Effect of weight carriage on work effort in horses

Excessive adiposity in horses is associated with equine metabolic syndrome and laminitis, and additional weight due to fat accumulation may cause further stress on the horse. This study aimed to determine the effect of additional weight carriage on work effort in horses, as estimated by changes in heart rate (HR) and body temperature (Temp). Eight mature mixed-breed horses were paired based on body size in a randomised crossover study. Each day tested a pair of horses with one horse carrying additional weight (15% of body weight; to represent approximately 3 body condition scores) and the other horse serving as a control, with treatments reversed the following week. Heart rate was determined before adding the weight, after a 2 h period of stall rest (prior to the exercise bout), and at the end of a 34 min exercise challenge of walking and trotting on an automated exerciser. Temp was recorded prior to exercise and after the horses were removed from the exerciser. Two-way ANOVA was conducted to determine the effect of exercise and weight carriage on HR and Temp, and paired t-tests were used to compare differences in HR and Temp pre- and post-exercise. HR increased with exercise () and was higher following exercise in horses carrying additional weight (). Exercise increased Temp () and the difference in Temp was greater in the weight-carrying group (). This study documents the effect of weight carriage that could be imposed with body fat, in addition to the known health detriments of adiposity.