M E T H O D S FOR M E A S U R I N G P H Y S I C A L C O N D I T I O N A N D E N E R G Y E X P E N D I T U R E IN H O R S E S
University o f Illinois, Urbana 61801
SUMMARY Methods for determining oxygen consumption and carbon dioxide production (respiratory quotient), heart rates and heart recovery rates, and muscle lactic acid production adapted from human studies were evaluated for measurement of energy expenditure and physical condition in horses. Standard metabolic rate (SMR) and energy use of two weanling ponies were determined by indirect calorimetry in a metabolism chamber to test the adequacy of the apparatus to be used on exercising animals. Ponies of 55 and 68 kg had calculated SMR's of 60.49 and 71.06 Kcal/hr, compared to measured values of 63.51 and 72.28 kcal/hr, respectively. Chamber values for oxygen consumption ranged from 11.54 to 33.30 liter/hr and R Q values were within an acceptable range, from .77 to 1.77. 02 consumption values obtained on exercising animals with a specially designed face mask ranged from 50.76 liter/min before exercise to 401.40 liter/rain after a 1/2 hr trot, with R Q range from .55 to 1.56. Resting heart rate tended to decrease and recovery rate to increase through training. Muscle lactic acid concentration increased from approximately 5 /ag/g of muscle at rest to 9.12, 10.86 and 16.51 /~g/g for 1/2 hr, 1 hr, and 1 1/4 hr bouts of walking, respectively. Lactic acid concentration after 1/4 hr and 1/2 hr bouts of trotting decreased t o . 30 a n d . 50 #gig. (Key Words: Horse, Energy Expenditure, Recovery Rate.)
equine athletes with maximum utilization of feed energy. Also, there is a need to determine the energy costs for more specifically defined activities than the customary categories of light, medium, and heavy work. Work in humans by Henry (1950) and Doroschuk et al. (1963) demonstrated the superiority of physiological parameters over p e r f o r m a n c e parameters in measuring improved physical condition due to training. Since the early works of Zuntz (from Armsby, 1903), Hall and Brody (1934) and Brody and Trowbridge (1937), there has been little work done on horses in these areas. The most recent and most significant body of research on physical conditioning and energy cost in exercise has been done on human athletes (Cureton et aL, 1948; Michael and Cureton, 1953; Margaria et al., 1963). This study was designed to evaluate certain physiological parameters adapted from studies on human athletes for use in measuring physical fitness and energy expenditure in horses. Oxygen consumption and respiratory quotient were used to calculate caloric expenditure. Heart rates, heart recovery times, and heart recovery rates were used as indicators of physical condition. Muscle lactic acid concentration was used to determine the metabolic state of the muscles as a possible indication of oxygen debt.
EXPERIMENTAL PROCEDURES
Phase 1 of this study was intended to obtain precise measures of standard metabolic rate, respiratory quotient, and energy use of a INTRODUCTION standing-fed subject. Two 5-month-old ponies Methods for determining physical condition weighing 54.88 kg and 63.08 kg were placed individually into a closed chamber with air tight and energy expenditure in horses are important, plexiglass sides and closely monitored temperasince optimal performance is desired from our ture and humidity (figure 1). Oxygen consumption and carbon dioxide production of the ponies were measured by running two standard 1Current address: 106 Stock Pavilion, Urbana, IL gases, outside air, room air and chamber air 61801. 2Current address: 104 Stock Pavilion, Urbana, IL through Beckman paramagnetic oxygen and 61801. infrared carbon dioxide analyzers. Respiratory 1666 JOURNAL OF ANIMAL SCIENCE, Vol. 46, No. 6, 1978
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D. J. Burke 1 and W. W. Albert 2
MEASURING CONDITION AND ENERGY COST IN HORSES
quotients and energy expenditures were calculated f r o m the following formulas: Respiratory Q u o t i e n t = liters of carbon dioxide p r o d u c e d / liters of o x y g e n consumed: Energy e x p e n d e d (kcal) = 3.866 (liters 02 c o n s u m e d ) + 1.200 (liters CO2 p r o d u c e d ) / - 1 . 4 3 1 (grams N excreted in urine); (Brouwer, 1965). Urinary nitrogen excretion was estimated from data of G. L. Heusner (unpublished data). The ponies were allowed 3 days to acclimate to the chamber, and the trials were run randomly. The standard metabolic rate was d e t e r m i n e d after a 36-hr fasting period, at t h e r m o n e u t r a l temperatures, with the ponies standing at rest,
and the chamber covered to prevent distractions. Additional readings were taken on the ponies standing and either eating or digesting, as described in table 1. Phase 2 of the study was the evaluation of systems and parameters on exercising animals. Subjects were two, 2-year-old pony geldings with an average weight of 204 kilograms. The ponies were exercised daily on a walker at the gait to be studied (walk or trot). Ponies were exercised for 15 min the first day and thereafter time was increased 5 rain a day up to a m a x i m u m of 2 hours. The ponies were worked at the walk or trot 7 days prior to the first reading, and readings were taken every 7 days thereafter for the exercise bouts as described in tables 2 through 4. Oxygen consumption, carbon dioxide production, respiratory quotients, and energy expenditures were obtained using a mask designed to fit over the muzzle of the p o n y and allowed inhalation o f atmospheric air and exhalation and collection of expired air w i t h o u t backflow in the system (figure 2). The mask was made of light plexiglass with two sets of one-way rubber valves adapted from the design of Daniels (1971). The six, 1-inch intake valves were spaced around the perimeter of the mask and allowed over three times the average ventilation area of a horse's trachea. The f o u r 1-inch exit valves were positioned on the b o t t o m of the mask and allowed over twice the normal ventilation area for exhalation. Upon inhalation, the intake valves opened allowing inspiration of atmo-
TABLE 1. ENERGETICS IN CLOSED CHAMBER Calc. SMR = 60.49 Kcal/hr a Calc. SMR = 71.06 Kcal/hr
Foal #1, wt 54.88 kg Foal #2, wt 68.03 kg
0 2
Activities Standard metabolic rate Standing with feed and water but not eating Standing and eating Standing and eating Standard metabolic rate Standing soon after eating Standing and eating Standing, 5 hr after eating aKleiber, M. 1961.
