j anim sci-1998-brosh-3054-64

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A. Brosh, Y. Aharoni, A. A. Degen, D. Wright and B. Youngunder different conditions

Estimation of energy expenditure from heart rate measurements in cattle maintained

1998, 76:3054-3064.J ANIM SCI

http://jas.fass.org/content/76/12/3054the World Wide Web at:

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HEART RATE AND ENERGY EXPENDITURE IN CATTLE 3055

Table 1. The arrangement of the treatments during the experimenta

aThe letter s repr esent the trea tmen t conditions a ccording to the following order. 1st : diet of low- (L )and high- (H ) energy concentra tion, 2nd: exposure to sun (E ) or protected by shade (P ), and 3rd: feedingi n t h e m or n i n g ( M ) or a f t er n oon ( A ) .

bAcclima tizat ion period.

Animal

Da ys 1 2 3 4 5 6 Ch a n ge of

14b L E A L P A H E A H P A H E A H P A

511 L E A L P A H E A H P A H E A H P A

1218 L E M L P M H E M H P M H E M H P M Tim e fed

1925b L P M L E M H P M H E M H P M H E M Sh a de

2531 L P M L E M H P M H E M H P M H E M3238 L P A L E A H P A H E A H P A H E A Tim e fed

3952b H E M H P M L E M L P M L E M L P M Diet s

5359 H E M H P M L E M L P M L E M L P M

6066 H E A H P A L E A L P A L E A L P A Tim e fed

6773b H P A H E A L P A L E A L P A L E A Sh a de

7479 H P M H E M L P M L E M L P M L E M

8085 H P A H E A L P A L E A L P A L E A Tim e fed

Table 2. App roximate analysis (% dry matter) and ME of the low- (L)and high- (H) energy d iets consumed by the heifers

aCrude fiber.

E t h er ME ,

Diet OM CP ext r a ct CF a NDF MJ /kg

L 89.77 7.68 1.31 52.93 68.53 7.21

H 93.56 16.92 2.23 18.12 29.53 10.63

1979; Richards and Lawrence, 1984; Renecker andHudson, 1985; Yamamoto, 1989). This method could

be most useful because recent developments in microe-

lectr onics a llow th e use of small HR r adio tran smitt ers

t o m e a s u r e H R o f a n i m a l s i n t h e i r n a t u r a l h a b i t a t .

The objective of this study was to determine whether

H R in ca t tle ca n be u sed t o es tim a te E E u n der

different nutritional and environmenta l conditions.

Materials and Methods

Six tr ained 12-mo-old H ereford heifers (345 10.8

k g B W ) w er e i mpl an t ed w it h h ear t -r at e r ad io t r an s -mi t t er s (T elon i cs , M es a, A Z ) ap p r ox imat el y 1 mo

before commencement of m easurements. During t he

85-d st udy, HR for each animal was measured for 5

min every .5 h throughout every day. The six heifers

w er e s t u d i ed i n a 2 2 2 ar r an g emen t ( h i g h - an d

low-energy feed; exposure to and protection from solar

r a d ia t ion ; fe d in m or n in g a n d in a f t er n o on ) a n d

u n d er w en t a ll t r e a t m en t s a s ou t lin e d i n T a ble 1 .

Me as ur em en t s w er e m a de d ur in g t h e s um m er

( J a n u a r yMar ch) of 1993 in southeast Queensland,

Australia, a subtropical region with summer tempera-

tures commonly over 30

C . A n imal s w er e k ept i n -dividually in open feedlot pens, each 40 m 2. Shade was

provided in a bout half the area of each of the pens:galvanized iron sheets, at a height of 2.2 m, covering

11.5 m 2, a n d 7 0 % s h a d e c l o t h , a t a h e i g h t o f 4 m ,

cover in g 1 2 m 2.

The animals were fed either a high-energy diet ( H)

of 80% concentrate and 20% sorghum hay, or a low-

energy diet ( L) of only sorghum hay. The ME of the

concentra te was calculat ed from its composition and

known energy equivalents. The ME of th e sorghum

hay offered a nd left over wa s deter mined by n ylon bag

measurements of organic ma tter digestibility (Seta la,

1983) and assuming a value of 15.06 MJ/kg digestible

or g an ic mat t er (M i n s on , 1 9 8 2 ). T h e ap p r oxi mat e

a n a lys is (AO AC , 1 9 8 0) of t h e fe ed e a t en a n d it scalculated ME, taken as offered minus left over, are

p r es en t e d in T a ble 2 .

