech sounds in an autistic child. Journal of Occupational Therapy Research 8:186-190.
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Extension Materials
Grandin, T. 1983. Design of cattle handling corals and squeeze chutes. Fact Sheet, Range Beef Cow Management Handbook, Great Plains Extension-9 (GPE-9).
Grandin, T. 1983. Livestock psychology and handling facility design. Fact Sheet, Range Beef Cow Management Handbook, Great Plains Extension-9 (GPE-9).
Grandin, T. 1983. Handling newly arrived feeder cattle. Fact Sheet, Beef Cattle Feeding Handbook, Great Plains Extension-9 (GPE-9).
Grandin, T. 1983. Reducing transportation stress. Fact Sheet, Beef Cattle Feeding Handbook, Great Plains Extensions-9 (GPE-9).
Grandin, T., J.J. McGlone, and K. Ernst. 1989. Hog handling. National Pork Industry Handbook (In press).
Grandin, T. 1989. Sheep behavior and handling principles. Sheep Industry Development Handbook (In press).
Grandin, T. 1989. Corral systems for sheep. Sheep Industry Development Handbook (In press).
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such as mingling and objects (hanging rubber hoses) were
more effective than a single treatment. Environmental effects
on handling behavior were complex. In one trial, mingling and
objects reduced the amount of prodding required to move pigs
through a chute. In another trial, mingled pigs were more
difficult to drive. There may be an optimal level of tameness
for pigs which will be marketed for slaughter. In barren pens,
hanging cloth strips (objects) reduced fighting in newly mixed
pigs. One week of exposure to objects prior to mixing reduced
biting and pulling of the objects during mixing. Previous
exposure to objects prior to mixing had no effect on fighting.
When objects were first introduced, activity was intense, and
it leveled off at a lower level. The pigs appear to seek
stimulation. Simple enrichment procedures may alleviate the
effects of sensory restriction.