Foal no.
consumption (L/hr)
RO.
1
11.54
1.43
1 1 1 2 2 2 2
22.72 31.84 33.30 12.24 24.06 32.28 31.15
1.08 .77 1.09
1.77 .97 .87 1.26
Kcal/hr 63.51 116.06 151.60 171.23 72.28 120.04 157.24 166.21
Kcal/ hr/kg 1.16
2.11 2.76 3.12 1.06 1.76
2.31 2.44
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Figure 1. Metabolism Chamber.
1667
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BURKE AND ALBERT
RESULTS AND DISCUSSION
Figure 2. Face mask for measuring oxygen consumption and carbon dioxide production.
spheric air, while the exit valves were drawn closed. When the animal exhaled, the intake valves were forced shut, leaving the exit valves as the only route for expired air. Expired air then ran through hoses attached to the bottom plate of the mask, to a flow meter, and into teflon gas collection bags. The top of the mask was lined with foam rubber to insure an air tight fit and for the comfort of the animal. Wet bulb and dry bulb temperatures of both inspired and expired air were measured to allow accurate calculations under standard conditions (STPD). Heart rates and heart recovery rates were monitored as indicators of physical fitness. Recovery rate was defined as the "before" to "after" exercise heart rate change in beats divided by the time required for thc animal to recover its resting heart rate: Recover), Rate (beats/rain) = "after" heart rate - "before" heart rate (beats)/time to recover resting rate (rain). Heart rates of ponies were monitored by using a stethescope, but in later studies with horses arterial pulse or a single channel electrocardiogram recorder were used.
The results of the first phase of the study arc shown in table 1. Calculated standard metabolic rate using body weight (kg) "75 closely approximated measured values in both subjects, 6 0 . 4 9 vs 63.51 kcal/hr and 71.06 vs 72.28 keal/hr. Expressed as kcal/hr/kg, the SMR values were 1.16 and 1.06, which is greater than the .736 reported by Brody (1945) in horses, but agrees closely with the observations of Winchester
Figure 3. Excising muscle biopsy with KoffierLillie septum clamp.
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Muscle biopsies were taken from the biceps fcmoris before and after exercise, and upon cardiac recovery. Biopsies were analyzed for Iactic acid concentrations using Sigma Chemical Company Procedure #826-UV. The biceps femoris was chosen since it is used in all the gaits of the horse and is massive enough to allow numerous biopsies without any lameness or permanent injury. The first step in the biopsy procedure was clcaning the skin area with phisohex and anesthetizing a 1-inch by 2-inch area with Lidocaine plus epinephrine subdermally, taking care to avoid penetrating the muscle fascia. Two minutes were allowed for the anesthetic to take effect, thcn a stab incision was made with a scalpel through thc skin and fascia. The muscle sample was excised using a Koffler-Lillic septum clamp (Mueller and Co., Chicago, IL) (figure 3) added to cold pcrchoric acid, homogenized, and kept frozen until analysis. In this study, muscle samples weighed between 150 and 200 rag.
MEASURING CONDITION A N D ENERGY COST IN HORSES
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1669
BURKE AND ALBERT
1670
TABLE 3. HEART RATES (PER MINUTE) a Time to cardiac recovery
Before
After
(rain)
~&-hrwalk l-hr walk 188 walk 88 trot ~&-hrtrot 3,~-hrtrot
54 47 46 49 54 45
60 64 53 63 70 66
20.5 23.0 17.5 18.5 25.0 17.5
+- 1.00 • 1.00 +- 2.00 + 3.00 -+ 4.00 • 4.00
-+ 2.00 -+ 3.00 +- 1.00 • 2.00 + 4.00 + 1.00
• 1.5 +- 2.0 • 2.5 + 4.0 • 3.0 -+ 2.5
(beats/ min) .29 .74 .40 .76 .64 1.20
+- .12 + .01 + .01 • .14 + .44 • .17
aEach value is the mean of a single determination on two animals.