The quantity of feed given was regulated to reduce

the refusals to less than 5% of that offered, and it was

give n e it h er in t h e m or n in g ( 08 0 0 t o 0 8 30 ) or

afternoon (1630 to 1700 ). Refusals were collected and

weighed once weekly.

Oxygen uptake was measured by the use of a face

mask open-circuit respirat ory system (Taylor et al.,

1982). The accuracy was checked gravimetrically by

injecting nitrogen into the mask (McLean and Tobin,

1990). The EE was calculated assuming 20.47 kJ/L O2( N i co l an d You n g , 1 9 9 0 ).


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BROSH ET AL.3056

Measurements of HR and O2 u p t ak e w er e mad e at

t h e s a m e t i m e for e a ch a n im a l on e a ch t r e a tm e n t

d u r in g t w o con s ecu t ive d a ys w h en p en n ed . T he

animals stood most of the time and, occasionally, lay

d ow n . M easu r emen t s w er e mad e ov er 1 5 t o 2 0 mi n

each time: between 0700 a nd 0830 before morning

feeding and between 1400 and 1530 in the afternoon.

D at a w er e av er ag ed ever y 5 s , r ecor d ed on a d at a

logger (Mini-Logger

, M in i -M it t er C o., S u n r iv er ,O R ), a n d t r a ns fe rr ed t o a la p top com pu t er for

processing. For analysis, the data were pooled over

30-s intervals. For each such simultaneous measure-

m en t of H R a nd O2 u pt a ke, t he O2 p u ls e w a s

ca lcu la t ed a s t h e O2 u p t a ke p er h e a r t be a t .

T h er e w er e fou r m e a su r em e nt s p er a n im a l p er

t r eat men t an d 3 2 meas u r emen t s p er an i mal i n t o t al ,

composed of two measurements for each time (morn-

ing or afternoon) for each treatment. For analysis of

the stability of O2 pulse, the difference between these

t w o m e a su r em e n ts w a s t e st e d.

O xyge n u pt a ke a n d H R d ur in g e xer cis e w er e

measu red simultan eously on four occasions for eachanimal on each diet. Measurements were made over

20 min on 2 d for each animal, each day, once in the

morning and once in the afternoon. A circular walker

wa s u se d t o e xe rcis e t h e a n im a ls a n d t h e r a t e of

wa lk in g wa s u p t o 6 k m/h .

The EE pulse was calculated as the energy expendi-

t u r e p er h ear t b eat . D ail y an i mal E E w as calcu l at ed

by multiplication of the total daily heart beats by the

a ve r a ge E E p u ls e.

Body weights of the heifers were determined every

2 wk and a t the beginning and end of each t reatment.

Live weight ( LW) a n d d a i ly L W g a in ( LWG) w er e

calculated from the regression slope of all the meas-

u r em en t s of LW on e ach d ie t.

M et eor ol og ical d at a (am b i en t t emp er at u r e [Ta ],

black globe temperature [BG], and relative humidity

[RH] ) w er e col lect ed b et w een 0 70 0 an d 0 83 0 an d

b et w een 1 40 0 an d 1 53 0, an d b lack g lob e h u mi di t y

i n di ces ( BGHI) (B u ffin gt on e t a l., 1 9 81 ) w er e

calculated.

Statistical A nalysis

R eg r es s ion an al ys is w as u s ed t o t es t w h et h er a

relationship existed between O2

u p t a k e a n d H R a n d

between O2 pulse and HR. The regressions were done

separately for the data taken at rest and at exercise.

For exercising an imals, a verages of O2 u p t ak e an d O2pulse for each 5-beats/min interval of HR were taken

for each animal at each state. Regressions were also

done for all the animals, either at rest or exercising,

with a random animal effect, to obtain 1) intercepts

a n d s lop es for e a ch a n im a l i n e a ch s t a t e a n d 2 ) a

common s lop e t h at ch ar act er i zed t h e s t at e. I n t h e

resting animal model, fixed effects were assigned for

ra diation conditions, time of feeding, time of mea sure-

m e n t, a n d d ie t , w it h e it h er a lin e a r or a q ua d r a t ic

effect of HR within diet. In the exercising model, a

fixed effect was assigned to diet, and either a linear or

a q u adr at i c effect w it h i n d iet .

