Physiological responses of two equine breeds to a tropical winter climate
In tropical regions of Mexico, breed horses introduced from European countries are used for recreational activities under hot and humid conditions without considering their well-being. In order to evaluate the effect of winter conditions on physiological responses of two equine breeds, twelve horses (six Spanish and six Friesian breeds) were evaluated in the western Pacific coast of Mexico. The winter season was divided in 3 periods so that the statistical model included the factors breed and period. The physiological responses evaluated were: heart rate (HR), respiratory rate (RR), capillary refill time (CRT), and rectal temperature (RT). The climatic variables ambient temperature (AT) and relative humidity (RH) were used to estimate the temperature-humidity index (THI). Averages for THI, AT and RH were 71.4 units, 24.3 °C, and 53.4%, respectively. The CRT was similar (P > 0.05) among breeds and periods. The interaction B X P was significant (P < 0.05) for HR, RR, and RT in the second and third periods, but not in the first one. As a result, Spanish horses experimented higher (P < 0.05) HR (38.1 vs 37.6 and 38.0 vs 37.0 beats/min), RR (18.8 vs 18.5 and 18.9 vs 17.4 bpm), and RT (38.1 vs 38.0 °C and 38.0 vs 37.8 °C) than Friesian horses during the second and third periods, respectively. Both breeds of horses were exposed to a mild to moderate heat stress during winter tropical conditions; however, Spanish breed horses showed better tolerance to heat stress than Friesian horses based on their physiological measures evaluated.