(1943) and Nadal'jak (1962), who reported values o f 1.20 a n d 1.32 k c a l / h r / k g , respectively, for horses s t a n d i n g at rest. T h e increase in energy e x p e n d i t u r e over S M R for t h e average o f t h e s t a n d i n g - e a t i n g d a t a is 130% for t h e first p o n y a n d 105% for t h e second. R e s p i r a t o r y q u o t i e n t s were in a range o f .77 to 1.77, i n d i c a t i n g t h e range to b e e x p e c t e d w h e n using t h e mask o n exercising animals. T h e o r e t i c a l l y , r e s p i r a t o r y q u o t i e n t s for a n i m a l s using exclusively c a r b o h y d r a t e s , p r o t e i n , or fats are 1.00, .83, or .71, respectively. T h e d a t a suggested t h a t the p o n i e s were using c a r b o h y drates as t h e i r m a i n energy source, as t h e i r R Q values were generally near 1.00. R Q v a l u e s over 1.00 o c c u r in a n i m a l s at rest w h e n t h e y are actively c o n v e r t i n g b o d y c a r b o h y d r a t e t o fat. This process yields c o n s i d e r a b l e a m o u n t s o f m e t a b o l i c oxygen, w h i c h is used in t h e oxidation o f o t h e r s u b s t a n c e a n d r e d u c e s t h e observed r e s p i r a t o r y o x y g e n c o n s u m p t i o n . T h e n e t result is an increase in r e s p i r a t o r y q u o t i e n t . T h e results o f t h e s t u d y o n exercise are s h o w n in t a b l e 2. T h e data are t h e average o f t w o ponies, w h o s e average w e i g h t was 2 0 4
kilograms. T h e readings for t h e 1 / 2 - h r walk were t a k e n b e f o r e training, t h e 1 h r walk readings t a k e n a f t e r 2 weeks, a n d t h e 1 1/4 hr readings t a k e n a f t e r 3 weeks o f training. T h e data at t h e t r o t were t a k e n weekly t h e r e a f t e r as previously described. O x y g e n c o n s u m p t i o n ranged f r o m .28 l i t e r / h r / k g at rest to 1.66 l i t e r / h r / k g at t h e walk, a n d f r o m .25 l i t t e r / h r / kg a t rest to 1.97 l i t e r / h r / k g a f t e r a 1/2-hr trot. Data o b t a i n e d on h u m a n s u b j e c t s o n e i t h e r a bicycle e r g o m e t e r or t r e a d m i l l varies f r o m 1.90 l i t e r / h r / k g ( P r a m p e r o e t a l . , 1 9 7 0 ) for subm a x i m a l exercise to 3.55 l i t e r / h r / k g ( H e r m a n sen a n d Saltin, 1 9 6 8 ) a n d 4.43 l i t e r / h r / k g ( E k b l o m a n d H e r m a n s e n , 1 9 6 8 ) for m a x i m a l o x y g e n u p t a k e s . This w o u l d suggest t h a t all b o u t s o f exercise i n c l u d e d in this s t u d y were s u b m a x i m a l for t h e ponies. Energy e x p e n d i t u r e for a s t a n d i n g - f e d subject was 118% over S M R in t h e c h a m b e r (table 1) and 110% over calculated S M R using t h e mask. T h e energy cost for t h e p o n i e s b e f o r e exercise while s t a n d i n g at rest was 1.66 kcal/ hr/kg, w h i c h closely a p p r o x i m a t e s t h e calculated m a i n t e n a n c e r e q u i r e m e n t o f t h e p o n i e s
TABLE 4. MUSCLE LACTIC ACID CONCENTRATION a (ttg/g muscle)
Exercise
Before
tA-hr walk 1-hr walk 1 88 88 trot %-hr trot
5.117 5.068 4.923 4.923 4.200
Cardiac recovery
After -+ 1.21 + 1.10 + .94 + 1.66 + 2.61
9.122 10.860 16.51 .304 .579
aEach value is the mean of a single determination on two animals.
+- 3.67 +- 4.71 + 5.65 • .18 • .07
7 . 7 6 7 + 1.50
7.240 8.398 5.358 1.738
+- 1.94 +- 2.01 + 3.04 -+ 1.04
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Exercise
Recovery rate
MEASURING CONDITION AND ENERGY COST IN HORSES
athletes, even upon the mildest exertion (Bergstrom et al., 1971; Huckabee, 1958), while other workers report the need to surpass an aerobic threshold before any lactic acid accumulates (Wassermann e t al., 1965; Schneider e t al., 1968). Lactic acid concentration in the muscle decreased after trotting for 1 / 4 - a n d 1/2-hr periods, returning towards resting values upon cardiac recovery. The disappearance of lactic acid has been explained in numerous ways. L. Hermansen ( u n p u b l i s h e d d a t a ) s u g gested lactic acid can be resynthesized to glucose within the muscle at a rate sufficient to explain the disappearance of lactic acid. Rowell e t al. (1966) demonstrated the importance of the liver and gluconeogenesis in the removal of lactic acid from the blood. The techniques investigated for measuring energy expenditure and physical fitness show promise and will provide the basis for further research in equine exercise physiology. LITERATURE CITED
Armsby, H. P. 1903. Principles of Animal Nutrition. John Wiley and Sons, New York. Bergstrom, J., G. Guarnieri, and E. Huhman. 1971. Carbohydrate metabolsim and electrolyte changes in human muscle tissue during heavy work. J. Appl. Physiol. 30:122-125. Brody, S. B. 1945. Bioenergeties and Growth. Reinhold Publishing Corp., New York. Brody, S. B. and E. A. Trowbridge. 1937. Efficiency of horses, men and motors. Univ. of Missouri Agr. Exp. Star. Bull. #244. Brouwer, E. 1965. Report of subcommittee of E.A.A.P. on constantS and factors. In K. L. Blaxter, (Ed.) Energy Metabolism, Academic Press, New York. Costill, D. L. 1970. Metabolic responses during distanee running. J. Appl. Physiol., 28:251. Cureton, T. K. 1948. Variations in a single subject of oxygen intake, acetylene minute volume, oxygen debt, RQ, in 12 various exercises designed as t e s t S of maximal circulatory capacity. Amer. J. Physiol., 155:431. Daniels, J. 1971. Portable respiratory gas collection equipment. J. Appl. Physiol., 31 (1): 164. Doroschuk, E., E. Bernauer, J. Bosco and T. K. Cureton. 1963. Prediction of all-out treadmill running time in young boys in the SportS-Fimess School, University of Illinois. Australian J. Phys. Educ. #29: 36-40. Ekblom, B., and L. Hermansen. 1968. Cardiac output in athletes. J. Appl. Physiol. 25:619. Hall, W. C. and S. B. Brody. 1934. The energy cost of horizontal walking in cattle and horses of various ages and body weights. Univ.of Missouri Agr. Exp. State. Bull. #208. Henry, F. M. 1950. Physiological and performance changes in Athletic conditioning. J. AppI. Physiol. 3:103.
