Deterioration effects of heat stress on farm animals performance in tropical and subtropical regions

The thermal comfort region for greatest animals is between 4 °C and 25 °C and when environmental temperature surpasses 25°C, animals suffer from heat stress conditions. Over 50% of the cattle population is located in the tropics and it has been appraised that heat causes severe economic loss in approximately 60% of the dairy farms around the world. In tropical and subtropical countries, the climatic characteristic is the major constraint on animal productivity. In severe heat stress, growth, milk yield, milk composition and reproductive traits are reduced as a result of the extreme changes in biological functions affected by heat stress. Heat stress disturbs the steady-state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage. Although heat stress causes a decline in dry matter intake, the cow's energy and protein requirements in hot environments increase. This review provides an overview of the impact of heat stress on farm animals.