The Effect of Ambient Temperature, Relative Humidity, and Temperature–Humidity Index on Stress Hormone and Inflammatory Response in Exercising Adult Standardbred Horses

In the present study, the changes in the markers of stress and inflammatory responses of 12 Standardbred horses were investigated before and after exercise during late spring and summer. The environmental temperature, relative humidity, and temperature-humidity index (THI) were assessed during this study. From horses, blood sampling, measurement of heart and respiratory rate (HR and RR), and measurement of rectal temperature (RT) were performed before exercise (Pre) and within 5 min following the end of the exercise (Post). THI values showed mild stress in June and high stress in July. Direct erythrocyte indices statistically increased after exercise compared to the rest condition (p < 0.05). Higher serum cortisol, alpha 1-, alpha 2-, and beta-globulin values were found at Post than at Pre (p < 0.05), whereas lower serum albumin and A/G ratio values were found at Post than at Pre. The HR, RR, and RT statistically increased at Post than at Pre (p < 0.05). The month influenced the values of RR, platelets, cortisol, albumin, alpha 1-, alpha 2-, and beta-globulins (p < 0.05). Overall, the results of this study confirmed the well-recognized physiological response of athletic horses to re-establish homeostasis following exercise.