Impact of thermal stress on physiological, behavioural and biochemical parameters in native and crossbred goats

Abstract

The present study was undertaken to investigate the association of the temperature-humidity index with physiological, biochemical and behavioural responses in Malabari, crossbred and Attappady black goats of Kerala, India. A positive correlation was noticed between in-house temperature (IT) and temperature-humidity index (THI) with respiration rates, rectal temperatures, heart rate and skin temperature levels of breeds at 2.00 PM and 5.00 PM. Biochemical and endocrines parameters, blood gases and electrolytes were analysed during the 2nd, 32nd and 60th day of the study. Alterations in physiological parameters were more significant in Malabari goats. However, a negative correlation was observed between in-house relative humidity and all physiological parameters during all the different times. Behavioural patterns were influenced by increased IT and THI and the breeds spent more time in standing position during heat stress. A significant difference was observed within the study period in the pO2, Na+, HCO3- and blood pH. A significant difference was observed between the breeds for K+, Cl- and HCO3- levels. A significantly higher glucose level on the 32nd day and a lower total cholesterol level in the latter half of the experimental period were noticed in Malabari and crossbred. Mean total protein levels of all the breeds were significantly increased on the 32nd day. Increased GGT levels were observed in the first half of the experimental period in all breeds. Higher cortisol levels in Malabari and crossbred could be estimated in the first half of the experiment. Although Malabari showed higher T3 levels on the 32nd day compared to other breeds, within the breeds no significant difference in T3 levels could be noticed. However, significantly higher T4 values were recorded on the 32nd day and 60th day only in Crossbred breeds when the IT and THI were high. Thus it has been shown that heat stress was affecting the physiology, metabolism and behaviour of breeds. The increase in respiratory rate and rectal temperature were the first signs of heat stress in these breeds. The physiological manifestations of stress were the greatest for Malabari goats and the least for Attappady black.