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according to the formula recommended by N.R.C. (1973); DE (kcal) = 155 x W (kg) -Ts, which is 1.71 kcal/hr/kg. The average increment of walking over standing was 3.31 kcal/hr/kg, which is much greater than the increment of 1.70 kcal/hr/kg reported by Hall and Brody (1934). The percent increase from standing to walking for the ponies averaged 160%. The cost of walking above maintenance averaged 3.88 kcal/hr/kg, which is between the values for walking (.5 kcal/hr/kg) and light work (5.1 kcal/hr/kg) reported by Hintz et al. (1971). The energy cost of trotting over standing averaged 4.60 keal/hr/kg, slightly under the "light work" value of 5.1 kcal/hr/kg from Hintz e t al. (1971). The ratio of work energy expenditure to basal energy expenditure ranged from 2 to 12.5. The ratio of work energy to resting energy varied from 3 to 6.5, which is comparable to the lower half of the maximum range reported by Brody and Trowbridge (1937) of work: basal energy = 21 and work:rest energy = 15. Respiratory quotients before exercise averaged 1.15 during readings at the walk, and .95 before working at the trot. RQ also decreased during longer exercise and was low during recovery, suggesting increased utilization of fat as a major energy source. This trend for RQ to decrease through training and during long submaximal exercise has been demonstrated in human athletes (Michael and Cureton, 1953; Costill, 1970). Similar trends were also reported by Margaria e t al. (1933) for long exercise at slow rates, but their study also showed an increase in RQ during short duration, severe exercise, as did a study by Cureton (1948). Studies now in progress at the University of Illinois show comparable trends in horses. Heart rate and heart recovery data are summarized in table 3. tleart rate increased as would be expected for all exercise bouts, more so at the trot than at the walk. Recovery time shows no apparent trend, though recovery rate tended to increase through training, indicating improved physical condition. Similar findings have been reported in humans, (Knehr et al., 1942; Henry, 1950), where resting heart rate decreased and heart recovery rate increased as subjects trained. Muscle lactic acid concentration (table 4) increased for all bouts of walking, and showed greater increases during longer exercise. Lactic acid accumulation has been reported in human
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BURKE AND ALBERT terly, 24:446. Nadal'jak, E. A. 1962. Effect of state of training on gaseous exchange and energy expenditure in horses o f heavy draft breed. Nutr. Abstr. and Rev., 32:463. N.R.C. 1973. Nutrient Requirements of Domestic Animals, No. 6. Nutrient Requirements of Horses. National Research Council, Washington, DC. Prampero, P. E. Di, C. T. M. Davies, P. Cerretelli and R. Margaria. 1970. An analysis of oxygen debt contracted in submaximal exercise. J. Appl. Physiol. 29: 547. Rowell, L. B., K. K. Kraning, T. O. Evans, J. W. Kennedy, J. R. Blackmon and F. Kusumi. 1966. Splanchnic removal o f lactate and pyruvate during prolonged exercise in man. J. Appl. Physiol., 21:1773. Schneider, E. G., S. Robinson and J. L. Newton. 1968. Oxygen diet in anaerobic work. J. Appl. Physiol., 25:58. Wasserman, K., G. G. Burton and A. L. Van Kess. 1965. Excess lactate and oxygen debt o f exercise. J. Appl. Physiol., 20:1299. Winchester, C. F. 1943. The energy cost o f standing in horses. Sci. 97:24.