T he e qu a t ion s of t h e m od el w er e a s foll ow s:

Y = A + R + T F + T M + D /H R + e [1]

Y = A + R + TF + T M + D / (H R + H R2) + e[2]

The equations of t he models for exercising were as

follows:

Y = D / H R + e [3]

Y = D / ( H R + H R2) + e [4]

where Y = O2 uptake or O2 pulse, A = random a nimal

effect, R = radiation (exposed or protected) effect, TF

= time of feeding (morning or afternoon) effect, TM =

time of measurement (morning or afternoon) effect, D

= diet (L or H ) effect, H R, HR2 = linear an d quadrat ic

e ffe ct s of h ea r t r a t e, a n d e = e rr or .

The regression equations for each animal, l inear

and quadra tic, based on the exercising data , were used

t o exami n e w h et h er i t s O 2 u p t ak e at r es t cou l d b e

estimated from its HR. The O2 pulse was calculated in

the same way except that only a linear regression was

used. These estimated values were compared with the

observed values, which were recorded simultaneously

wit h t h e H R, by m ea n s of a pa ir ed t-test.

The effect of time elapsed between a last given meal

and measurement on the observed values of HR, O 2

u p t a k e , a n d O2 p u ls e d u r i n g r es t w as es t imat ed b yl in ear r egr es si on of t h es e v ar iab les on t h e elap s ed

time (hours). In this regression, a random effect was

assigned t o the an imal, a nd fixed effects to conditions

of r adiation, time of feeding, time of measurement,

a n d d ie t .

The contr ibution of the var iance between th e pair of

m e a su r e me n t s for e a ch s it u a t ion t o t h e r e sid u a l

v ar i an ce w as t es t ed b y mean s o f t h e r es i d u al er r o r

when all the fixed effects and the linear effect of the

elapsed time were a ccount ed for by the regression. The

absolute value of the difference between the residuals

of the two replicates for each state for each animal (n

= 9 6 ) w a s ca l cu la t e d, a n d t h e m e a n va lu e of t h i s

difference was averaged for each variable and com-

p a re d wit h t h e m ea n va lu e of t h is va r ia ble .

All analyses were made with Genstat 5 Release 3.2

( L aw es Ag r icu l t u r al T r u s t , 1 9 9 5 ).

Results and Discussion

Morning an d a fternoon air temperatur es were 23.5

.8 and 30.2 .7C, whereas RH were 65 2 and 45

3%, respectively. Black globe temperatures were 25.2


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Table 3. Linear r egression of O 2 uptake (mL O2/ (kg.75h)) and of O 2 pulse (mL O2/

(kg .75beat) on heart rate (HR), with fixed effects of rad iation (exposed or

protected), time of feeding (morning or afternoon), time of measurements(morning or afternoon), and diet (L or H ) at rest (df = 82)

and at exercise (df = 102)

aSignificance: NS, not significant .bValue/beat.cDifference of slopes bet ween di et s L a nd H (L H ).P < .10.**P < .01.*** P < .001.

Rest E xer cise

E ffect Va lu e SE Pa Va lu e SE Pa

O2 upt ake

Ra dia t ion 14.7 20.0 NS

Time of feeding 39.2 19.8

Ti me of measurement 65.2 21.0 **

Diet 146 172 NS 145 251 NS

HR sl ope on L di et b 18.1 2.5 *** 23.2 1.7 ***

Difference H dietc 3.7 2.8 NS 3.4 2.5 NS

r2

of r egr ession .933 .742O2 pulse


Time of feeding 8.14 4.33

Ti me of measurement 17.98 4.58 ***

Diet 2.4 37.5 NS 14.3 39.8 NS

HR sl ope on L di et b .34 .55 NS 1.24 .27 ***

Difference H dietc .37 .61 NS .26 .39 NS

r 2 of r egr ession .314 .202

Figure 1. Average d aily h eart rates (SE) of heifers on

high (n = 4; D) and low (n = 2; o ) energy diets. Feed w asgiven at 0830.

