D.L. EvansA , H.L. GramkowA , A.D. VermeulenB A 

 Faculty of Veterinary Science, University of Sydney, NSW 2006 B NatureVet Pty Ltd, GPO Box 147 Glenorie, NSW 2157, Australia 

Proc. Aust. Equine Sc. Symp., Vol 1, 2006

Studies of the energetics of Thoroughbred races have confirmed that aerobic energy production is predominant in races exceeding 1200 m distance (Eaton et al., 1995). Maximal oxygen uptake (VO2max) is the gold standard for measurement of the aerobic contribution to energy output. This measurement necessitates use of high speed treadmills and expensive laboratory equipment. The velocities at which horses attain their maximal aerobic energy output and maximal heart rate (HR) are approximately equal in horses. The aim of this project has been to develop a method of measuring the velocity at which maximal HR (VHRmax) is achieved. It was hypothesized that VHRmax could be reliably measured during routine racetrack gallops in Thoroughbreds, and could be used to detect changes in fitness over time during commercial training. The relationship between VHRmax and retrospective racing performance was also investigated. If fitness tests could be conducted with the normal racetrack exercise routines, there may be greater adoption of this approach to fitness testing in racehorses in the commercial setting. Twelve healthy 3 to 5-year-old Thoroughbreds were used in the studies of reliability and the effect of training. Five second averages of velocity and heart rate (HR) were recorded during a typical fast exercise training session, using a global positioning system (GPS) and Polar HR monitor. A standardized exercise test protocol was not used. Regression analyses using trot and gallop data were used to calculate VHRmax and V200 (velocity with HR of 200 bpm). Data were collected on consecutive `fast' day training sessions to assess the reliability of measurements. The effect of training was investigated with fitness tests in weeks 2 and 6 of `fast' training. Absolute and relative differences were calculated to evaluate reliability, and paired t tests were used to detect an effect of training. VHRmax,V200 and HRmax were reliable measurements, with mean differences of 2 % or less. VHRmax and V200 both increased significantly with training (p<0.01), but there was no effect of training on HRmax. Horses with higher VHRmax earned significantly more dollars per race start (r=0.41, P<0.05, n=25). In conclusion, VHRmax can be calculated reliably with measurements of heart rate and GPSderived velocity during field exercise tests in thoroughbred racehorses in commercial exercise training. This approach enables regular monitoring of fitness with field exercise tests in racehorses without use of strict exercise test protocols. The technique also avoids the need for treadmill exercise tests for monitoring fitness in racehorses. Future studies could investigate the use of this approach to fitness testing in other types of equine exercise, and in larger scale prospective studies. 

EATON, M.D., EVANS, D.L., HODGSON, D. R. AND ROSE, R. J. (1995). Effect of treadmill incline and speed on metabolic rate during exercise in Thoroughbred horses. Journal of Applied Physiology 79, 951-957 HARKINS, J.D., BEADLE, R.E. AND KAMERLING, S.G. (1993). The correlation of running ability and physiological variables in Thoroughbred horses. Equine Veterinary Journal 25, 53-60 Acknowledgments. This study was supported by the Rural Industries Research and Development Corporation, Nature Vet Pty Ltd, and Equitronics Technologies Pty Ltd.