Effects of Different Exercise Intensities During Detraining on Aerobic Capacity in Thoroughbred Horses

Abstract

Introduction Thoroughbred racehorses often experience periods of detraining due to locomotor disorders and subsequent rehabilitation. We hypothesised that regularly exercising horses at different intensities during a period of detraining would differentially maintain their cardiopulmonary and O2 transport capacities. Methods Twenty-seven Thoroughbred horses trained for 18 weeks then underwent 12 weeks of detraining according to one of three protocols: 1) cantering at 70% maximal rate of O2 consumption (VO2max) for 3?min/d for 5?d/wk (C group), 2) walking for 1?h/d for 5?d/wk (W group) and 3) stall rest (S group). Standardised treadmill exercise tests were performed before and after detraining during which cardiopulmonary and O2 transport variables were measured. Data were analysed with two-way ANOVA and pairwise comparisons made with Tukey's test. Significance was defined as P≤0.05. Results Mass-specific VO2max, maximal cardiac output and maximal stroke volume of all groups decreased after detraining with no differences between groups. The run time to exhaustion, speed eliciting VO2max, speed eliciting maximal heart rate and speed at which plasma lactate concentration reached 4?mmol/l of the C group did not change but those of the W and S groups decreased after detraining. Arterial-(mixed-venous) O2 concentration difference did not change after detraining in any group, and maximal heart rate decreased in the W and S groups. Conclusions These results suggest it may be possible to identify a minimum threshold exercise intensity or protocol during detraining in horses that maintains significant elements of performance-related variables and minimises reductions in O2 transport capacity. Ethical Animal Research Protocols for the study were approved by the Animal Welfare and Ethics Committee of the Japan Racing Association (JRA) Equine Research Institute. Sources of funding:?Japan Racing Association. Competing interests:?none.