Meta-analysis of some physiologic, metabolic and oxidative responses of sheep exposed to environmental heat stress

A meta-analysis was performed from 66 references retained from a total of 147 ones. The aim was to study the relationship between the THI and some physiologic, metabolic and oxidative responses in sheep. The effects of the breed, physiological state and heat relieving strategies were investigated as well. PCA, GLM, one nested ANOVA and global correlations were used to assess the fixed effects. Respiration rate, rectal temperature and heart pulse vary significantly in response to THI increase. However, the magnitude of this variance is defined by the breed and the physiological state of the animal. Moreover, Mechanical heat relieving strategies allowed alleviating the drastic effects of hyperthermia on sheep physiologic responses, whereas some nutritional heat abatement strategies increased metabolic heat load and respiration rate. Antioxidant and mineral supplementations were able to protect animals from heat stress. Environmental-induced hyperthermia reduced feed intake, body weight, circulating glucose and cholesterol levels, and increased lipid and protein catabolism. Significant increase of cortisol hormone was recorded. Indeed, ambient- induced hyperthermia resulted in oxidative stress marked by a decrease of Se contents, enhanced SOD activity, high oxidative stress index, increased protein oxidation, reactive oxygen species production and MDA levels. We report here for the first time that respiration is a second source of free radicals generation in sheep under environmental-induced heat stress. Heat stress disturbs rectal temperature, respiration and heart rates, exacerbates the post absorptive metabolism as well as the antioxidant status of sheep. Therefore, animals increase their maintenance requirements at the expense of production needs, which become not priorities at all.