.8 and 30.2 .7C u n d er t h e s h ad e an d 3 7 . 6 1.3

an d 4 5. 0 1.7C in t h e s u n in t h e m or nin g a n d

afternoon, respectively. Black globe hum idity indices

were 72.6 1.1 and 80.1 .7 in the shade and 84.9

1.3 and 92.1 1 . 6 i n t h e s u n , i n t h e mo r n i n g an d i n

the afternoon, respectively.

T h e H R w as h i gh er i n h ei fer s f ed t h e H d iet t h an

the L diet and increased in all heifers during and after

fe ed in g (F i g u r e 1 ) .

Previous studies that measured HR to estimate EE

u s ed l in ear or l ogar i t h mic r egr es si on equ at i on s t o

r elat e O2 uptake and HR (Webster, 1967; Yamamoto

et al., 1979; Richards and Lawrence, 1984; Reneckeran d H u d s on , 1 9 85 ; P u r w an t o et al ., 1 9 9 0 ). I n t h i s

study, within each diet, l inear regression equations

b es t d es cr i bed r es t in g an i mals , w h er eas q u ad r at ic

regression equations best described exercising animals

(T a b le s 3 a n d 4 ) . Ge ne ra lly, t h e s lop es of t h e

equations for exercising animals were st eeper than

t h os e of r e st in g on e s (F i gu r e 2 ) .

T he se d a t a i nd ica t e t h a t t h e d ep en d en ce of O2uptake on HR during rest is l inear, and, hence, the O2u p t ak e p er h ear t b eat ( t h e O2 pulse ) does not depend

on HR under these conditions (Figure 3). In contrast

t o t h e r es t in g con d it i on s , a p h ys ical s t r ai n s u ch as

t h at i mpos ed d u r in g exer ci se i n du ced a O2 uptakeincrease that was not linearly related to the increase

in HR. However, if the O2 uptake could be accurately

described by a quadratic regression on HR, then the

O2 pulse should be satisfactorily described by a linear

regression, because the O2 pulse is given by O2 uptake

divid ed by H R. Th e fin din g t h at t h e O2 pulse

regression on HR was not linear suggests, therefore,


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BROSH ET AL.3058

Table 4. Quad ratic regression of O 2 uptake (mL O2(kg.75 h ) an d o f O2 pulse

(mL O2 / (kg.75beat) on heart rate (HR), w ith fixed effects of rad iation

(exposed or protected), time of feeding (morning or afternoon), timeof measurements (morning or afternoon), and diets (L or H)

at rest (df = 82) and at exercise (df = 102)

a Significance: NS, not significant ; P < .10, *P < .05, **P < .01, ***P < .001.bValue/beat.cValue/beat 2.dDi fference of sl opes bet ween di et s L a nd H (L H ).

Rest E xer cise

E ffect Va lu e SE Pa Va lu e SE Pa

O2 upt ake


Time of feeding 44.0 20.6 *

Ti me of measurement 59.6 21.7 **

Diet 286 1,207 NS 2,880 810 ***

HR sl ope on L di etb 21.2 34.6 NS 43.5 7.8 ***

H R2 sl ope on L di et c .387 .339 NS .106 .040 **

Di fference HR H di et 2 24.0 39.0 NS 44.2 14.6 **

Difference H R2 H d ie t2 .33 .35 NS .178 .064 **


O2 pulse


Time of feeding .922 4.48 *

Ti me of measurement 16.66 4.72 ***

Diet

69 262 NS 381 130 **HR sl ope on L di et 9.01 7.51 NS 5.30 1.25 **

H R2 slope on L diet .092 .074 NS .021 .0065 **

Di fference HR H di et d 5.57 8.48 NS 5.12 2.34 *

Difference H R2 H d ie td .075 .077 NS .018 .010


t h a t t h e r egr es sion of O2 u pt a ke on H R d ur in g

exercise could not be described satisfactorily, even

w it h a q u ad r at ic p ol yn omi al.

