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J. D. Pagan and H. F. HintzSubmaximal Exercise

Equine Energetics. II. Energy Expenditure in Horses During

1986, 63:822-830.J ANIM SCI

http://www.journalofanimalscience.org/content/63/3/822services, is located on the World Wide Web at:

The online version of this article, along with updated information and

www.asas.org

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E Q U I N E E N E R G E T I C S . I I . E N E R G Y E X P E N D I T U R E I N H O R S E SD U R I N G S U B M A X I M A L E X E R C I S E

J. D. Pagan a and H. F. Hintz2'3Cornell University, Ithaca, NY 14853

A B S T R A C TEnergy expenditure was measured in four geldings (433 to 520 kg) during submaximal exerciseon a racetrack using a mobile open-circuit indirect respiration calorimeter. A total of 304 5-minmeasurements of O 2 consumed and CO 2 produced were taken. Measurements were made with andwithout riders. The amount of energy expended by the horses was exponentially related to speedand was proportional to the body weight of the riderless horse or the combined weight of the horseplus rider and tack. Total energy expended by the four hones walking, trotting, cantering was bestdescribed by the equation:

Y = e 3.02+-0065Xwhere Y = energy expended (cal.kg'l.min t) and X = speed (m/min). Digestible energy (DE)required above maintenance was calculated as

DE (kcal.kg-t .h -t) -- e3"~ -- 13.92 X .06..57

(Key Words: Energy, Horses, Exercise, Oxygen.)

I n t r o d u c t i o nThe main productive function in horses is

work. This work may vary from high speedracing at speeds over 1,150 m/m in to enduran cerides, where horses may travel 167 km at a ratenear 250 m/min, to draft work where horsespull or carry heavy loads at slow speeds. In allthese types of work, energy is the dietary factormost likely influenced by exercise.

The National Research Council estimatedenergy requirements for various activities(NRC, 1978), but these estimates were basedon limit ed data. The following studies wereconducted to measure energy expenditureduring submaximal exercise (walking, trottingand cantering) in horses. Feeding standardswere developed from these data.

1Present address: Manna Pro Corp., 4929 WilshireBlvd., Los Angeles, CA 90036.2The authors gratefully acknowledge the assistanceof Terry Kinsman, Bill Tutton, Lisa Lee , PamelaLivesay-Wilkens,L. V. Sodetholm and Janice Williams.~Send reprint requests to H. F. Hintz, Cornell Uni-versity, Ithaca, NY 14853.Re c e i v e d August 16, 1985.Accepted April 8, 1986.

M a t e r ia l s a n d M e t h o d sThe energy expenditure of horses during

submaximal exercise was measured using amobile open-circuit indirect respiration calo-rimeter (figure 1). The calorimetry system wasvalidated using a nitrogen dilution techniquesimilar to the type used by Fedak et al. (1981).The system was found to measure oxygen con-sump tion with an error of less than 2.0%.

A total of 304 5-min measurements weremade on four geldings (Quarter Horse weighing433 kg; grade horse, 490 kg; Appaloosa, 506kg; Thoroughbred, 520 kg). Each horse'soxygen consumption and carbon dioxide pro-duction was measured at rest and over a rangeof speeds varying from 40 m/m in to 390 m/mi non an 80 0-m oval track w ith a stone- dust sur-face. Step frequency was measured at eachspeed and was used to calculate stride length.Measurements were made on the horses bothwith and without rider. The weight of the riderplus tack averaged 59 kg.During a measurement of 02 cons umpti onand CO2 production, the expired gas from thehorse was collected using the face-mask shownin figure 2. This mask was held on the horse'shead with a leather strap with velero fasteners.An airtight seal was formed between the mask

822 J. Anim. Sci. 1986 .63:822-830

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EQUINE ENERGETICS--EXERCISE 82 3

H081~- - I~ FNO~M A S K

s a m p l e f o ra n a l y s i s

Figure 1. Calor imeter used to measure energy expenditure during exercise .

