Dynamics of heat-shock proteins, metabolic and endocrine responses during increasing temperature humidity index (THI) in lactating Hariana (Zebu) cattle

The present experiment was aimed to study the dynamics of different heat stress responses with increasing stress levels in terms of temperature humidity index (THI) during summer season (April–July). Six lactating Hariana cows were used in the study. Physiological responses were recorded and blood samples were collected fortnightly for the estimation of plasma analytes. THI during the experiment ranged between 73 and 87. A significant (p < 0.05) increase in respiratory rate and pulse rate was observed at a THI of 78 and 80, respectively, whereas milk production declined significantly (p < 0.001) only at THI of 81 and above. HSP70 and HSP90 increased significantly (p < 0.05) and reached at zenith at a THI of 78 and 80 respectively. Cortisol level was significantly (p < 0.05) higher only at a THI of 82 and thereafter declined significantly (p < 0.05). Similarly, total antioxidative capacity increased significantly (p < 0.05) at a THI of 85 only. It can be concluded that in response to heat stress, HSP70 showed a single peak and thereafter declined to normal levels; however, during decreased HSP70 levels, cellular protection against heat stress was taken up by increase in HSP90 levels.