AN ABSTRACT OF THE THESIS OF
John M. Marcek
in Animal Science
for the degree of Master of Science
presented on September 26, 1983
Title: THE EFFECT OF PHOTOPERIOD ON MILK PRODUCTION AND
PROLACTIN IN HOLSTEIN DAIRY COWS
Abstract approved:Redacted for Privacy
Lloyd V. Swanson
Fourteen multiparous Holstein cows were paired by stage of
lactation and previous years milk yield and 14 Holstein first-calf
heifers were paired by stage of lactation. One member of each pair
was assigned to a 24L:OD or a 18L:6D photoperiod for 16 wk during
winter 1981 (Experiment 1). A similar experiment comparing natural
photoperiod (9-12 h light/day) and 18L:6D was conducted for 9 wk
during winter 1982 (Experiment 2) in which 24 Holstein cows and 22
Holstein first-calf heifers were paired and assigned to groups as
in the first experiment. Animals were housed in a free stall barn
open on 2 sides. High pressure sodium vapor lamps provided light
intensity at cow eye level of 254 26 lux during the day and 132 9 lux
at night. In Experiment 1, concentration of serum prolactin (PRL)
in response to thyrotropin releasing hormone (TRH)(33 ig/100 kg BW)
was measured in 5 animals from each group. Prolactin response to
TRH or saline was tested in 10 animals in each group in Experiment 2.
Photoperiod had no effect on 4% fat corrected milk (FCM) in either
age group in Experiment 1 although cows in the 18L:6D group averaged
2% higher monthly persistency in 4% FCM over the 12 wk that milk
composition was monitered. Cows in the 18L:6D group averaged 5%
higher monthly persistency in 4% FCM in Experiment 2 as compared to
cows exposed to a natural photoperiod. Persistency in heifers was
unaffected by photoperiod in this experiment. Basal concentration of
serum PRL was not affected by either age or photoperiod in Experiment
1 (21.3±3.3 ng/ml). Peak concentration of serum PRL after TRH
injection was not affected by photoperiod in the heifer group but
cows exposed to 18L:6D had significantly higher concentrations of
serum PRL after TRH injection than cows exposed to 24L:OD (560±133
vs. 229±54 ng/ml). Basal concentration of serum PRL in Experiment 2
was similar in TRH- and saline-injected animals (26.3±3.1 ng/ml)
but was lower in cows than in heifers (17.1±2.0 vs. 35.5±5.0 ng/ml).
Saline injection did not elicit a PRL increase nor were there any
differences in concentration of serum PRL due to either photoperiod
or age after TRH stimulation in Experiment 2. Weight gain of cows
did not differ due to photoperiod in Experiment 1 although heifers
exposed to 24L:OD gained more weight than those exposed to 18L:6D.
Cows in Experiment 2 gained significantly more weight when exposed
to 18L:6D. No difference in weight gain due to photoperiod was
observed for heifers in Experiment 2. We conclude that milk yield
in mature cows can be increased by using supplemental lighting during
winter months when compared to natural photoperiod. No differences
between 18L:6D and 24L:OD were observed. Prolactin does not appear
to be involved in the mechanism of action of photoperiods stimulation
of milk yield. Cost analysis of the above data reveal a $16.06 return
on each dollar invested for supplemental lighting. The additional
income realized through supplemental lighting may allow the
dairyman to reduce herd size and operating costs.
The Effect Of Photoperiod On Milk ProductionAnd Prolactin In Holstein Dairy Cows
by
John M. Marcek
A THESIS
submitted to
Oregon State University
in partial fulfillment ofthe requirements for the
degree ofMaster of Science
Completed September 26, 1983
Commencement June 1984
APPROVED:
Redacted for PrivacyProfessor offAnimal Science in charge of major
Redacted for Privacy
Head of Department of Animal Science
Redacted for Privacy
Dean of Gradi4te School
Date thesis is presented September 26, 1983
Typed by Lisa M. Harris for John M. Marcek
ACIZiOWLEDGEHENT
I would like to thank Dr. Lloyd V. Swanson, my advisor and close
friend for his inspirations and insights throughout the course of my
work. From the intricacies of the laboratory to the unclimbable peak
of Mt. Washington he provided encouragement and enthusiasm to help me
complete my tasks. I would also like to thank the Oregon Agricultural
Experiment Station and the Oregon Dairymans Association who provided
the funds necessary for me to pursue my studies. Special thanks are
also extended to Dr. Fredrick Stormshak whose support, humor, and love
of science served as an inspiration to me. My fellow graduate students
also deserve many thanks for their neverending support, understanding,
and encouragement.
I would also like to express my appreciation to both my parents
and my in-laws for their continued love and encouragement during the
past two years. My dog Harry, who always had time to listen, also
deserves special mention.
Finally, I wish to express my deepest appreciation to my wife
Tricia, whose continued love and support helped me get through the
hard times, and made the good times more enjoyable.
TABLE OF CONTENTS
Chapter 1 Introduction 1
Chapter 2 Review of Literature 4
Chapter 3 Effect of Photoperiod on Milk Production andProlactin in Holstein Dairy Cows 19Abstract 20Introduction 22Materials and Methods 24Results and Discussion 27References 47
Chapter 4 Conclusion 49
Bibliography 52
Appendix 59
LIST OF FIGURES
Figure Page
1 Mean weekly milk yields for heifers in Experiment 1exposed to two photoperiods (18L:6L and 24L:OD) . . . . 37
2 Mean weekly four percent fat corrected milk (4% FCM)for heifers in Experiment 2 exposed to two photoperiods(18L:6D and natural) 39
3 Mean weekly milk yield for cows in Experiment 1 exposedto two photoperiods (18L:6D and 24L:OD) 41
4 Mean weekly four percent fat corrected milk (4% FCM)for cows in Experiment 2 exposed to two photoperiods(18L:6D and natural) 43
5 Mean weekly kilograms milkfat per day for cows inExperiment 2 exposed to two photoperiods (18L:6D andnatural) 45
Appendix Figure 1Mean weekly kilograms feed consumed (as fed) per day forcows exposed to two photoperiods (18L:6D and 24L:OD) . . 65
Appendix Figure 2Mean weekly kilograms feed consumed (as fed) per day forheifers exposed to two photoperiods (18L:6D andnatural) 67
Table
1 Serum prolactinheifers at restleasing hormoneExperiment 1
2 Serum prolactinheifers at restleasing hormoneExperiment 2
LIST OF TABLES
concentration (ng/ml) in cows and(basal) and after thyrotropin re-(TRH) challenge (33Pg/100kg BW)
concentration (ng/m1) in cows and(basal) and after thyrotropin re-(TRH) challenge (33pg/100kg BW)
3 Mean monthly body weight (kg) of cows and heifersexposed to various photoperiods
Appendix Table 1Mean weekly kilograms feed consumed (as fed) per dayfor cows and heifers in Experiments 1 and 2
Appendix Table 2Accuracy of KaMar Heatmount Detectors in cows andheifers in Experiment 1
Page
34
35
36
62
63
The Effect of Photoperiod on Milk Productionand Prolactin in Holstein Dairy Cows
INTRODUCTION
Photoperiod or length of daily exposure to light, natural or
artificial, has recently been studied as one of the important
biological cues by which physiological changes are controlled in
animals. Animals in the wild respond to changes in photoperiod in
several ways. Hibernation and migration are examples of these
responses although photoperiod is not the only environmental cue
involved in these phenomena. The greatest potential application
of these physiological changes for man's benefit is in farm animals.
The use of gradually changing photoperiod, constant long or short
photoperiod, and intermittent photoperiod have long been known to
poultrymen. By manipulating photoperiod, growth, maturation rate,
and other traits can be enhanced to increase production in chickens.
Intermittent lighting provides a double savings by stimulating
physiologic changes in chickens as well as decreasing the usage
of electricity.