" 4 ( O U T E I O E A I R4 . . . . . . E X P I R E D G A E

Figure 2. Face-mask used to collect gases duringexercise.

and the horse's muzzle with inflated bloodpressure cuffs. The mask contained two one-way intake valves (V1 and V2) and one one-way outlet valve (V3). Outside air was drawnthrough the mask with a vacuum pump (figure1) and all expired gases were directed through a10-cm diameter flexible hose into the calorime-ter, as indicated by the arrows in figures 1 and2. A continuous aliquot of the gas passingthrough the calorimeter was collected andstored for analysis of oxygen and carbondioxide concentration. The total volume of gaspassing through the calorimeter also was mea-sured, along with its temperature and relativehumidity. The gas volume was adjusted tostandard temperature and pressure of dry gas,and multiplied by the change in composition ofthe collected gas from that of inspired (outside)air to obtain the amount of oxygen consumedand carbon dioxide produced during a measure-

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8 2 4 P A G A N A N D H I N T Z

m e n t . E n e r g y e x p e n d e d w a s c a l c u l a t e d b ym u l t i p l y i n g t h e n u m b e r o f li te r s o f o x y g e n c o n -s u m e d d u r i n g a m e a s u r e m e n t b y t h e o x y g e n ' st h e r m a l e q u i v a l e n t ( k c a l / l it e r ) a t t h e r e s p i r a t o r yq u o t i e n t ( R Q ) c a l cu l a t ed f o r ea c h m e a s u r e m e n t( B r o d y , 1 9 4 5 ) .

T h e c a l o r i m e t e r w a s c a rr i e d o n a w a g o np u l l e d b y a t r a c to r . E l e c t r i c i ty t o p o w e r t h ep u m p s a n d c l o c k o n t h e c a l o r i m e t e r w a s s u p-p l i e d b y a p o r t a b l e g a s o l i n e g e n e r a t o r , a l s oc a r ri e d o n t h e w a g o n . T h e h o r s e b e i n g m e a -s u r e d w a l k e d o r r a n a l o n g s id e t h e w a g o n a n dw a s a t t a c h e d t o t h e c a l o r i m e t e r b y a p l a s ti cf l e x i b l e h o s e c o n n e c t e d t o t h e fa c e -m a s k . T h eh o s e w a s 2 .4 m l o n g a n d 1 0 c m i n d i a m e t e r .D u r i n g e a c h t r i a l t h e h o r s e w e a r i n g t h e fa c e -m a s k w a s l e d b y a r id e r o n a n o t h e r h o r s e t oe n s u r e t h a t i t m a i n t a i n e d a c o n s t a n t s p e e d. T h i sw a s t h e c a s e e v e n w h e n a r i d e r w a s o n t h e h o r s eb e i n g m e a s u r e d b e c a u s e t h e f a c e -m a s k p r e -c l u d e d t h e u s e o f b i t a n d b r i d l e. T h e h o r s e a n dw a g o n w e r e b r o u g h t t o t h e s p e e d a t w h i c h t h em e a s u r e m e n t w a s t o b e t a k e n in a p a r t i c u l a rt r ia l a b o u t 1 m i n b e f o r e t h e 5 - m i n m e a s u r e -m e n t p e r i o d b e g a n . T o t a l d i s t a n c e t r a v e l e dd u r i n g t h e 5 m i n w a s m e a s u r e d w i t h a n e l e c -t r o n i c b i c y c l e o d o m e t e r , a n d t h i s d i s t an c e w a su s e d t o c a l c u l a te sp e e d . S t e p f r e q u e n c y w a sr e c o r d e d b y a n o b s e r v e r w i t h a h a n d h e l dc o u n t e r .

R e s u l t s a n d D i s c u s s i o n

E n e r g y e x p e n d i t u r e s o f th e h o r s e s w i t h a n dw i t h o u t r i d e r s a r e s h o w n i n f i g u r e s 3 t o 1 0 . T h er e l a t i o n s h i p b e t w e e n e n e r g y e x p e n d i t u r e a n ds p e e d w a s b e s t d e s c r i b e d a s a n e x p o n e n t i a lf u n c t i o n . T h e d a t a w e r e tr a n s f o r m e d b y t a k i n gt h e n a t u r a l l o g (I n ) o f e n e r g y e x p e n d i t u r er e g r e s s e d a g a i n s t s p e e d . L i n e a r r e g r e s s i o n s o ft h e d a t a f r o m e a c h h o r s e w i t h a n d w i t h o u t ar i d e r a r e s h o w n i n t a b l e 1 , a l o n g w i t h t h ee x p o n e n t i a l e q u a t i o n s .

M o r e e n e r g y w a s e x p e n d e d b y e a c h h o r s ew h e n c a r r y in g a r i d e r t h a n w h e n u n w e i g h t e d .T h e a m o u n t o f e n e rg y e x p e n d e d b y t h e h o rs e sw a s r e l a t e d t o s p e e d a n d a l s o a p p e a r e d t o b ep r o p o r t i o n a l t o t h e b o d y w e i g h t o f t h e r id e r le s sh o r s e o r t h e c o m b i n e d w e i g h t o f t h e h o r s e p l u st h e r i d e r . I n o t h e r w o r d s , a 4 5 0 - k g h o r s e c a r r y -i n g a 5 0 -k g r id e r w o u l d e x p e n d a b o u t t h e sa m ea m o u n t o f e n e r g y a s a 5 0 0 - k g h o r s e c a r ry i n g n ow e i g h t .

