The relationship between body composition, training and race performance in a group of Thoroughbred flat racehorses

Summary Reasons for performing study Few noninvasive measures associated with performance assessment are available for racehorse trainers. Evaluation of body composition of superior human sprinters has revealed a lower fat mass (FM), percentage (%) fat and greater fat‐free mass (FFM), but to date there have been few studies evaluating this in racehorses. Objectives To determine the effects of age, gender and training on body composition and the relationship between body composition, physiological measurements and performance in Thoroughbred racehorses. Methods At 2, 5 and 8 months of training, rump fat thickness (RFT) was ultrasonographically measured in 1‐, 2‐ and 3‐year‐old Thoroughbreds (n = 148), with FM, % fat and FFM calculated. Speed, heart rate, plasma lactate and serum creatine kinase concentrations were recorded during each fast work session. Training duration (number of training days) and intensity (number of fast work sessions) were collated for each training period. Retrospective racing performance was used to categorise horses as elite or nonelite. Results FFM was greater in males (P = 0.006) at all training stages. There were no interactions between training duration, intensity, gender and age (P>0.05); all effects were linear. Training duration had a negative effect on RFT (P = 0.0002), FM (P