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Hermansen, L., and B. Saltin. 1969. Oxygen uptake during maximal treadmill and bicycle exercise. J. Appl. Physiol. 26:31. Hintz, H. F., S. J. Roberts, S. W. Sabin and It. F. Schryver. 1971. Energy requirements of light horses for various activities. J. Anita. Sci. 32:100. Huekabee, W. E. 1958. Relationships o f pyruvate and lactate during anaerobic metabolism. J. Clin. Invest., 37:244-271. Kleiber, M. 1961. The Fire of Life: An Introduction to Animal Energetics. John Wiley and Sons, Inc., New York. Knehr, C. A., D. B. Dill and W. Newfeld. 1942. Training and its effect on man at rest and at work. Amer. J. Physiol., 136:148-156. Margaria, R., P. Cerretelli, P. Aghemo and G. Sassi. 1963. Energy cost o f running. J. Appl. Physiol., 18:367. Matgaria, R., H. T. Edwards and D. B. Dill. 1933. The possible mechanisms of contracting and paying oxygen debt and the role of lactic acid in muscular contraction. Amer. J. Physiol. 106:689. Michael, E. D. and T. K. Cureton. 1953. Effects of physical training on cardiac output at ground level and 15,000 feet simulated aldtud. Research Quar-
University o f Illinois, Urbana 61801
SUMMARY Methods for determining oxygen consumption and carbon dioxide production (respiratory quotient), heart rates and heart recovery rates, and muscle lactic acid production adapted from human studies were evaluated for measurement of energy expenditure and physical condition in horses. Standard metabolic rate (SMR) and energy use of two weanling ponies were determined by indirect calorimetry in a metabolism chamber to test the adequacy of the apparatus to be used on exercising animals. Ponies of 55 and 68 kg had calculated SMR's of 60.49 and 71.06 Kcal/hr, compared to measured values of 63.51 and 72.28 kcal/hr, respectively. Chamber values for oxygen consumption ranged from 11.54 to 33.30 liter/hr and R Q values were within an acceptable range, from .77 to 1.77. 02 consumption values obtained on exercising animals with a specially designed face mask ranged from 50.76 liter/min before exercise to 401.40 liter/rain after a 1/2 hr trot, with R Q range from .55 to 1.56. Resting heart rate tended to decrease and recovery rate to increase through training. Muscle lactic acid concentration increased from approximately 5 /ag/g of muscle at rest to 9.12, 10.86 and 16.51 /~g/g for 1/2 hr, 1 hr, and 1 1/4 hr bouts of walking, respectively. Lactic acid concentration after 1/4 hr and 1/2 hr bouts of trotting decreased t o . 30 a n d . 50 #gig. (Key Words: Horse, Energy Expenditure, Recovery Rate.)
equine athletes with maximum utilization of feed energy. Also, there is a need to determine the energy costs for more specifically defined activities than the customary categories of light, medium, and heavy work. Work in humans by Henry (1950) and Doroschuk et al. (1963) demonstrated the superiority of physiological parameters over p e r f o r m a n c e parameters in measuring improved physical condition due to training. Since the early works of Zuntz (from Armsby, 1903), Hall and Brody (1934) and Brody and Trowbridge (1937), there has been little work done on horses in these areas. The most recent and most significant body of research on physical conditioning and energy cost in exercise has been done on human athletes (Cureton et aL, 1948; Michael and Cureton, 1953; Margaria et al., 1963). This study was designed to evaluate certain physiological parameters adapted from studies on human athletes for use in measuring physical fitness and energy expenditure in horses. Oxygen consumption and respiratory quotient were used to calculate caloric expenditure. Heart rates, heart recovery times, and heart recovery rates were used as indicators of physical condition. Muscle lactic acid concentration was used to determine the metabolic state of the muscles as a possible indication of oxygen debt.
EXPERIMENTAL PROCEDURES
Phase 1 of this study was intended to obtain precise measures of standard metabolic rate, respiratory quotient, and energy use of a INTRODUCTION standing-fed subject. Two 5-month-old ponies Methods for determining physical condition weighing 54.88 kg and 63.08 kg were placed individually into a closed chamber with air tight and energy expenditure in horses are important, plexiglass sides and closely monitored temperasince optimal performance is desired from our ture and humidity (figure 1). Oxygen consumption and carbon dioxide production of the ponies were measured by running two standard 1Current address: 106 Stock Pavilion, Urbana, IL gases, outside air, room air and chamber air 61801. 2Current address: 104 Stock Pavilion, Urbana, IL through Beckman paramagnetic oxygen and 61801. infrared carbon dioxide analyzers. Respiratory 1666 JOURNAL OF ANIMAL SCIENCE, Vol. 46, No. 6, 1978
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D. J. Burke 1 and W. W. Albert 2
MEASURING CONDITION AND ENERGY COST IN HORSES
quotients and energy expenditures were calculated f r o m the following formulas: Respiratory Q u o t i e n t = liters of carbon dioxide p r o d u c e d / liters of o x y g e n consumed: Energy e x p e n d e d (kcal) = 3.866 (liters 02 c o n s u m e d ) + 1.200 (liters CO2 p r o d u c e d ) / - 1 . 4 3 1 (grams N excreted in urine); (Brouwer, 1965). Urinary nitrogen excretion was estimated from data of G. L. Heusner (unpublished data). The ponies were allowed 3 days to acclimate to the chamber, and the trials were run randomly. The standard metabolic rate was d e t e r m i n e d after a 36-hr fasting period, at t h e r m o n e u t r a l temperatures, with the ponies standing at rest,
and the chamber covered to prevent distractions. Additional readings were taken on the ponies standing and either eating or digesting, as described in table 1. Phase 2 of the study was the evaluation of systems and parameters on exercising animals. Subjects were two, 2-year-old pony geldings with an average weight of 204 kilograms. The ponies were exercised daily on a walker at the gait to be studied (walk or trot). Ponies were exercised for 15 min the first day and thereafter time was increased 5 rain a day up to a m a x i m u m of 2 hours. The ponies were worked at the walk or trot 7 days prior to the first reading, and readings were taken every 7 days thereafter for the exercise bouts as described in tables 2 through 4. Oxygen consumption, carbon dioxide production, respiratory quotients, and energy expenditures were obtained using a mask designed to fit over the muzzle of the p o n y and allowed inhalation o f atmospheric air and exhalation and collection of expired air w i t h o u t backflow in the system (figure 2). The mask was made of light plexiglass with two sets of one-way rubber valves adapted from the design of Daniels (1971). The six, 1-inch intake valves were spaced around the perimeter of the mask and allowed over three times the average ventilation area of a horse's trachea. The f o u r 1-inch exit valves were positioned on the b o t t o m of the mask and allowed over twice the normal ventilation area for exhalation. Upon inhalation, the intake valves opened allowing inspiration of atmo-
TABLE 1. ENERGETICS IN CLOSED CHAMBER Calc. SMR = 60.49 Kcal/hr a Calc. SMR = 71.06 Kcal/hr
Foal #1, wt 54.88 kg Foal #2, wt 68.03 kg
0 2
Activities Standard metabolic rate Standing with feed and water but not eating Standing and eating Standing and eating Standard metabolic rate Standing soon after eating Standing and eating Standing, 5 hr after eating aKleiber, M. 1961.