Photoperiod is also an important environmental cue in the
regulation of sexual activity in seasonal breeding animals. There
are two types of seasonal breeders, those that breed as daylength
decreases (short day breeders, such as sheep) and those that breed
as daylength increases (long day breeders, such as the horse). The
seasonality of breeding is important for survival of the young.
Sheep, which normally breed in autumn when photoperiod is decreasing,
will lamb in spring when temperatures are warmer and grass is
2
becoming more abundant for the growing lambs. Horses have a much
longer gestation period. They breed in spring as daylength is
increasing and will foal the following spring when pasture is lush
and abundant. Horses also provide an example of manipulation
of breeding season through the use of artificial photoperiod. Most
horse registry associations consider January 1 to be the beginning
of a new registration year, making it advantageous to the breeder
to have his horses foal as close to (but after) January 1 as possible.
To do this the normal breeding season must be advanced from April
or May to February or March. Enclosed photoperiod-controlled barns
have made this possible.
The effects of photoperiod on reproduction are many. This
thesis deals only with production traits of farm animals. Recent
experiments in sheep have shown that by manipulating photoperiod,
growth rate may be increased, possibly decreasing the length of
time necessary to produce market lambs. Cattle also respond to
increased photoperiod with increased growth rates. Reports of
photoperiods effects on growth rate in swine are not yet conclusive.
In the past five years, evidence has been presented which
indicates that supplemental lighting will stimulate lactation in
the dairy cow. Increased length of photoperiod is a factor easily
controlled in our modern dairies. The objective of this thesis is
to investigate the effects of supplemental lighting on milk pro-
duction in dairy cows during winter when natural photoperiod is
short. The economic gains which may be realized by the dairyman
through the manipulation of photoperiod are great, especially in
3
the large freestall barns typical of Oregon. Most cows in these
barns are subjected to little or no supplemental light during
winter months when daily photoperiods range from 9 to 12 hours of
light per day. Although night lights are generally used, they
may provide insufficient intensity to be stimulatory to milk
production. In addition, the possible involvement of prolactin
(PRL), a hormone which is known to be influenced by photoperiod
and is essential for lactation in the bovine, will be investigated.
4
REVIEW OF THE LITERATURE
Chickens
The influence of photoperiod on growth and egg production in
chickens has been known for many years. Photoperiod influences
growth rate in chickens by changing feed intake patterns. Siegel et
al. (1963) observed that chicks exposed to 6 hours of light: 18
hours of darkness per day (6L:18D) grew faster than those exposed
to 14L:10D photoperiods. Feed intake data showed that chicks
exposed to shorter photoperiod learned to eat during the dark
portion of the cycle, whereas those exposed to a longer photoperiod
fasted most of the night (Morris, 1967a). Total feed intake over
the 24 hour period did not differ between the two groups. In
contrast, Squibb and Collier (1979) have observed that feed intake
occurs uniformly when chicks are exposed to continuous light. The
constant flow of nutrients to the tissues can then be used more
efficiently in the growing bird. Early experimenters observed that
chicks can be reared in constant darkness without any reduction in
body weight (Cherry and Bardwick, 1962; King, 1962). Later research,
however, indicates that continuous light has a distinct advantage
over light-dark sequences or constant darkness (Van Tienhoven and
Ostrander, 1976).
Intermittent lighting has been used by commercial broiler
producers mostly as an energy saving mechanism. Barott and Pringle
(1951) observed a stimulatory effect of intermittent lighting when
compared to 12L:12D; however continuous light still maintained the
5
highest weight gains (Beane et al., 1962). Generally, any system
of lighting that does not impose periods of rest, which decreases
feed intake, will increase growth rate. This is done most easily
with continuous light or continuous dark (Morris, 1967a).
Light intensity is an important factor regulating growth rate.
Cherry and Bardwick (1962) and Skoglund and Palmer (1962) reported
decreased weight gains associated with higher intensity lighting.
Intensities in these experiments ranged from 0.4 to 1200 lux. In a
commercial flock where lighting sufficient for feeding, maintaining
equipment and observation of birds must be maintained, management
is the key factor to determine the lower limit of light intensity
to be used. Cherry and Bardwick (1962) observed no difference in
growth rate attributable to red or white light at two intensities.
Green light (545 nm) also was effective as a growth stimulant
(Menaker, 1971).
Altered photoperiod also can stimulate or retard age at sexual
maturity. Data from several experiments suggests that chicks respond
to varying lengths of photoperiod in a curvilinear fashion with the
earliest sexual maturation occurring in chicks exposed to 10 hours
of light per day (Morris, 1967a). The influence of photoperiod on
sexual maturation is most evident when a changing photoperiod is
used. Chicks reared on increasing or decreasing photoperiods will
respond with an increased or decreased rate of maturation, respectively
(Morris, 1979; Tucker and Ringer, 1982). The important factor in
this instance is not the length of day but the rate of change
(Morris and Fox, 1958). Chicks hatched in winter and early spring will
6
mature precociously if exposed to the slowly increasing natural
photoperiods seen in higher latitudes during this time of year.
Although it may appear advantageous for birds to begin laying at
a younger age, smaller eggs, higher incidence of uterine prolapse,
increased mortality, and overall decreased egg production have been
reported (Morris and Fox, 1958; Morris 1967a, 1979). Delaying
maturation by supplying extra light or decreasing daily photoperiod
will increase the weight of eggs subsequently laid (Morris and
Fox, 1958; Tucker and Ringer, 1982), as well as increase the number
of eggs laid in the first year of production (Morris and Fox, 1959).
By manipulating photoperiod, age at maturity and subsequent maximum
egg yield can be obtained. Best yields have been obtained by
choosing a photoperiod designed to maximize ovulation rate (Morris,
1979). Gradually increasing the photoperiod as chicks approach
maturity (i.e. 18-20 weeks of age) results in increased egg production.
Increasing the photoperiod at this age has more profound effects
than if increased at an earlier age because the birds are more
sensitive to photoperiod changes as they approach maturity (Morris,
1967a). The intensity of light does not seem to be a major factor
in determining age at initiation of egg laying as pullets have
been reared successfully in both high and low intensity light
(Morris, 1967b).
Egg production is maximized by exposing birds to increasing
photoperiods to a maximum of 16 hours of light per day; further
increases do not result in increased egg production (Morris, 1967a;
Tucker and Ringer, 1982). Pullets therefore must be raised on short
7
photoperiods so that increases in daily photoperiod may be
implemented. Constant photoperiods of 6 to 10 hours of light per
day stimulate egg production compared to shorter photoperiods
(Morris, 1979).
Intermittent lighting is a topic of interest to many producers.
Experiments by Van Tienhoven and Ostrander (1976) have shown that
birds exposed to 2L:10D:2L:10D or 2L:12D:2L:8D maintain equal egg
production, egg weight, and feed efficiency when compared to birds
exposed to 14L:lOD. The savings of 10 hours of electricity per
day without reduction in production would have significant impact
on the poultry industry. A minimum intensity of 2 to 10 lux is
required to maintain maximum egg production in chickens (Morris and
Owen, 1966).
Ahemeral or non 24 hour light cycles have been used in an
attempt to increase egg production. Success in these ventures
depends on breeding a chicken which is productive on a light cycle
shorter than 24 hours. To date, however, selection for this
trait has not been successful (Foster, 1972; Tucker and Ringer,
1982). Cycles longer than 24 hours have been used to increase egg
weight and shell thickness (Morris, 1978). Long photoperiod cycles
will reduce overall yield but may be useful for commercial producers
if market conditions for production of large eggs are favorable.
Sheep
The effects of photoperiod on production traits in sheep have
been studied extensively. Long days increase growth rate in
wethers and ram and ewe lambs (Forbes et al., 1975, 1979;
8
Schanbacher and Crouse, 1980). Forbes et al. (1979, 1981) observed
that 16L:8D tended to stimulate deposition of muscle in lambs fed
ad libitum or restricted diets. Pelt weights and gut fill of
sheep also increased with longer photoperiods. Lambs exposed to
16 hours light also increased feed intake on both diets in this
experiment. The physiological mechanism by which photoperiod
increases feed intake is unclear. In these studies, however,
metabolic weight increased in animals exposed to 16L and the increase
in feed consumption may have been necessary to maintain the
increased maintenance requirements.