During exercise, thr ee para meters that contribute

to the O2 upta ke ar e alter ed: 1) HR; 2) A-V difference,

t h e d iffer en ce b et w een ar t er i al an d ven ou s O2 in

b lood ; an d 3 ) s t r ok e v ol u me ( E ck er t et al ., 1 98 8;

Jones et al. , 1989). The negative slope on HR 2 could

have resulted from a reduction in t he rate of increase

of the A-V difference (J ones et al., 1989) and from a

reduction of the stroke volume as the O2 u p t ak e an d

HR increased as a result of exercise. This is probably

why, when a polynomial of the third order was used to

describe the relations of O2 u p t a k e a n d O2 pulse on

HR, neither of t he regressions was improved, com-

pared with t he second-order polynomial (resu lts of thet h i r d-or d er p ol yn omi al ar e n ot p r es en t ed ).

During rest, the effect of time of feeding on the O 2u p t ak e an d t h e O2 pulse tended to be significant, and

the effect of time of measurement on these parameters

was significant. These parameters were lower in the

a ft er n oon t h a n t h e m or n in g fe ed in g a n d in t h e

afternoon than the morning measurement. No effect of

ra diation was detected on either O 2 uptake or O2 pulse

on H R.

Individual regression equations for each animal on

each diet (Figure 2) generated when exercising were

used to estimate EE at rest. The difference between

estimated a nd measured values was significant only

for t h e L d iet , a n d on l y w h en t h e l in ear r egr es si on

equ at i on s w er e u s ed ( T ab l e 5 ) . H ow ever , t h e s t an -

d ar d er r o r s of t h e mean w er e mu ch l ow er w h en O2p u ls e w a s u s e d t h a n O2 u p t a ke for t h e lin e a r a n d

q u ad r at ic r egr es si on s . A s can b e s een i n F i gu r e 2 ,

regression equa tions differed am ong an imals a nd were

affect ed b y d iet ar y M E . T h er efor e, t o es t imat e E E

from HR, a regression equation should be determined

for each animal when it consumes a diet similar to the

one in which the animals E E is to be estimated. In

contrast to this, despite the significant effect of dietary

ME on O2 p u ls e, t h e r a n ge of va r ia t ion s a m on g

animals and diets is minor (Figur e 3 ), so O2 pulse (or

E E p u l s e) t o es t i mat e E E b y H R i s l es s af f ect ed b ydiet than was EE estimated by regression equations.

T he H R in cr e a se d a ft e r t h e m e a l a n d d ecr e a se d

t h er eaft er ( F i gu r e 1 ) . T h e cor r elat i on of O 2 u p t ak e

a n d O2 pulse with HR (Tables 3 and 4) was affected

by th e time of feeding, morning or afternoon, and by

t h e t i me of meas u r emen t , an d i t w as p os t u lat ed t h at

these effects could also be at tributed to the time t hat

e la p se d b et w ee n t h e m e a l a n d t h e m e a su r e me n t .

Therefore, we tested the effect of elapsed time on HR,

O2 u p t ak e, an d O2 pulse (Table 6). We used all 192

in divid ua l m ea s ur em en t s of H R a n d O2 uptake,


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Figure 2. Oxygen uptake (mL/ (kg .75h) SE on the ordinate and heart rate (beats/ min) on the abscissa of six

heifers on low- (L) and h igh- (H) ME d iets. Measurements at rest in the pens (R, empty symbols) und er all treatments

and at exercise using a walker (W, filled symbols). Linear regression, broken line for resting animals and quadratic

regression, full line when exercising. Note the different axes limits for each animal.

comprising t wo measur ements for each combination of

d ie t , t im e of fe ed in g, t im e of m e a su r e me n t , a n d

radiation conditions for each heifer. Random effect of

the animal and fixed effects of all the above-mentioned

con d it i on s w er e accou n t ed for b y t h e r egr es si on

equations obtained in the first step, in addition to the

lin ea r e ffe ct , t h e e la p se d t im e. I n e ach of t h e

regressions of HR, O2 u p t a ke , a n d O2 p u l s e, al l t h e

fixed effects that were not significant in the first step

were excluded from t he regression in t he next step.