Foal no.
consumption (L/hr)
RO.
1
11.54
1.43
1 1 1 2 2 2 2
22.72 31.84 33.30 12.24 24.06 32.28 31.15
1.08 .77 1.09
1.77 .97 .87 1.26
Kcal/hr 63.51 116.06 151.60 171.23 72.28 120.04 157.24 166.21
Kcal/ hr/kg 1.16
2.11 2.76 3.12 1.06 1.76
2.31 2.44
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Figure 1. Metabolism Chamber.
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BURKE AND ALBERT
RESULTS AND DISCUSSION
Figure 2. Face mask for measuring oxygen consumption and carbon dioxide production.
spheric air, while the exit valves were drawn closed. When the animal exhaled, the intake valves were forced shut, leaving the exit valves as the only route for expired air. Expired air then ran through hoses attached to the bottom plate of the mask, to a flow meter, and into teflon gas collection bags. The top of the mask was lined with foam rubber to insure an air tight fit and for the comfort of the animal. Wet bulb and dry bulb temperatures of both inspired and expired air were measured to allow accurate calculations under standard conditions (STPD). Heart rates and heart recovery rates were monitored as indicators of physical fitness. Recovery rate was defined as the "before" to "after" exercise heart rate change in beats divided by the time required for thc animal to recover its resting heart rate: Recover), Rate (beats/rain) = "after" heart rate - "before" heart rate (beats)/time to recover resting rate (rain). Heart rates of ponies were monitored by using a stethescope, but in later studies with horses arterial pulse or a single channel electrocardiogram recorder were used.
The results of the first phase of the study arc shown in table 1. Calculated standard metabolic rate using body weight (kg) "75 closely approximated measured values in both subjects, 6 0 . 4 9 vs 63.51 kcal/hr and 71.06 vs 72.28 keal/hr. Expressed as kcal/hr/kg, the SMR values were 1.16 and 1.06, which is greater than the .736 reported by Brody (1945) in horses, but agrees closely with the observations of Winchester
Figure 3. Excising muscle biopsy with KoffierLillie septum clamp.
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Muscle biopsies were taken from the biceps fcmoris before and after exercise, and upon cardiac recovery. Biopsies were analyzed for Iactic acid concentrations using Sigma Chemical Company Procedure #826-UV. The biceps femoris was chosen since it is used in all the gaits of the horse and is massive enough to allow numerous biopsies without any lameness or permanent injury. The first step in the biopsy procedure was clcaning the skin area with phisohex and anesthetizing a 1-inch by 2-inch area with Lidocaine plus epinephrine subdermally, taking care to avoid penetrating the muscle fascia. Two minutes were allowed for the anesthetic to take effect, thcn a stab incision was made with a scalpel through thc skin and fascia. The muscle sample was excised using a Koffler-Lillic septum clamp (Mueller and Co., Chicago, IL) (figure 3) added to cold pcrchoric acid, homogenized, and kept frozen until analysis. In this study, muscle samples weighed between 150 and 200 rag.
MEASURING CONDITION A N D ENERGY COST IN HORSES
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BURKE AND ALBERT
1670
TABLE 3. HEART RATES (PER MINUTE) a Time to cardiac recovery
Before
After
(rain)
~&-hrwalk l-hr walk 188 walk 88 trot ~&-hrtrot 3,~-hrtrot
54 47 46 49 54 45
60 64 53 63 70 66
20.5 23.0 17.5 18.5 25.0 17.5
+- 1.00 • 1.00 +- 2.00 + 3.00 -+ 4.00 • 4.00
-+ 2.00 -+ 3.00 +- 1.00 • 2.00 + 4.00 + 1.00
• 1.5 +- 2.0 • 2.5 + 4.0 • 3.0 -+ 2.5
(beats/ min) .29 .74 .40 .76 .64 1.20
+- .12 + .01 + .01 • .14 + .44 • .17
aEach value is the mean of a single determination on two animals.