T a y l o r e t a l . ( 1 9 8 0 ) m e a s u r e d t h e e n e r g e t i cc o s t o f c a r r y i n g l o a d s in r at s , d o g s , h u m a n s a n dh o r s e s. T h e l o a d s r a n g e d b e t w e e n 7 a n d 2 7 % o f

a

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0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0

S p e e d ( m e t e r s l m l n )Figure 3 . R e la t ionship be tween energy expende dand speed in a 433-kg Quar te r Horse wi th no r ide r .Tr iangles indica te on e va lue , numbers ind ica te numberof ident ica l va lues .

b o d y m a s s. T h e y a ls o f o u n d t h a t o x y g e n c o n -s u m p t i o n i n c r e as e d in d i r e c t p r o p o r t i o n t o m a s ss u p p o r t e d b y t h e m u s c l e s .

A h o r s e s u s t a i n i n g a l o a d a t r e s t i n c r e a s e d it se n e r g y e x p e n d i t u r e o v e r r e s ti n g w i t h o u t a l o a dt o a d e g r e e p r o p o r t i o n a l t o t h e w e i g h t o f t h ea d d e d l o a d ( A r m s b y , 1 9 0 8 ). W h i l e t r av e l i n g a t

1 0 0 -

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I t I I J I7 0 1 4 0 2 1 0 2 8 0 3 5 0 4 2 0

S p e e d ( m e t e r s / r a in )Figure 4 . Re la t ionship be tween energy expendedand speed in a 433-kg Quar te r Horse ca r ry ing a 59-kgrider . Triangles indicate one value, numbers indicatenumb er of iden t ica l va lues.

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EQUINE ENERGETICS-EXERCISE 82 5

90 m/min, a load of 127 kg caused about an 8%i n cr e as e i n t h e a m o u n t o f e n e r g y e x p e n d e d ( p e rk g o f t o t a l m a s s ).B e c a u s e t h e e n e r g y e x p e n d e d w a s p r o p o r -

t i o n a l t o t h e b o d y w e i g h t o f t h e r id e rl es s h o r s e ,o r c o m b i n e d w e i g h t o f t h e h o r s e p l u s r i d e r , a l ldata could be combined. Linear and exponen-tial e q u a t i o n s f o r t h e c o m b i n e d d a t a ( f i g u r e 1 1 )are shown in table 1.

Stride length was highly correlated (P

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826 P AGAN AND HINTZo f s u b s tr a te t o s u p p ly e n e r g y f o r l o c o m o t i o na n d t h e m a i n te n a n c e o f b o d y f u n c ti o n s . T h ea m o u n t o f n e t e n e rg y e x p e n d e d b y t h e an i m a lf o r l o c o m o t i o n a l o n e c a n b e c a l c u l a te d b y s u b -t r a ct i n g t h e a m o u n t o f e n e r g y e x p e n d e d b y t h ea n i m a l w h i l e s t a n d i n g a t r e s t. A 5 0 0 - k g h o r s ew o u l d b e e x p e c t e d t o e x p e n d 1 3 . 92 c a l ' k g - 1 .m i n - 1 w h i l e s t a n d i n g w i t h m i n i m a l m o v e m e n t

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99 y : e 2 . 3 0 ~ . 0 0 6 4 X

i i i J t t0 9 0 1 8 0 2 7 O 3 6 O 4 5 O

S p e e d ( m e t e r s I m l )Figure 9. Relationship between energy expendeda n d speed in a 520-kg Thoroughbred with no rider.Triangles indicate one value, numbers indicate numberof identical values.