Lambs do not increase body weight due solely to an increase
in feed intake as was observed in chickens (Morris, 1967a). Feed
efficiency was also increased by use of long days (Forbes et al.,
1975, 1979; Schanbacher and Crouse, 1980, 1981). Hackett and Hillers
(1979) did not observe increases in growth rate, feed efficiency,
or carcass composition when lambs were exposed to longer photoperiods.
In this experiment lambs were exposed to night lighting in open
range conditions. The environmental differences between the studies
(open range vs. confinement rearing) may account for the dis-
crepancies observed. Ambient temperature is also important in
regulating feed intake and interactions between photoperiod and
temperature have been observed (Schanbacher et al., 1982). Lambs
exposed to a longer photoperiod at higher temperatures did not
decrease feed intake as much as lambs exposed to a short photoperiod.
Constant photoperiod is not essential for the increased growth
rate of longer photoperiod to be observed. Intermittent photo-
9
periods of 7L:9D:1L:7D were as effective as 16L:8D in growth
stimulation (Schanbacher and Crouse, 1981). This supports the
hypothesis that physiological responses will occur if light occurs
coincident with endogenous daily rhythms in photosensitivity
(Bunning, 1960). This phenomenon will be described in a later
section of this review.
Cattle
Similar to sheep, increased weight gains due to increased
photoperiod have been observed in cattle. Average daily gains of
Holstein heifers in Michigan increased by 10 to 15% when exposed
to longer photoperiods during winter months. Heifers exposed to
continuous photoperiod did not increase weight gains in comparison
to heifers exposed to natural photoperiod (Peters et al., 1978,
1980). Several weeks of exposure to increased photoperiod were
required before body growth increased. Like sheep, heifers ate
more and were more efficient in converting feed to gain when exposed
to longer photoperiods (Peters et al., 1980). Even when intake is
restricted, animals exposed to 16L gained weight faster (Petitclerc
et al., 1981). Similar to results in sheep, 16L caused an increase
in protein deposition compared to 8L (Tucker and Ringer, 1982).
Zinn et al. (1983) observed no difference in average daily gain or
feed intake in prepubertal heifers due to photoperiod; however,
postpubertal heifers grew faster when exposed to a shorter photoperiod.
Postpubertal heifers exposed to 16L had significantly higher feed
intake and carcass protein percentage whereas heifers exposed to
8L had significantly higher carcass fat percentage. The increase
10
in weight gain observed in postpubertal heifers may have been due
to overfeeding as was evidenced by a 1.24 kg average daily gain in
heifers exposed to 8L. Increased photoperiod in this experiment
increased feed intake but did not consistently affect weight gain.
Longer photoperiod may stimulate protein deposition. Animals
exposed to shorter photoperiods did not achieve the same rate of
protein deposition and excess energy intake may have been diverted
into body fat (Tucker, personal communication).
Growth rate was not increased when steers and bulls up to
98 days of age were subjected to 16L (Roche and Boland, 1980;
Tucker, personal communication). However, Tucker (personal
communication) observed a 9% increase in body weight in older
bulls exposed to 16L. A different mechanism of action, possibly
involving the gonads, may be responsible for increased weight
gain in cattle than in sheep. Sheep are short day breeders and
the gonads are most active during periods of decreasing photoperiod.
Longer photoperiods inhibit gonadal development and secretion.
Serum testosterone concentrations were lower in rams exposed to
16L compared to rams exposed to 8L at 22 weeks of age (Schanbacher
and Crouse, 1980). Cattle are not seasonal breeders and photoperiod
has no effect on gonadal development. Serum androgen concentrations
increased at a faster rate as photoperiod increased in cattle
(Tucker, personal communication).
Swine
The stimulation of growth by longer photoperiods may be limited
to ruminants and poultry. In several recent studies with swine, no
11
differences in growth rate or feed efficiency in boars, barrows,
or gilts were observed (Berger et al., 1980; Mahone et al., 1979;
Ntunde et al., 1979). Puberty occurred at an earlier age in young
male pigs exposed to increasing or decreasing photoperiods (Berger
et al., 1980); however, the effect of photoperiod on puberty in
gilts is not known. Ntunde et al. (1979) has found that gilts
exposed to very short photoperiods of 1.5L had delayed puberty
whereas 18L did not stimulate puberty when compared to 9-11L.
Lactation
Milk yield is another economically important trait affected by
photoperiod. Cows in Michigan increased milk yield 6 to 10% without
affecting milk composition when given supplemental lighting during
winter (Peters et al., 1978, 1981). The effect occurred in both
early and late lactation. Dry matter intake increased in cows
receiving supplemental lighting which may have been responsible
for the increased milk yield (Peters et al., 1981). Results from
experiments investigating the effect of photoperiod on lactation
in swine are inconsistent. Mabry et al. (1982) demonstrated an
increase in milk yield and litter weight at weaning in sows exposed
to 16L whereas Greenberg and Mahone (1982) failed to observe an
effect of photoperiod on milk yield. Photoperiod did, however,
have a stimulatory effect on litter weight gain in mice (Sorenson
and Hacker, 1979).
Pineal and Photoperiod
Research has been conducted to investigate the effects of the
12
pineal gland and its products on growth and milk secretion in
laboratory animals. Short photoperiods or blinding are considered
to stimulate secretion of pineal products while long photoperiods
are inhibitory (Reiter, 1977). Blind anosmic rats, in which the
inhibitory effects of the pineal on the neuroendocrine axis appear
to be maximal, grew at a slower rate than intact animals (Reiter,
1974). The effect of the pineal on feed consumption and feed
efficiency must be considered, however, before these results may
be fully interpreted. Neither mammary development (Mishkinsky et al.,
1966) nor lactation (Nir et al., 1968) were affected by
pinealectomy in rats maintained on 12L:12D photoperiods. Mizuno
and Sensui (1970) also observed no effect of pinealectomy on
litter weights in rats exposed to 14L:10D on day 16 postpartum.
The validity of these experiments has been questioned, however,
by Reiter (1977) who suggests that animals exposed to more than 12
hours of light per day are "physiologically pinealectomized". The
effect of the pineal on lactation in rats, therefore, is subject to
further interpretation.
Sorenson and Hacker (1979) recently studied the effects of
purified bovine pineal extract and light duration on lactation in
mice. Litter weights of mice exposed to 16L were increased as
compared to controls (8L). If photoperiod influences lactation
through its effects on tht.. pineal an interaction between light
duration and administration of pineal extracts would have been
expected. The lack of interaction between photoperiod and pineal
products observed in this experiment may indicate that the pineal
13
is not an important part of the control mechanism and that some
other light sensitive stie may be responsible for increases in milk
yield due to photoperiod.
The administration of pineal extracts as well as the pineal
indoles, serotonin and melatonin, lowered the milk yield curve in
rabbits (Shani et al., 1971); however, Mizuno and Sensui (1970)
found no inhibitory effect of melatonin on litter weight gain in
rats. Again, long photoperiods were used and animals may have been
physiologically pinealectomized. Serotonin has an inhibitory
effect on oxytocin release in response to suckling (Mizuno et al.,
1967) thus suppressing milk yield. In another study, Mizuno and
Sensui (1970) did not observe an effect of pinealectomy or melatonin
administration on the amount of residual milk in rats. Conclusions
on the effect of the pineal gland on milk ejection and lactation
await further investigation.