Thus, only diet and time of measurement effects were

included in the regression of HR, only diet effect in the

regression of O2 uptake, and all the fixed effects but

radiation in the regression of O2 p u ls e o n t h e t i me

elapsed since the last meal before the measurement.

T h e H R a n d O2 uptake decreased with increasing

time, at rates of .72 and .92% of the mean per hour,

respectively, which left the O2 pulse relatively cons-


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BROSH ET AL.3060

Figure 3. Oxygen pulse (mL/ (beatkg.75) SE and heart rate (beats/ min) of six heifers on low- (L) and on high- (H)

ME diets at rest in the pens, panels A and B, respectively, and at exercise using a walker on diet L and on diet H,

panels C and D, respectively. Note the different axes limits for each panel.

Table 5. The percentage difference between m easured O2 u p t ak e an d O2 pulse ofheifers at rest and those estimated from linear and quadratic regression

equations at exercise. The regressions for exercising animalswere calculated separately for each one (n = 6)

a NS, not si gni fi cant ; *P < .05.

Low-en er gy diet H igh -en er gy diet

P ar am et er Ca lcu la tion % differ en ce SE Pa % differ en ce SE P

O2 u pt a ke Linea r 25.5 9.8 * 1.0 6.2 NS

O2 u pt a ke Qu a dr a t ic 3.3 13.4 NS .6 7.0 NS

O2 pu lse Aver a ge .6 2.5 NS 1.0 4.0 NS

t an t w it h t i me. E v en t h ou g h t h e effect of d i et w as

highly significant for all three parameters, the magni-

tude of this effect was only 10.5% of the mean for the

O2 pulse, compared with 68.5 and 59.0% of the mean

for H R a nd O2 upta ke, respectively.

Th e O2 p u ls e w as r elat i vely con s t an t for each

an i mal, comp ar ed w it h O2 u p t ak e, for t h e r an g e o f

conditions in the pens, provided that the animals were

n ot u n de r in t en s ive p h ys ica l s t r a in . We s u gge st ,

t h e r efor e , t h a t O2 p u ls e is t h e m os t a p pr op r ia t e

p a r a m et e r t o u s e in e st im a t in g E E fr om t h e H R of

an i mals i n r es t con d it i on s . I n p en s , t h e p er cen t age

ch an g e b et ween d ail y mi n imu m an d max imu m H R

was 80 to 175% on the L diet and 70 to 149% on the H

d iet , w i t h con s t an t O2 p u ls e t h r ou g h ou t t h i s r an g e

(T a b le 3 ) .

D et er min at i on s of H R , O2 u p t a ke , a n d O2 pulse

were done twice for each animal on two separate days,


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Table 6. The linear effect of time elapsed (h) from the previous feeding timea

to measurement, and fixed effects of treatments in the pens,o n H R , O2 uptake, and O2 pulse (n = 192)

aVaried bet ween 3.4 an d 30.2 h .bUnits/h. Evaluated in a common analysis of fixed and linear effects. Only significant fixed effects were

included.cBeats/min.dNS, n ot significant ; *P < .05, ***P < .001.em L O2/kg

.75.fmL O2 /(kg

.75 beat ).gDash indicates that the fixed effect did not account for a significant amount of variance in an initial

m o d e l a n d t h u s w a s d r o p p e d f r o m t h e a n a l y s i s u s e d t o g e n e r a t e t h e d a t a i n t h i s t a b l e .

Fixed effects

Tim e of Tim e of Tim e fr om

Depen den t pa r a m et er m ea su r em en t feedin g Diet m ea l, h b

H Rc

Slope 4.41 48.2 .508

% of m ea n 6.3 68.5 .72

SE 1.29 1.16 .091

Pd *** *** ***

O2 upt akee

Slope g 613.2 9.54

% of Mea n 59.0 .92

SE .34 .024

Pd *** ***

O2 pulsef

Slope 17.81 8.48 26.39 .183

% of Mea n 7.1 3.4 10.5 .07

SE 3.67 3.43 3.26 .269

Pd *** * *** NS

Table 7. The O2 pulse (mL/ (kg.75beat) and CV (SE/ mean100) of cattle at rest und er different conditions

aAverage of si x measurement s of 16 ani mal s.bM ea s u r e m e n t s o f a n i m a ls a t r e s t .