(1943) and Nadal'jak (1962), who reported values o f 1.20 a n d 1.32 k c a l / h r / k g , respectively, for horses s t a n d i n g at rest. T h e increase in energy e x p e n d i t u r e over S M R for t h e average o f t h e s t a n d i n g - e a t i n g d a t a is 130% for t h e first p o n y a n d 105% for t h e second. R e s p i r a t o r y q u o t i e n t s were in a range o f .77 to 1.77, i n d i c a t i n g t h e range to b e e x p e c t e d w h e n using t h e mask o n exercising animals. T h e o r e t i c a l l y , r e s p i r a t o r y q u o t i e n t s for a n i m a l s using exclusively c a r b o h y d r a t e s , p r o t e i n , or fats are 1.00, .83, or .71, respectively. T h e d a t a suggested t h a t the p o n i e s were using c a r b o h y drates as t h e i r m a i n energy source, as t h e i r R Q values were generally near 1.00. R Q v a l u e s over 1.00 o c c u r in a n i m a l s at rest w h e n t h e y are actively c o n v e r t i n g b o d y c a r b o h y d r a t e t o fat. This process yields c o n s i d e r a b l e a m o u n t s o f m e t a b o l i c oxygen, w h i c h is used in t h e oxidation o f o t h e r s u b s t a n c e a n d r e d u c e s t h e observed r e s p i r a t o r y o x y g e n c o n s u m p t i o n . T h e n e t result is an increase in r e s p i r a t o r y q u o t i e n t . T h e results o f t h e s t u d y o n exercise are s h o w n in t a b l e 2. T h e data are t h e average o f t w o ponies, w h o s e average w e i g h t was 2 0 4
kilograms. T h e readings for t h e 1 / 2 - h r walk were t a k e n b e f o r e training, t h e 1 h r walk readings t a k e n a f t e r 2 weeks, a n d t h e 1 1/4 hr readings t a k e n a f t e r 3 weeks o f training. T h e data at t h e t r o t were t a k e n weekly t h e r e a f t e r as previously described. O x y g e n c o n s u m p t i o n ranged f r o m .28 l i t e r / h r / k g at rest to 1.66 l i t e r / h r / k g at t h e walk, a n d f r o m .25 l i t t e r / h r / kg a t rest to 1.97 l i t e r / h r / k g a f t e r a 1/2-hr trot. Data o b t a i n e d on h u m a n s u b j e c t s o n e i t h e r a bicycle e r g o m e t e r or t r e a d m i l l varies f r o m 1.90 l i t e r / h r / k g ( P r a m p e r o e t a l . , 1 9 7 0 ) for subm a x i m a l exercise to 3.55 l i t e r / h r / k g ( H e r m a n sen a n d Saltin, 1 9 6 8 ) a n d 4.43 l i t e r / h r / k g ( E k b l o m a n d H e r m a n s e n , 1 9 6 8 ) for m a x i m a l o x y g e n u p t a k e s . This w o u l d suggest t h a t all b o u t s o f exercise i n c l u d e d in this s t u d y were s u b m a x i m a l for t h e ponies. Energy e x p e n d i t u r e for a s t a n d i n g - f e d subject was 118% over S M R in t h e c h a m b e r (table 1) and 110% over calculated S M R using t h e mask. T h e energy cost for t h e p o n i e s b e f o r e exercise while s t a n d i n g at rest was 1.66 kcal/ hr/kg, w h i c h closely a p p r o x i m a t e s t h e calculated m a i n t e n a n c e r e q u i r e m e n t o f t h e p o n i e s
TABLE 4. MUSCLE LACTIC ACID CONCENTRATION a (ttg/g muscle)
Exercise
Before
tA-hr walk 1-hr walk 1 88 88 trot %-hr trot
5.117 5.068 4.923 4.923 4.200
Cardiac recovery
After -+ 1.21 + 1.10 + .94 + 1.66 + 2.61
9.122 10.860 16.51 .304 .579
aEach value is the mean of a single determination on two animals.
+- 3.67 +- 4.71 + 5.65 • .18 • .07
7 . 7 6 7 + 1.50
7.240 8.398 5.358 1.738
+- 1.94 +- 2.01 + 3.04 -+ 1.04
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Exercise
Recovery rate
MEASURING CONDITION AND ENERGY COST IN HORSES
athletes, even upon the mildest exertion (Bergstrom et al., 1971; Huckabee, 1958), while other workers report the need to surpass an aerobic threshold before any lactic acid accumulates (Wassermann e t al., 1965; Schneider e t al., 1968). Lactic acid concentration in the muscle decreased after trotting for 1 / 4 - a n d 1/2-hr periods, returning towards resting values upon cardiac recovery. The disappearance of lactic acid has been explained in numerous ways. L. Hermansen ( u n p u b l i s h e d d a t a ) s u g gested lactic acid can be resynthesized to glucose within the muscle at a rate sufficient to explain the disappearance of lactic acid. Rowell e t al. (1966) demonstrated the importance of the liver and gluconeogenesis in the removal of lactic acid from the blood. The techniques investigated for measuring energy expenditure and physical fitness show promise and will provide the basis for further research in equine exercise physiology. LITERATURE CITED
Armsby, H. P. 1903. Principles of Animal Nutrition. John Wiley and Sons, New York. Bergstrom, J., G. Guarnieri, and E. Huhman. 1971. Carbohydrate metabolsim and electrolyte changes in human muscle tissue during heavy work. J. Appl. Physiol. 30:122-125. Brody, S. B. 1945. Bioenergeties and Growth. Reinhold Publishing Corp., New York. Brody, S. B. and E. A. Trowbridge. 1937. Efficiency of horses, men and motors. Univ. of Missouri Agr. Exp. Star. Bull. #244. Brouwer, E. 1965. Report of subcommittee of E.A.A.P. on constantS and factors. In K. L. Blaxter, (Ed.) Energy Metabolism, Academic Press, New York. Costill, D. L. 1970. Metabolic responses during distanee running. J. Appl. Physiol., 28:251. Cureton, T. K. 1948. Variations in a single subject of oxygen intake, acetylene minute volume, oxygen debt, RQ, in 12 various exercises designed as t e s t S of maximal circulatory capacity. Amer. J. Physiol., 155:431. Daniels, J. 1971. Portable respiratory gas collection equipment. J. Appl. Physiol., 31 (1): 164. Doroschuk, E., E. Bernauer, J. Bosco and T. K. Cureton. 1963. Prediction of all-out treadmill running time in young boys in the SportS-Fimess School, University of Illinois. Australian J. Phys. Educ. #29: 36-40. Ekblom, B., and L. Hermansen. 1968. Cardiac output in athletes. J. Appl. Physiol. 25:619. Hall, W. C. and S. B. Brody. 1934. The energy cost of horizontal walking in cattle and horses of various ages and body weights. Univ.of Missouri Agr. Exp. State. Bull. #208. Henry, F. M. 1950. Physiological and performance changes in Athletic conditioning. J. AppI. Physiol. 3:103.