Pineal extracts have been evaluated for their effects on
the lactogenic hormone PRL. The primary site of action of the
pineal is considered to be the brain (Reiter, 1973). Pineal products
may also act either at the hypothalamo-hypophyseal axis or directly
on the anterior pituitary. Bovine pineal extracts both increased
and decreased PRL secretion from rat hemipituitaries cultured
in vitro (Blask et al., 1976). Similarly, in vivo administration of
bovine pineal extracts elevated (Blask et al., 1976) and suppressed
(Ebels and Benson, 1978) plasma PRL levels in rats. Recent
experiments in blind anosmic rats indicate that the pineal inhibits
PRL synthesis, storage, and release (Leadem and Blask, 1982).
14
Prolactin and Photoperiod
The effects of PRL in mammals are many. Specific effects
of interest in this review are growth and lactation, two traits
also affected by photoperiod.
Prolactin is anabolic in some systems (Nicoll, 1980). Growth
was depressed in sheep immunized against PRL (Ohlson et al.,
1981). But treatment with ergot alkaloids, which also decrease
PRL levels substantially, did not affect growth (Ravault et al.,
1977). Animals in this experiment were exposed to natural photo-
periods during seasons of both increasing and decreasing photoperiods.
The effects of suppression of PRL by ergot alkaloids on growth
of animals exposed to constant long or short photoperiods has not
been studied.
The pineal gland is also important. Pinealectomy inhibits
normal fluctations in blood PRL concentrations in response to
photoperiod (Brown and Forbes, 1980); pinealectomized lambs did
not grow faster when exposed to longer photoperiods.
Prolactin affects milk production by stimulating several key
biochemical processes during lactogenesis in cattle (Akers et al.,
1981). In addition, PRL is necessary for the maintenance of
lactation in the bovine although it is not thought to be a limit-
ing factor (Tucker, 1979).
Serum concentrations of PRL fluctuate seasonally in cattle
(Bourne and Tucker, 1975), sheep (Pelletier, 1973) and goats
(Hart, 1975). Length of photoperiod is positively correlated
with serum PRL concentrations in bulls (Leining et al., 1979).
15
Serum PRL concentrations change more quickly in response to
decreasing photoperiod than to increasing photoperiod (Bourne and
Tucker, 1975). Abrupt increases in photoperiod from 8 hours of
light to 16 to 20 hours of light per day increased PRL concen-
tration after one week and maximal PRL concentrations were
attained at 9 weeks (Leining et al., 1979). Continuous light
resulted in decreased PRL levels similar to that observed under a
natural photoperiod. Experiments using gradual and abrupt changes
in photoperiod have yielded similar results in sheep (Pelletier,
1973; Ravault and Ortavant, 1977). Photoperiods of 15L did not,
however, increase PRL levels in swine when compared to natural
photoperiods of 8L (Hoagland et al., 1981).
Components of light also have been studied in relation to
PRL release. Most experiments studying the effects of photo-
period on PRL in the bovine have been conducted using cool
white fluorescent lights with high intensity (e.g. 600-800 lux)
(Bourne and Tucker, 1975; Leining et al., 1979; Peters et al.,
1981). The threshold of light intensity necessary to elicit
PRL release remains to be determined. A longer photoperiod
(16 hours) utilizing high intensity fluorescent lighting (200 to
300 lux) elicited increased PRL secretion as compared to a
shorter photoperiod (9 to 11 hours) utilizing low intensity indirect
natural light (35 to 40 lux)(Peters and Tucker, 1978). Various
wavelengths of light studied have not been more or less effective
than white light in eliciting PRL release in response to photo-
period (Leining et al., 1979).
16
Prolactin levels are affected by other environmental conditions.
Increased ambient temperature will increase PRL concentration
in cows. Peters and Tucker (1978) observed wide fluctuations in
serum PRL in heifers exposed to 16L:8D. Increases and decreases
in PRL concentration were syndhronized with changes in ambient
temperature. Tucker and Wettemann (1976) observed lower
basal PRL levels in heifers exposed to 4.5°C when compared
to 21°C and 32°C. Prolactin response to thyrotropin releasing
hormone (TRH) injection was also decreased in heifers exposed to
21°C when compared to heifers exposed to 32°C and was not evident
in heifers exposed to 4.5°C. Prolactin was not affected by relative
humidity. The PRL response to temperature supersedes any
response to photoperiod. No differences were observed in serum
PRL concentration in heifers exposed to natural, 16L:8D, or
24L:OD when ambient temperature approached 0°C (Peters et al.,
1980). Thus the effect of photoperiod on PRL and its relation-
ship to growth and lactation is questionable. Increased weight
gains in response to 16L:8D persisted throughout winter in Michigan
(Peters et al., 1978, 1980) and milk yields did not decrease during
exposure to cold (Petitclerc et al., 1981).
Stressful stimuli such as pain will elicit increases in PRL
secretion in cattle (Tucker, 1971), but not swine (Hoagland
et al., 1981). Feeding also has been implicated in the release of
PRL in the bovine (McAtee and Trenkle, 1971) and ad libitum
feeding causes increased serum PRL levels in sheep (Forbes
et al., 1975). Interpretation of PRL levels must be made carefully
17
therefore, as many factors contribute to its secretion.
Photosensitivity
Recently, several experiments have tested the theory of
Bunning (1960) that animals measure time from the degree of coin-
cidence of their daily endogenous rhythm and the external photo-
period. Period of uninterrupted light or uninterrupted dark may
be the signals which entrain the cycle of endogenous photosensitivity
(Pittendrigh and Minis, 1964).
Schanbacher and Crouse (1981) exposed ram lambs to short
(8L:16D), long (16L:8D), and split (7L:9D:1L:7D) photoperiods.
Increased weight gains and feed intake were observed in animals
exposed to the long and split photoperiod. Light was proposed to
be the Zeitgeber for feed intake. The exposure to 1 h of light
16 h after dawn was observed to be in the photosensitive phase
and physiologic responses such as increased weight gain and feed
intake occurred, even though the total photoperiod was only 8 h.
Ravault and Ortavant (1977) and Thimonier et al. (1978) used
Bunnings theory in investigating photosensitivity and PRL
secretion in rams. A split photoperiod (7L:9D:1L:7D) again was as
effective as 16L:8D in eliciting increased PRL secretion.
Insertion of the one hour pulse of light at other times of the day
was ineffective in stimulating PRL secretion. A normal diurnal
rhythm of PRL secretion is present in sheep (Ravault and
Ortavant, 1977) with PRL secretion increasing when lights are
turned off. No such endogenous rhythm is present in cattle
18
although a diurnal rhythm of photosensitivity has been observed
(Petitclerc et al., 1983). A 6L:8D:2L:8D photoperiod was as
effective as 16L:8D in increasing PRL secretion in bulls.
a 2 h pulse of light between 14 to 16 and 20 to 22 hours after
dawn increased PRL levels although light at 20 to 22 hours
after dawn was much less effective. Further experimentation with
photosensitivity and its application to production traits is
important to the animal industry. Significant savings, as those
observed in the poultry industry, may be realized through the
manipulation of photoperiod.
Running Head: Photoperiod and Milk Production
EFFECT OF PHOTOPERIOD ON MILK PRODUCTION
AND PROLACTIN IN HOLSTEIN DAIRY COWS'
J.M. Marcek and L.V. Swanson2
Department of Animal Science
Oregon State University
Corvallis, OR 97331
Key Words: Photoperiod, 4% fat corrected milk, Prolactin, TRH
'Technical Paper No.
2Reprint requests.
, Oregon Agr. Exp. Station.
