Effect of heat stress in tropical livestock and different strategies for its amelioration

Stress is a broad term, generally used in negative connotation and is described as the cumulative detrimental effect of a variety of factors on the health and performance of animals. Heat stress occurs in animals when there is an imbalance between heat production within the body and its dissipation. Heat stress is one of the wide varieties of factors which causes oxidative stress in-vivo. Reactive oxygen species (ROS), the major culprits for causing oxidative stress, are constantly generated in vivo as an integral part of metabolism. ROS may cause oxidative stress when their level exceeds the threshold value. They trigger progressive destruction of polyunsaturated fatty acids (PUFA), ultimately leading to membrane destruction. Body employs antioxidants to quench these free radicals. The enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) act by scavenging both intracellular and extracellular superoxide radical and preventing lipid peroxidation of plasma membrane. Non-enzymatic antioxidants include vitamins like vitamins C, A and E, proteins like albumin, transferrin, glutathione (GSH) etc. Antioxidant nutrient supplementation especially vitamins C, A and E, zinc and chromium can be used to attenuate the negative effects of environmental stress.