Influence of Ambient Temperature and Relative Humidity on Recovery from Exercise in Young Horses
Heat stress affects many livestock species, but horses are a particular concern due to the regular exercise they receive. To determine the influence of ambient temperature on exercise recovery in young horses, fourteen Quarter horses (2 to 5 yr; 338 to 540 kg) were utilized in a randomized complete block design. Horses were blocked by BW, age, and sex and randomly assigned to one of two groups that included horses performing a 25 min standardized exercise test at either 0600 h (AM; n=7) or 1300 h (PM; n=7). The ambient temperature for the AM was 23.31°C (83.9% relative humidity), while the ambient temperature for the PM was 34.70°C (40.8% relative humidity). Whole blood lactate (LAC), total plasma protein (TP), heart rate (HR), respiration rate (RR), rectal temperature (RT) and ocular temperature (OT), were obtained immediately following (0 min) exercise, and during a recovery period (5, 15, and 30 min post exercise). Differences in parameters measured were determined using the PROC MIXED procedure in SAS. Clinical parameters including HR, RR, and RT were greater (P = 0.03) in the PM beginning at 5 min of recovery and remained elevated at 30 min post exercise when compared to the AM. Additionally, OT was higher (P ≤ 0.01) in the PM at 0 min and values remained higher through 30 min post exercise. Similar to OT, LAC was greater (P ≤ 0.01) at 0 min in the PM (12.72 ± 1.84 mmol/L) compared to the AM (4.94 ± 1.84 mmol/L), with lactate values in the PM (8.79 ± 1.13 mmol/L) continuing to be greater than the AM (2.25 ± 1.13 mmol/L) at 30 min following exercise. No differences were detected in TP (P = 0.18) between exercise groups, suggesting the exercise intensity did not alter extracellular fluid loss within plasma. RR, OT, and RT remained elevated through recovery, demonstrating an impaired ability to dissipate heat due to the higher ambient temperature during exercise. Lactate values in the PM illustrated that horses exercising at a higher ambient temperature required an increased recovery time due to the increased demands of anaerobic metabolism. Understanding the physiological responses during recovery of exercise at different temperatures may enable industry professionals to adapt daily exercise regimens to better prepare the equine athlete to perform at their full potential.
Heat stress, Exercise, Equine