19
20
ABSTRACT
Fourteen multiparous Holstein cows were paired by stage of
lactation and previous years milk yield and 14 Holstein first-
calf heifers were paired by stage of lactation. One member of
each pair was assigned to a 24L:OD or an 18L:6D photoperiod for
16 wk during winter 1981 (Experiment 1). A similar experiment
comparing natural photoperiod (9-12 h light/day) and 18L:6D was
conducted for 9 wk during winter 1982 (Experiment 2) in which 24
Holstein cows and 22 Holstein first-calf heifers were paired and
assigned to groups as in the first experiment. Animals were
housed in a free stall barn open on 2 sides. High pressure sodium
vapor lamps provided light intensity at cow eye level of 254±26 lux
during the day and 132±9 lux at night. In Experiment 1, concen-
tration of serum prolactin in response to thyrotropin releasing
hormone (33 pg/100 kg body weight) was measured in 5 animals from
each group. Prolactin response to thyrotropin releasing hormone
or saline was tested in 10 animals in each group in Experiment 2.
Photoperiod had no effect on 4% fat corrected milk (FCM) in either
age group in Experiment 1 although cows in the 18L:6D group
averaged 2% higher persistenly in 4% fat corrected milk. Cows
in the 18L:6D group were 7% more persistent in 4% fat corrected
milk in Experiment 2 as compared to cows exposed to a natural
photoperiod. Persistency in heifers was unaffected by photo-
period in this experiment. Basal concentration of serum prolactin
was not affected by either age or photoperiod in Experiment 1
(21.3±3.3 ng/ml). Peak concentration of serum prolactin after
21
thyrotropin releasing hormone injection was not affected by
photoperiod in the heifer group, but cows exposed to 18L:6D
had significantly higher concentrations of serum prolactin after
thyrotropin releasing hormone injection than cows exposed to
24L:OD (560±133 vs. 229±54 ng/ml). Basal concentration of serum
prolactin in Experiment 2 was similar in thyrotropin releasing
hormone and saline-injected animals (26.3±3.1 ng/ml) but was lower
in cows than in heifers (17.1±2.0 vs. 35.5±5.0 ng/ml). In
Experiment 2 saline injection did not elicit a prolactin increase,
nor were there any differences in concentration of serum prolactin
after thyrotropin releasing hormone stimulation due to either
photoperiod or age. Weight gain of cows did not differ due to
photoperiod in Experiment 1 although heifers exposed to 24L:OD
gained more weight than those exposed to 18L:6D. Cows in Experiment
2 gained significantly more weight when exposed to 18L:6D. No
difference in weight gain due to photoperiod was observed for heifers
in Experiment 2. We conclude that milk yield in mature cows can
be increased by using supplemental lighting during winter months
when compared to natural photoperiod. No difference in milk yield
between 18L:6D and 24L:OD were observed. Prolactin does not
appear to be involved in the mechanism of action of photoperiods
stimulation of milk yield.
23
18L:6D and 24L:OD. The effect of these photoperiods on con-
centrations of serum PRL at rest and after TRH stimulation also
was studied.
24
MATERIALS AND METHODS
Experiment 1
Fourteen multiparous Holstein cows and 14 Holstein first-
calf heifers were used. Cows were paired according to previous
year's production and days in lactation (38 to 207 days), whereas
heifers were paired according to days in lactation (31 to 197 days).
One member of each pair was assigned randomly to 18L:6D and the
other to a 24L:OD photoperiod. All animals were on a 24L:OD
photoperiod prior to the experiment. Cows were housed in a free
stall barn open on the north and south sides. Treatment groups
were separated from each other by a length of 28 m within the barn.
Mean intensity of light at cow eye level was 2541-26 lux during the
day and 132±9 lux at night. Identical completely mixed rations
consisting of corn silage, alfalfa hay cubes, whole cottonseed,
and a 16% crude protein dairy concentrate were fed once daily to
cows and heifers in their respective treatment groups.
Cows and heifers were assigned to treatment groups in December
1981 and the experiment was conducted for 16 wk through April 1982.
All animals were maintained on a 24L:OD photoperiod before the
beginning of the experiment. Milk yield and milk composition
(fat, protein) were monitored weekly. All animals were weighed
on two consecutive days each month during the experiment.
To determine if photoperiod had an effect on pituitary PRL,
5 animals from each group were selected randomly for a TRH challenge
experiment. Cows were locked in stanchions and feed was removed
2 h prior to the experiment. Blood samples were collected via tail
25
venipuncture at -30, -15, 0, +5, +10, and +15 min relative to
intravenous injection of a standard dose (33 ug/100kg BW) of TRH
(Sigma Chemical Co., St. Louis, Mo.). Samples were allowed to
clot at room temperature, then centrifuged and the serum decanted.
Serum was stored at -20°C until assayed for PRL content by double
antibody radioimmunoassay (5). NIH-P-B3 was used as the reference
standard.
Experiment 2
A similar experiment was conducted beginning November 1982
for 9 wk through January 1983. For 2 months prior to the start
of the experiment, cows at the Oregon State University Dairy
Center were maintained on a natural photoperiod schedule. Twenty-
four Holstein cows and 22 Holstein first-calf heifers were paired
as in the previous experiment. One member of each pair was assigned
at random to a natural photoperiod and the other to an 18L:6D
photoperiod at 10 days postpartum or later. Cows ranged from 10
to 159 days and heifers ranged from 35 to 283 days in lactation
at the beginning of the experiment. Natural photoperiod during
the experimental period ranged from 9 to 11.5 h light per day.
Housing and feeding schedules were consistent with the previous
experiment. Milk yield, milk composition, and cow weight were
monitored as in Experiment 1.
The effect of photoperiod on PRL was studied as in the first
experiment except that 5 saline-injected animals were included
in each group as controls. Blood samples were collected at -30,
-15, 0, +10, +15, and +20 min relative to administration of the
26
standard dose of TRH.
Persistency of milk yield is defined as the percentage of a
current month's yield relative to the previous month's yield.
Statistical analysis of milk yield, milk composition, and cow
weight data was accomplished using split-plot analysis of variance.
Basal concentrations of PRL in serum and differences between basal
levels and peak TRH-induced concentrations of PRL in serum were
analysed by analysis of variance.
27
RESULTS AND DISCUSSION
Milk yield and 4% FCM were not changed due to altered photo-
period in the heifers for Experiments 1 and 2, respectively,
(Figures 1 and 2) perhaps due to the higher persistency normally
observed in heifers (1). Heifers maintained average monthly
persistencies of 98 to 100% in milk yield and 98 to 101% in 4%
FCM during the experiments.
Milk yield (Figure 3) and 4% FCM were not significantly
different in cows exposed to 18L:6D compared to 24L:OD (Experiment 1)
although monthly persistency of milk yield was 2% higher in the
18L:6D group.
A significant photoperiod by week interaction (P<.01) was
observed in 4% FCM when 18L:6D was compared with natural photo-
period (Figure 4), whereas milk yield did not differ (Experiment 2).
Cows exposed to 18L:6D maintained monthly persistencies of 99%
in 4% FCM while those exposed to natural photoperiod averaged 92%.
Cows exposed to 18L:6D had average monthly persistency of 101%
in milk yield whereas those exposed to natural photoperiod averaged
97% persistency. These results are in agreement with Peters et al.,
(9, 10) who observed that cows exposed to longer photoperiods
during winter months responded with an increase in milk yield;
however, in the present experiment the increase in milk yield was
not statistically significant.
In these experiments, 18L:6D increased milk yield in mature
cows in comparison to a natural photoperiod. Continuous lighting
was as effective in maintaining persistency of milk yield as
28
18L:6D, however direct comparisons between the results of Experiments
1 and 2 cannot be made because they were conducted in different
years and animals were maintained on different control photoperiods
prior to beginning the experiments.
Mechanisms by which photoperiod stimulates increased milk
yield are not known. One possibility is the effect of photoperiod
on feed intake. Peters et al. (9) observed an increase in feed
intake when lactating cows are exposed to longer photoperiods.
This would be an economical method to increase milk yield since
additional feed consumed would exceed maintenance requirements
and be available for milk synthesis. Other experiments indicate
that heifers increase feed intake when exposed to longer photo-
periods but not when exposed to continuous lighting (8, 10). In
a concurrent behavioral study during Experiment 1, Tanida et al.