8 0cEov 6 5

CLXUJ

~ 3 6oc

u i

2 0

5 2 0 ~ k g T h o r o u g h b r e d 9

( w i t h r i d e r )

y : e 2 - 6 6 + . 0 0 6 0 X

i i i i t i

S p e e d ( m e t e r s l m l n )Figure 10. Relationship between en ergy expendedmad speed in a 520-kg Thoroug hbred carrying a 59-kgrider. T riangles indicate on e value , num bers indicatenum ber o f identical values.

i n z e r o e n e r g y b a l a n c e ( P a g a n a n d H i n t z , 1 9 8 5 ) .T o t a l e n e r g y e x p e n d e d b y t h e f o u r h o rs e s

w a l k in g , t r o t t i n g a n d c a n t e r i n g o n t h e r a c e t r a c kw a s b e s t d e s c r ib e d b y t h e e q u a t i o n :

Y = e 3.02+.0065Xw h e r e Y = e n er g y e x p e n d ed ( c a l ' k g - l ' m i n - 1 )a n d X = sp e e d ( m / m i n ) . T h e a m o u n t o f n e te n e r g y ( c a l ' k g - l " m i n - 1 ) e x p e n d e d a b o v e m a in -t e n a n c e a t e a c h s p e e d c a n b e c a l c u l a t e d a s

(e3.02 +.0065x ) _ 13 .92 .T h e e f f i c i e n c y o f u t i l iz a t i o n o f d i g e s ti b l e

e n e r g y ( D E ) b y t h e h o r se f o r w o r k m u s t b ek n o w n b e f o r e D E r e q u i r e m e n t s c a n b e ca l cu -l a te d . A s s u m i n g t h a t b o d y f a t is t h e p r i m a r ys u b s t r a te f o r e n e r g y g e n e r a ti o n i n h o rs e s d u r i n gl o w i n t e n s i t y w o r k , t h e n t h e e f f i c ie n c i e s o fu t i li z a ti o n o f D E f o r f a t p r o d u c t i o n c a n b eu s e d . R e s p i r a t o r y q u o t i e n t s m e a s u r e d in th i se x p e r i m e n t i n d i c a t e d t h a t f a t w a s t h e m a j o rs u b s t r a te f o r e n e r g y g e n e r a t i o n .

T h e e f f i c ie n c y o f u t i li z a t io n o f D E f o r g a in( f a t t e n i n g ) i n h o r s e s w a s e s t i m a t e d t o b e 5 5 %i n h o r s e s f e d a 7 5 % a l f a lf a m e a l - 2 5 % o a t d i e t( P a g an a n d H i n t z , 1 9 8 6 ) . H o f f m a n e t al. ( 1 9 6 7 )r e p o r t e d a n e f f i c i e n c y o f 5 9 % f o r f a t p r o d u c -t i o n i n h o r s e s f r o m D E i n d i e t s c o n s i s ti n g o f6 0 % m e a d o w h a y , 2 0 % o a ts , 1 0% w h e a t b r a na n d 1 0% f l a x s e e d m e a l . I t t h e r e f o r e a p p e a r st h a t a v a l u e o f 5 7 % m i g h t b e r e as o n a b l e f o r t h ee f f i c ie n c y o f u t il i z at i o n o f D E f o r s u b m a x i m a lw o r k . T h i s e f f ic i e n c y v a l u e w i ll d e p e n d o n t h et y p e o f d i e t f e d , a n d w i ll t e n d t o b e l o w e r o nh i g h r o u g h a g e d i e t s a n d h i g h e r i n d i e t s c o n t a i n -i n g h i g h l e v e l s o f c o n c e n t r a t e o r f a t ( B l a x t e r ,1 9 6 2 ; K a n e e t a l . , 1 9 7 9 ) .

D i g e st ib l e e n e r g y ( c a l , k g - 1 . m i n - 1 ) r e q u i r e da b o v e m a i n t e n a n c e c a n b e c a lc u l a te d a se 3"02+'0065X - 13 .92

.5 7T o e x p r e ss t h i s i n t h e u n i ts o f k c a l ' k g - l " h - 1 ,t h i s e q u a t i o n i s m u l t i p l i e d b y . 0 6 . C a l c u l a t i o n su s i n g th i s e q u a t i o n a t v a r i o u s s p e e d s a r e s h o w ni n t a b l e 3 .

A n e x a m p l e o f h o w t h i s e q u a t i o n c o m b i n e dw i t h t h e m a i n t e n a n c e D E e q u a t i o n [ D E ( k c a l /d ) = 1 , 3 7 5 + 3 0 . 0 ( W ) ] p r o p o s e d b y P a g an a n dH i n t z ( 1 9 8 6 ) c a n b e u s e d t o c a l c u l a t e e n e r g yr e q u i r e m e n t s f o r e x e r ci s e is as f o l l o w s : A4 5 0 - k g h o r s e is ri d d e n a t a m e d i u m t r o t ( 2 5 0

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E Q U I N E E N E R G E T I C S - - E X E R C I S E 8 2 7

Z