The influence of tropical thermal stress on the seasonal and diurnal variations in the physiological and oxidative status of Karan Fries heifers

Abstract

ABSTRACT The changes in plasma cortisol, oxidative status, skin temperature and physiological responses of Karan Fries heifers were monitored during thermoneutral (TN; THI = 73), hot-dry (HD; THI = 83) and hot-humid (HH; THI = 85) seasons. Six heifers (age = 14-I8 months) were followed during each season. All the physiological measures viz. rectal temperature (RT), respiration rate (RR) and pulse rate (PR) displayed a diurnal rhythm and were higher (p < 0.05) in the evening as compared to the morning with maximum variations seen in HH season. The skin temperature (dorsal, abdomen and ear) increased (p ˂ 0.05) in hot seasons mainly in HD as compared to TN season. A significant (p < 0.05) increase was observed in the concentration of plasma cortisol, superoxide dismutase (SOD) and malondialdehyde (MDA) during hot seasons compared to TN season. All the recorded physiological and oxidative parameters were positively correlated with the temperature-humidity index (THI). However, the dry matter intake was negatively correlated with THI during all seasons. The results reveal that the heifers exhibited more signs of heat stress during HD and HH seasons which were reflected by higher concentrations of cortisol, SOD, MDA and more deviation in the normal daily rhythm of various physiological functions.