(14) observed no difference in total time spent eating in cows
exposed to either 18L:6D or 24L:OD. Feeding patterns did not
differ from what previously has been observed for cattle exposed
to natural photoperiod who exhibit diurnal rhythms, eating more
during daylight hours and having peaks of eating activity both in
the morning and afternoon (2). In contrast, Zinn et al. (18)
concluded that lights on, lights off, and presentation of fresh
feed increased feeding activity in prepubertal heifers. Heifers
exposed to short photoperiods began eating about 2 h before lights
on, indicating that entrainment to the light cycle had occurred.
Hafez and Bouissou (4) have suggested that feeding behavior responds
to the influence of ambient temperature as well as to other
29
environmental conditions. It is possible that, if animals were
placed in an environmentally controlled chamber, photoperiod
would be the key Zeitgeber for entrainment of feeding behavior.
In natural barn conditions, however, additional factors such as
daily fluctuations in temperature, humidity, presentation of feed,
and milking activity may influence feeding behavior.
The intensity of light used in this experiment was lower than
that used previously (9, 10). Stevenson et al. (13) observed that
milk production increased linearly in sows as intensity of light
increased. The interaction of light intensity and duration may
also be important in the bovine and warrants further examination.
The effect of photoperiod on percent fat and percent protein
in milk was examined. In Experiment 1, milk samples were analysed
during weeks 1 to 12 of the experiment but data from week 1 were
not included in the analysis due to an error in sampling procedure.
Percent milkfat and percent protein were not affected by photo-
period in heifers in Experiment 2 or cows in Experiment 1.
Differences did exist in the other two groups. A significant
photoperiod by week interaction was observed for percent milkfat
(P<.05) and percent protein (P<.01) in heifers in Experiment 1.
Both traits increased at a more rapid rate during weeks 2 to 12 of
the experiment in heifers exposed to 18L:6D. Significant inter-
actions also were observed for percent milkfat (P<.05), kg milkfat
(P<.01), and percent protein (P<.05) in cows in Experiment 2.
Percent milkfat and kg milkfat (Figure 5) decreased at a slower
rate in cows exposed to 18L:6D as compared to cows exposed to
30
natural photoperiod. This contributed to increased persistency
in 4% FCM and to the interaction observed in kg milkfat. Percent
protein, on the other hand, decreased at a faster rate in cows
exposed to 18L:6D.
We believe that the differences in percent milkfat and
percent protein observed in this experiment are not biologically
important because overall yields of milkfat and protein were not
affected. The one instance in which kg milkfat was affected may
have been due to the increase in milk yield observed. Other
researchers reported no difference in percent milkfat in response
to photoperiod (9). Variations in percent milkfat and percent
protein throughout the lactation are normal (12). Both components
decrease during the beginning of lactation, level off, and then
gradually increase in the latter half of lactation. Many other
factors are also responsible for variation in milk composition
including season, age, stage of lactation, pregnancy, mastitis,
feeding and management practices, as well as individual cow
variation (6). Further examination of our data revealed that in-
herent differences between cows may have been responsible for the
differences observed, since cows were not paired on milk composition
traits at the beginning of the experiments.
Data from the PRL experiments in 1981 are presented in Table 1.
No differences in basal PRL concentration due to photoperiod or
age were observed although cows tended to have higher basal PRL
levels (P=.10) than heifers (27±6 vs. 15±2 ng/ml). Peak PRL levels
after TRH injection were significantly higher (P<.05) in cows
31
exposed to 18L:6D as compared to cows exposed to 24L:OD but did
not differ for the heifers. In the 1982 experiment basal PRL
concentration in saline-injected animals did not differ from basal
PRL levels observed for TRH-injected animals; therefore, the data
were pooled for analysis. Peak PRL concentration after saline
injection was not included in the analysis since saline injection
did not elicit an increase in serum PRL. Basal PRL levels in this
experiment did not differ due to photoperiod although serum PRL
concentrations were higher (P<.01) in heifers than in cows
(Table 2). No differences due to photoperiod or age were observed
in PRL concentration after TRH stimulation.
Endogenous hormone secretion has been hypothesized to be one
mechanism by which photoperiod influences milk yield. Several
hormones are involved in lactogenesis and galactopoiesis in the
bovine. These include placental lactogen, PRL, growth hormone,
glucocorticoids, and thyroxine (15). Of these, PRL is the most
responsive to changes in photoperiod. Peters et al. (9) observed
increased basal concentrations of PRL and increased concentrations
of PRL after TRH stimulation in lactating cows exposed to 16L:8D
as compared to cows exposed to 8L:16D. Growth hormone and thyroxine
are not influenced by photoperiod (7, 8, 9). Some evidence that
glucocorticoid concentration is negatively correlated with photo-
period has been reported in some (7) but not all experiments
(8, 9). Vanjonack and Johnson (17) observed that high producing
cows had higher glucocorticoid levels at lower temperatures but
that corticoid levels decreased faster in high producing cows at
32
higher temperatures. Prolactin is positively correlated with
temperature (16) and low temperatures (approximately 0°C) over-
ride any photoperiod-induced increase in PRL concentration (8).
In our experiment no consistent differences in PRL concentration
due to photoperiod were observed. This is contrary to that observed
previously (7, 8, 9) although the milder climate in which the
experiment was conducted and light source (although wavelength
of light has not been observed to affect PRL concentration (7))
may account for these differences. We do not believe temperature
was an important factor as it was consistent (10°C) throughout
the sampling periods. The lower intensity of lighting may have
accounted for the decreased PRL response to photoperiod, although
Peters and Tucker (11) used low intensity lighting (i.e. 300 lux)
and observed an increase in serum PRL concentration in heifers
in response to longer photoperiod. Because of the nonspecific
nature of prolactin release, other factors of which we were not
aware may have produced the significant differences observed.
The inconsistencies observed in serum concentrations of PRL do
not seem to be related to the increases observed in milk yield.
This adds further evidence that prolactin is not a limiting factor
for milk yield in the bovine.
First-calf heifers, but not cows, exposed to 24L:OD gained
weight faster (P<.05) than those exposed to 18L:6D in Experiment 1
(Table 3). There were no differences in heifers in Experiment 2.
Cows in Experiment 2 gained significantly more weight (P<.01) when
exposed to 18L:6D. Peters et al. (9) did not detect differences
33
in weight gain due to photoperiod in lactating cows. We may have
encountered genetic differences or environmental factors such as
competition for bunk space or competition between cows. Diets,
however, were the same for the two heifer and two cow groups.
From these data we conclude that increased photoperiod during
winter months stimulates milk yield in cows but not in first-calf
heifers. Milk yield, however, did not differ in cows or heifers
exposed to continuous lighting as compared to those exposed to
18L:6D. Increased percentages of protein and fat were observed
in some experiments; however, total fat and protein yields did
not differ.
Serum PRL concentration did not increase in response to
photoperiod as had been observed previously. This may have been
due to different climatic conditions or different intensity of
lighting. These data do not indicate that PRL is responsible for
the increase observed in milk production due to photoperiod.
34
Table 1. Serum prolactin concentration (ng/ml) in cows and heifers at rest(basal) and after thyrotropin releasing hormone (TRH) challenge(33 ug/100 kg) Experiment 1.
Basal
TRHStimulateda
24L:OD 18L:6D 24L:OD 18L:6D
Cows 23+6bc 31±11c 229±54d 560±133e
Heifers 17±3c 14±2c 390±65d
390±86d
aData represent peak concentration minus basal concentration
bMean ± SE
c,d,eMeans in rows not sharing a common superscript differ (P<.05)
Table 2. Serum prolactin concentration (ng/ml) in cows and heifers atrest (basal) and after thyrotropin releasing hormone (TRH)challenge (33 ug/100 kg) Experiment 2.
