Effect of heat stress on the behavioral and physiological patterns of Small-tail Han sheep housed indoors

This study was conducted to investigate the effects of heat stress on the behavioral and physiological patterns in Small-tail Han sheep housed indoors in summer without climate control. Sixteen adult animals were allocated into two groups of eight animals, based on sex: one group of eight rams and one group of eight ewes. Temperature-humidity index (THI) was used to assess the degree of heat stress. All sheep were subjected to a 10-day pre-experimental period of habituation to the experimental feed and environment. Physiological parameters monitored were respiratory rate (RR), rectal temperature (RT), and heart rate (HR). Blood chemistry parameters were also recorded, including plasma minerals and blood metabolites, from jugular vein blood samples. Behavioral parameters were lying, standing, excreting, drinking, foraging, walking, and ruminating. The research findings showed that there were some significant differences of behavior (standing, P = 0.001; walking, P = 0.049; ruminating, P = 0.010), physiology (RR, P = 0.0001; HR, P = 0.002; RT, P = 0.03;) and plasma minerals and blood metabolites (sodium, P = 0.047; phosphorus, P = 0.002; T4, P = 0.041; cortisol, P = 0.0047; triglyceride, P = 0.009) between ram and ewe and that heat stress also significantly affected (P < 0.05) standing, lying, foraging and drinking behavior, all of the physiological parameters and some of the blood chemistry parameters (chlorides, sodium, phosphorus, total protein, tetraiodothyronine, cholesterol, triglyceride, creatinine, cortisol, and glucose). These results indicate that ewe has better high-temperature tolerance than ram, and heat stress can alter behavioral and physiological patterns in Small-tail Han sheep housed indoors. These changes may allow the sheep to adapt better to the ambient temperature.