An im a ls a n d con dit ion s n BW, kg O2 pu lse CV, % Refer en ces

H eifer s, low-en er gy diet 6 345 265 2.60 P r esen t st u dy

H eifer s, h igh -en er gy diet 6 337 238 2.50 P r esen t st u dy

St a n din g H in t er wa eelder oxen 7 494 347 2.8 Rom et sch et a l., 1997

St a n din g Zebu oxen 5 516 300 2.7 Rom et sch et a l., 1997

Swedish Red a n d Wh it e st eer s 3 449 377 J on es et a l., 1989

Sim m en t a l oxen 562 338 Cla r , 1991

Bor a n cows 475 429 Zer bin i et a l., 1992

H eifer s of va r iou s br eeds 8 123177 252 6.80 Lia n g et a l., 1997

Black-Pi ed da i ry cat t l e bul ls (16 a ) 6 280350 286 2.4 Der n o et a l., 1997

Mean SE of t h e 9 r efer en ces 315 3.2 315 3.2 1.0 CV of t h e 9 r efer en ces

under each set of conditions in t he pens. The mean

absolute values of the differences between the residu-

als of the two replicates for each state for each animal

were .52 beat/min, .78 mL O2/(kg.75

h), a nd .90 mL O2/(k g .75 b ea t ) for H R, O2 u pt ake, a nd O2 pulse,

respectively. These differences were equal to only .74,

3.90, an d .36% of the mean values of HR, O 2 uptake,

a n d O2 pulse, respectively. It is suggested, therefore,

t h at a s in g le d et er mi n at ion i s s u ffi ci en t .

T h e O2 p u ls e of a n u mb er of cat t l e b r eeds u n d er

different conditions at rest is presented in Table 7.

The variance in each breed was small. It is suggested,

therefore, th at despite th e individual chara cter of the

O2 pulse and its dependence on diet and environmen-

tal conditions, HR can provide an estimation of theirE E . M or eover , p r ov id ed t h at t h e cat t l e i n p en s a n d

p a st u r e a r e n ot e xp os ed t o e xe r cis e, d a y-t o-d a y

ch a n ge s i n H R p r ovid e a r e lia b le e st im a t ion of

ch a n ge s i n E E .

It can be concluded th at the E E of the heifers can be

es t imat ed fr om H R meas u r emen t s , u s i n g q u adr at i c

equ at i on s t h at r elat e O2 u p t ak e t o H R o r b y u s i n g a


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BROSH ET AL.3062

Figure 4. Metabolizable energy intake (A), energy

expenditure (B), and retained energy (C) of six heifers.

Four were fed a high-energy diet (10.62 MJ/ kg DM of

ME) during the first 45 d (thin lines) and a low-energy

diet (7.21 MJ/ kg DM of ME) subsequently. The other

two (thick lines) were fed the low- and then high-energy

diets.

consta nt value of O2 uptake per heartbeat (O 2 pulse),

which is less affected by t he nutr itional conditions.

The relation of O2 uptake to HR is dependent on the

cau s es f or ch an g es of H R r at h er t h an on H R i t self.

Use of HR to estimate energy retention and energy

b al an ce w as ev al u at ed . T h e M E i n t ak e ( MEI) , E E ,

an d r et ai n ed en er g y ( RE) of t h e h eifer s d u r i n g t h e

en t ir e s t u d y ar e p r esen t ed i n F i gu r e 4 A, B , a n d C ,

respectively. The LW, gain, and the energy balance

param eters on each diet during the entire experiment

are presented in Table 8. The MEI of the heifers was

directly related to the ME concentration of the diet,

an d t h e E E an d t h e R E f o l l o w ed t h e ch an g es i n t h e

MEI. Before the start of the experiment, the heifers

w er e fe d t h e L d ie t ; d u r in g t h e fir s t d a ys of t h e

exp er i men t , t h e i n t ak e o f t h e h eifer s on t h e H d iet

greatly increased, resulting in similar increases in the

EE and RE. Because the amount of feed given duringeach period was constant and the weight gain of the

an i mals on t h e H d iet w as p os it i ve, t h e i n t ak e p er

meta bolic weight decreased during each per iod. When

the diets were switched, th e MEI followed th e chan ges

in the diet energy density and, consequently, so did

t he E E a nd t he RE .