BasalTRH
Stimulateda
Natural Natural
Photoperiod 18L:6D Photoperiod 18L:6D
35
Cows 14±2b 20±3 584±113 620±90
Heifers 41±7 30±7 426±145 616±143
aData represent peak concentration minus basal concentration
bMean ± SE
36
Table 3. Mean monthly body weights (kg) of cows and first-calf heifers exposedto various photoperiods.
Experiment 1
Cows
Month 24L:0Da 18L:6Da
Heifers
24L:ODb
18L:6Dc
1 666±12d
634±20 616±20 587±11
2 672±14 635±19 621±21 583±12
3 673 ±11 639±20 631±22 587±11
Experiment 2
Cows Heifers
Natural Natural
Month Photoperiod 18L:6Db
Photoperiod 18L:6Dc
1 667±22 658±13 631±10 601±6
2 668±20 664±14 642±9 602±7
3 669±20 686±16 659110 629±8
a,b,cPhotoperiod treatments within experiments not sharing a common superscript
differ (P<.05) over time.dMean ± SE
37
FIGURE 1. Mean weekly milk yields for heifers in Experiment 1exposed to two photoperiods (18L:6D and 24L:OD).Straight lines represent regressions computed fromthe data.
35
251
, \
- --4:V --\-- ----III
FIGURE I
24L:OD
I a a a a a I I I
0 2 4 6 8WEEKS
I0 12 14 16
39
FIGURE 2. Mean weekly four percent fat corrected milk (4% FCM)for heifers in Experiment 2 exposed to two photo-periods (18L:6D and natural). Straight lines rep-
resent regressions computed from the data.
30
25
40
Natutol Photoperiod
FIGURE 2
2 4
18L.:61:10
WEEKS6 8
41
FIGURE 3. Mean weekly milk yield for cows in Experiment 1 exposed
to two photoperiods (18L:6D and 24L:OD). Straightlines represent regression lines computed from the data.
N co0
\I
N 41 co
m m c
ox co
0 TT
)
71%
Z17
i
KG
MIL
K/D
AY
ca 0co cs
11
i1
1i
1i
i1
I
-*I
G) C 23 rn cg
1
43
FIGURE 4. Mean weekly 4% FCM for cows in Experiment 2 exposed totwo photoperiods (18L:6D and natural). Straight linesrepresent regressions computed from the data.
40
30
0 2 4WEEKS
6 8
45
FIGURE 5. Mean weekly kilograms milkfat per day for cows inExperiment 2 exposed to two photoperiods (18L:6D andnatural).
1.8
1.6
1.0
0.8
Vi5VGC)--C
-.0-- N
Natural Photoperiod
FIGURE 5
,o--0
I t I t i t t i0 2 4 6 8
WEEKS
47
REFERENCES
1 Campbell, J.R., and R.T. Marshall. 1975. The Science of Pro-viding Milk for Man. pp 249. McGraw-Hill Book Company, New York.
2 Chase, L.E., P.J. Wangsness, and B.R. Baumgardt. 1976. Feed-ing behavior of steers fed a complete mixed ration. J. DairySci. 59:1923.
3 Convey, E.M., H.A. Tucker, V.G. Smith, and J. Zolman. 1973.Bovine prolactin, growth hormone, thyroxine, and corticoidresponse to thyrotropin-releasing hormone. Endocrinology92:471.
4 Hafez, E.S.E., and M.F. Bouissou. 1975. The behaviour ofcattle. In: E.S.E. Hafez (Ed.) The Behavior of Domestic Animals.(3rd Ed). pp 532. Bailliere Trindall, London.
5 Koprowski, J.A., and H.A. Tucker. 1971. Failure of oxytocinto initiate prolactin or LH release in lactating dairy cattle.J. Dairy Sci. 54:1675.
6 Laben, R.L., R. Shanks, P.J. Berger, and A.E. Freeman. 1982.
Factors effecting milk yield and reproductive performance.J. Dairy Sci. 65:1004.
7 Leining, K.B., R.A. Bourne, and H.A. Tucker. 1979. Prolactinresponse to duration and wavelength of light in prepubertalbulls. Endocrinology 104:289.
8 Peters, R.R., L.T. Chapin, R.S. Emery, and H.A. Tucker. 1980.
Growth and hormonal response of heifers to various photoperiods.J. Anim. Sci. 51:1148.
9 Peters, R.R., L.T. Chapin, R.S. Emery, and H.A. Tucker. 1981.
Milk yield, feed intake, prolactin, growth hormone, glucocorti-coid, response of cows to supplemental light. J. Dairy Sci.64:1671.
10 Peters, R.R., L.T. Chapin, K.B. Leining, and H.A. Tucker. 1978.
Supplemental lighting stimulates growth and lactation in cattle.Science 199:911.
11 Peters, R.R., and H.A. Tucker. 1978. Prolactin and growthhormone response to photoperiod in heifers. Endocrinology
103:229.
12 Rook, J.A.F., and R.C. Campling. 1965. Effect of stage oflactation on the yield and composition of cows milk. J. Dairy
Res. 32:45.
48
13 Stevenson, J.S., D.S. Pollmann, D.L. Davis, and J.P. Murphy.1983. Influence of supplemental light on sow performanceduring and after lactation. J. Anim. Sci. 56:1282.
14 Tanida, H., L.V. Swanson, and W.D. Hohenboken. 1983. Arti-ficial photoperiod and behavior in dairy cows. J. Anim. Sci.57:Suppl. 1, 142.
15 Tucker, H.A. 1979. Endocrinology of Lactation. Seminarsin Perinatology 3:199.
16 Tucker, H.A., and R.P. Wettemann. 1976. Effect of ambienttemperature and relative humidity on serum growth hormone andprolactin in heifers. Proc. Soc. Exp. Biol. Med. 151:623.
17 Vanjonack, W.J., and H.D. Johnson. 1975. Effect of heat andmilk yield on bovine plasma glucocorticoid levels. Proc. Soc.Exp. Biol. Med. 148:970.
18 Zinn, S.A., L.T. Chapin, and H.A. Tucker. 1983. Does photo-period and time of feeding affect growth and eating pattern ofheifers? J. Anim. Sci. 57:Suppl. 1, 217.
49
CONCLUSIONS
This and other studies have demonstrated that 16 to 18 h
light per day increase milk yield in mature dairy cows when compared
to natural photoperiod. Cows exposed to continuous lighting in
this experiment did not differ in milk yield from cows exposed to
18 h light. Further study is needed to determine the optimum
photoperiod as well as minimum intensity required for maximum
stimulation of milk yield in the dairy cow. Recent experiments
using split photoperiods in bulls indicate a photosensitive phase
for PRL release in the bovine (Petitclerc et al., 1983). Research
investigating the use of a split photoperiod to stimulate milk
production should also be conducted.
The mechanism by which photoperiod stimulates milk yield is
not understood. Results of this experiment add further evidence
that PRL is not responsible for the increases observed. The effects
of the pineal on PRL and lactation have just begun to be studied.
This endocrine organ may have significant impact on lactation
through products which have not, as yet, been identified. The effects
of photoperiod on other parts of the brain should be examined to
determine if other light sensitive areas of the brain exist, and if
so, what impact they may have on physiologic processes such as
growth and lactation.
The manipulation of photoperiod and the resulting increase in
milk yield are of potential benefit to the dairyman. Electricity
for one 400 watt high pressure sodium vapor lamp would cost the
50
dairyman $49.70 per year if used for 18 h per day for six months
each year (based on March 1983 electricity prices for the Northwest
(3.780/kwh). Each lamp provides sufficient light to illuminate
251 square m at approximately 100 lux if positioned 6.5 m above the
barn floor. Each cow requires 8.7 square m of space, including
free stall, cow alley, feed manger, and feed alley space. One
fixture therefore would provide enough light for 29 cows.
As an example, assume that Joe Farmer has 100 cows with a
rolling herd average of 6306 kg milk with 3.5% butterfat. His
cows, on the average, are producing 5833 kg 4% FCM per year.