Downloaded from https://academic.oup.com/jas/article-abstract/46/6/1666/4699286 by Iowa State University user on 18 January 2019
according to the formula recommended by N.R.C. (1973); DE (kcal) = 155 x W (kg) -Ts, which is 1.71 kcal/hr/kg. The average increment of walking over standing was 3.31 kcal/hr/kg, which is much greater than the increment of 1.70 kcal/hr/kg reported by Hall and Brody (1934). The percent increase from standing to walking for the ponies averaged 160%. The cost of walking above maintenance averaged 3.88 kcal/hr/kg, which is between the values for walking (.5 kcal/hr/kg) and light work (5.1 kcal/hr/kg) reported by Hintz et al. (1971). The energy cost of trotting over standing averaged 4.60 keal/hr/kg, slightly under the "light work" value of 5.1 kcal/hr/kg from Hintz e t al. (1971). The ratio of work energy expenditure to basal energy expenditure ranged from 2 to 12.5. The ratio of work energy to resting energy varied from 3 to 6.5, which is comparable to the lower half of the maximum range reported by Brody and Trowbridge (1937) of work: basal energy = 21 and work:rest energy = 15. Respiratory quotients before exercise averaged 1.15 during readings at the walk, and .95 before working at the trot. RQ also decreased during longer exercise and was low during recovery, suggesting increased utilization of fat as a major energy source. This trend for RQ to decrease through training and during long submaximal exercise has been demonstrated in human athletes (Michael and Cureton, 1953; Costill, 1970). Similar trends were also reported by Margaria e t al. (1933) for long exercise at slow rates, but their study also showed an increase in RQ during short duration, severe exercise, as did a study by Cureton (1948). Studies now in progress at the University of Illinois show comparable trends in horses. Heart rate and heart recovery data are summarized in table 3. tleart rate increased as would be expected for all exercise bouts, more so at the trot than at the walk. Recovery time shows no apparent trend, though recovery rate tended to increase through training, indicating improved physical condition. Similar findings have been reported in humans, (Knehr et al., 1942; Henry, 1950), where resting heart rate decreased and heart recovery rate increased as subjects trained. Muscle lactic acid concentration (table 4) increased for all bouts of walking, and showed greater increases during longer exercise. Lactic acid accumulation has been reported in human
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BURKE AND ALBERT terly, 24:446. Nadal'jak, E. A. 1962. Effect of state of training on gaseous exchange and energy expenditure in horses o f heavy draft breed. Nutr. Abstr. and Rev., 32:463. N.R.C. 1973. Nutrient Requirements of Domestic Animals, No. 6. Nutrient Requirements of Horses. National Research Council, Washington, DC. Prampero, P. E. Di, C. T. M. Davies, P. Cerretelli and R. Margaria. 1970. An analysis of oxygen debt contracted in submaximal exercise. J. Appl. Physiol. 29: 547. Rowell, L. B., K. K. Kraning, T. O. Evans, J. W. Kennedy, J. R. Blackmon and F. Kusumi. 1966. Splanchnic removal o f lactate and pyruvate during prolonged exercise in man. J. Appl. Physiol., 21:1773. Schneider, E. G., S. Robinson and J. L. Newton. 1968. Oxygen diet in anaerobic work. J. Appl. Physiol., 25:58. Wasserman, K., G. G. Burton and A. L. Van Kess. 1965. Excess lactate and oxygen debt o f exercise. J. Appl. Physiol., 20:1299. Winchester, C. F. 1943. The energy cost o f standing in horses. Sci. 97:24.
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Hermansen, L., and B. Saltin. 1969. Oxygen uptake during maximal treadmill and bicycle exercise. J. Appl. Physiol. 26:31. Hintz, H. F., S. J. Roberts, S. W. Sabin and It. F. Schryver. 1971. Energy requirements of light horses for various activities. J. Anita. Sci. 32:100. Huekabee, W. E. 1958. Relationships o f pyruvate and lactate during anaerobic metabolism. J. Clin. Invest., 37:244-271. Kleiber, M. 1961. The Fire of Life: An Introduction to Animal Energetics. John Wiley and Sons, Inc., New York. Knehr, C. A., D. B. Dill and W. Newfeld. 1942. Training and its effect on man at rest and at work. Amer. J. Physiol., 136:148-156. Margaria, R., P. Cerretelli, P. Aghemo and G. Sassi. 1963. Energy cost o f running. J. Appl. Physiol., 18:367. Matgaria, R., H. T. Edwards and D. B. Dill. 1933. The possible mechanisms of contracting and paying oxygen debt and the role of lactic acid in muscular contraction. Amer. J. Physiol. 106:689. Michael, E. D. and T. K. Cureton. 1953. Effects of physical training on cardiac output at ground level and 15,000 feet simulated aldtud. Research Quar-