Calculation of EE by mu ltiplication of th e HR by

the EE pulse, calculated from the O2 pulse, was less

accurate immediately after the change in feed quality.

For calculation of EE during that period, the EE pulse

of t h e p r evi ou s d iet w as u s ed for t h e cal cu l at ion .

Because the difference between the EE pulses on the

two diets was only 10.5% and the time taken for the

h ei f er s t o r each s t ab i l i t y i n i n t ak e an d E E af t er t h e

switch of diets was short, the resulting inaccuracy in

t h e d et e r m in a t ion of E E w a s s m a ll.

Predicted EE according to the National Research

Council (NRC, 1984) is 432 4 7 an d 7 5 0 4 6 k J /

(dkg .75 ) on t h e L a n d H d ie ts , r e s pe ct ive ly (t h e

i n di vi du al M E I an d t h e L WG of t h e h eifer s i n t h e

present study were used for t he calculat ion). The NRC

predictions were not significant ly different from our

e st im a t ion a ccor d in g t o t h e H R a n d t h e E E p u ls e

(T a b le 8 ) .

The calculated RE per LWG for the H diet (28.4 1 . 5 M J / k g L W G ) t en d ed t o b e l ar g er t h an t h e v al u e

obtained by use of the observed LW and LWG in the

NRC (1984) equation (23.6 1.0 MJ/kg LWG). The

LWG on t he L diet wa s negligible, as wa s t he RE, a nd,

ther efore, th e calculation of RE per LWG from t hese

va lu e s w er e n ot d on e.

We conclude t hat HR, a relatively easy measure-

ment, can be u seful and accurat e in estimating EE. To

increase the accuracy of the estimation of EE by HR,

the relationship of HR to EE should be established for

each individual animal. In addition, t he nutr itional

regimen used in establishing the relationship should

be similar to that for the animal in which EE will be

estimated. Measurements obtained using this method,

combined with MEI, would allow estimations of body

en er g y ch an ges i n an i mals l os in g or g ain i n g b od y

weight.

Implications

H ear t r at e i s r el at i v el y eas y t o meas u r e, an d t h i s

meas u r emen t s eems t o b e a p r act i cab le met h od for

estimating accurat ely t he short-term and long-term


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Table 8. Body weight, live w eight (LW) gain (LWG), energy balance parameters,and energy content in LW gain of the heifers (mean of six heifers SE) that

were fed high- (H) and low- (L) energy d iets. The animalswere kept in individual pens during the summer

akg .bg/d.cg/(dkg.75 ).dMet abol izable energy i nt ake, kJ / (dkg.75) .eEnergy expendi t ure, kJ/ (dkg .75) .fRet ai ned energy, kJ / (dkg.75) .gNE g, energy cont ent i n l ive wei ght gai n, kJ/ g.hNot calculated because of the negligible LWG.iPeriod of adaptation to the diets and period of diet changeover in the middle of the experiment (about

2 wk for each per i od) ar e i ncluded.

Diet BWa Gain b LWG c ME Id E E e RE f N E gg

H 337 1,460 18.45 1,190 670 520 28.4

SE 15 120 .88 25 10 22 1.5

CV 4.6 8.0 .8 2.1 1.4 4.14 5.20L 345 157 2.079 468 394 74 h

SE 10 97 1.233 26 19 11

CV 3.0 61.9 59.3 5.6 4.8 14.6

Alli 337 810 10.37 843 541 301 29.6

SE 13 50 .64 13 8 9 2.1

CV 6.2 6.3 6.2 1.6 1.4 3.0 7.2

variations of energy expenditure in free-range cattle.

When metabolizable energy intake is also measured,

energy retention in a nimals and the energy content of

the gain or loss of body weight can be estimated. This

w ou l d al low t h e d et er min at i on s of en er g y r equ i r e-

men t s o f an i mal s an d w o u l d b e mo r e accu r at e t h an

s imp ly u s in g ch an g es i n b od y m as s as a cr i t er i on .

Under certain circumstan ces, i t would also allow the

calculation of the efficiency of u tilizat ion of energyi nt a k e for m a in t e na n ce a n d for gr ow t h .

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