If, by providing supplemental light, 4% FCM is increased by 7%
as observed in our experiment, each cow will produce 204 kg more
4% FCM if increased lighting is effective for 6 months. At
current milk prices of $13.50 per cwt (29.760 per kg) and 170 fat
differential (for each 0.1% change from 3.5%) per cwt (.3750 per
kg), income would increase by $64.55 per cow. Approximately 30%
of most herds are first calf heifers and would not benefit from
the additional light. So additional income per year for the 70
mature cows would be $4518. Additional costs per year would include
the four lamps ($165 per lamp over 10 years expected life = $66
per year) and electricity ($49.70 per lamp X four lamps = $198.80),
giving a total cost per year of $264.80. Net additional income
would be $4253.20 or $42.54 per cow and a return per dollar invested
of $16.06. Additional savings in electricity may be realized if
future experiments using intermittent lighting, or light for 1-2
hours at specific periods of time after dawn, prove successful.
51
Our experiment has provided information useful to the dairy
farmer in Oregon. Providing cows with supplemental photoperiod can
provide substantial increases in income, which, in view of the current
milk surplus, would allow the dairyman to decrease herd size and
thus operating costs.
52
BIBLIOGRAPHY
Akers, R.M., D.E. Bauman, A.Y. Capuco, G.T. Goodman, and H.A.Tucker. 1981. Prolactin regulation of milk secretion andbiochemical differentiation of mammary epithelial cells inperiparturient cows. Endocrinology 109:23.
Barott, H.G., and E.M. Pringle. 1951. Effect of environment ongrowth and feed and water consumption of chickens. IV. Theeffect of light on early growth. J. Nutr. 45:265.
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APPENDIX
59
APPENDIX 1
Feed Intake
Feed intake data for Experiments 1 and 2 are presented in
Appendix Table 1. The amount of feed cows received was recorded
daily and amount of feed refused was recorded once weekly from
which total feed intake per group was calculated. Number of cow
days per group per week was used to calculate mean intake per cow
per day.
Data were analysed within experiments using a two by two
factorial design with photoperiod and age as the main effects. As
expected, cows ate significantly more (P<.01) than heifers in both
experiments. This can be attributed to higher metabolic body weights
and feed requirements of the cows. A significant treatment by age
interaction (P<.01) was observed in Experiment 2. Cows exposed to
18L:6D ate less than cows exposed to natural photoperiod (43.0±0.6 vs.
44.4±0.7 kg feed/day) whereas heifers exposed to 18L:6D ate more
than heifers exposed to natural photoperiod (40.3±0.6 vs. 38.3±0.5 kg
feed/day).
Regression analysis indicated that cows in Experiment 1 exposed
to 24L:OD increased feed intake while those exposed to 18L:6D de-
creased weekly feed intake over the length of the experiment
(Appendix Figure 1). Heifers in Experiment 2 ate less when ex-
posed to 18L:6D and increased feed consumption when exposed to
natural photoperiod (Appendix Figure 2).
Interpretation of these data must be made with care. In both
60
experiments dry matter intake was not calculated. Corn silage was
stored in a bunker silo which was partially open to environmental
conditions. During periods of heavy rains, dry matter in corn
silage, and therefore in the total ration, decreased. Other
commodities used in the ration were not subject to these open
conditions and maintained uniform dry matter.
Another important factor in interpreting these data is that
although experimental animals remained in the alleys for the length
of the experiment, nonexperimental animals were moved in and out
of the alleys at various times. Competition between cows and
competition for feed manger space therefore, changed from time to
time throughout the experiment. Prior to being introduced into
the groups, new cows were not always exposed to the same photo-
period as animals in the alley. The effect of photoperiod on feed
intake in these new animals would not be the same as the effect on
experimental animals because acclimation time to the new photo-
period was different. Therefore, it is not possible to draw firm
conclusions on the effect of photoperiod on feed intake from these
data.
Estrus detection during Experiment 1 was conducted using both
visual observation by experimenters and herd staff and KaMar Heat-
mount Detectors (KaMar, Inc., Steamboat Springs, CO). A summary
of the accuracy of the KaMar heat detectors is presented in
Appendix Table 2. Estrus was determined by visual observation
(e.g. standing to be mounted, mucus discharge), rectal palpation
at time of insemination, and subsequent rectal palpation of pregnancy.
61
Sixty-six percent of all cows in estrus had KaMar aids activated.
Thirty-seven percent of all KaMars activated were false positive.
Eighty-eight percent of first calf heifers in heat had KaMar aids
activated and 55% of all KaMars activated in this age group were
false positive. The increased activity of the younger animals
may account for the difference observed between age groups.
Other factors which may have affected the accuracy of the estrus
detection aids include the steep slope of the barn floor (4°),
which may have deterred the cows willingness to mount, and the
reproductive condition of the animals. This herd had a relatively
high incidence of cystic ovaries as diagnosed by rectal palpation
(39% of cows and 11% of heifers). Nymphomania and anestrus are
clinical signs of cystic ovaries and would affect the number of
false positive readings and total number of cows in observed
estrus, respectively. Nineteen percent of cows with activated
KaMars and 24% of heifers with activated KaMars were not observed
in estrus visually. Accuracy of estrus detection was determined
here by interval from previous estrus, or subsequent pregnancy
from breeding. These results indicate that KaMar estrus detection
aids can be used to assist in estrus detection, however due to
the high number of false positive readings, they should not be
used as the only method of estrus detection.
62
Appendix Table 1. Mean daily feed intake (kg feed as fed/cow/day)for Cows and Heifers in Experiment 1 and 2.
Experiment 1
Week
Cows
24L:OD 18L:6D
Heifers
24L:OD 18L:6D
1 44.0 42.6 46.9 40.52 46.4 46.5 40.3 37.53 45.5 45.3 41.9 40.84 44.5 51.4 44.5 45.05 41.1 45.3 38.8 42.96 40.7 40.0 39.6 44.37 43.8 41.4 41.8 38.58 42.9 42.1 40.1 38.89 44.5 42.2 40.3 37.3
10 42.8 39.3 41.4 37.011 51.2 42.5 41.9 39.8
Experiment 2
Week
Cows
NaturalPhotoperiod 18:6D
Heifers
NaturalPhotoperiod 18L:6D
1 44.2 44.9 37.2 40.12 42.1 43.0 38.5 42.2
3 44.4 42.1 35.4 42.0
4 46.5 44.0 39.9 43.6
5 48.7 44.2 39.6 40.7
6 45.8 44.0 36.7 39.7
7 44.6 45.6 40.7 41.8
8 45.7 42.1 40.0 39.4
9 42.9 42.2 37.1 36.5
10 41.3 39.2 39.4 38.5
11 40.8 39.6 35.4 38.5
12 45.8 45.8 40.2 40.8
Appendix Table 2. Accuracy of KaMar Heatmount Detectors in Cows and First Calf Heifers inExperiment 1.
Number ofcows in estruswith KaMaractivated
Number ofKaMar activatedcow not in estrus(False positive)
Number ofcow in estruswithout KaMaractivated
Number of cowsin estrus with KaMaractivated but no visualobservation of heat
Cows 30 17 15 7
First calf heifers 30 37 4 16
64
Appendix Figure 1. Mean kilograms feed consumed (as fed) per dayfor cows exposed to two photoperiods (18L:6Dand 24L:OD).
50
)-
0
El 45
0)ct
ist
3d 24L : OD
0
3 40wIt.
APPENDIX
FIGURE I
CD
35
V
10
0
66
Appendix Figure 2. Mean kilograms feed consumed (as fed) perday for heifers exposed to two photoperiods(18L:6D and natural).
45
>-
0
0o0 40wLA.
rnaow2mcozoo 350wwk.oX
30
;0
7
/c-1o- 0/ \
18L:66-- -- --
APPENDIX
FIGURE 2
NaturalPhotoperlod
I I I 1 i 1 t 1 1 I I2 4 6 8 10 12
WEEKS