Role of HSP and Leptin in Dairy Animals during Thermal Stress: A Review

Thermal stress is a unique and complex process which alters the normal physiological mechanisms. Heat shock proteins (HSPs) are known to be highly conserved and ubiquitous proteins synthesized in response to several stimuli. The HSP inducers have been categorized as environmental (heat shock, UV radiation, heavy metals, amino acids, oxidative stress, etc.) pathological (bacterial or parasitic infections, fever, inflammation, etc.) and physiological (growth factors, cell differentiation, hormonal stimulation or tissue development, caloric restriction, etc.). The HSPs play an important role for maintaining cellular functioning under environmental challenges and protein denaturation conditions. There is a great potential for using HSP72 expression to detect natural adaptation and exposure to stress in natural populations. Leptin is a 16 kDa polypeptide hormone secreted primarily from the cells of white adipose tissue. Leptin acts through both central and peripheral mechanisms to affect feeding behaviour, lipid and glucose metabolism, thermogenesis, reproductive and endocrine functions. Leptin also plays an important role in the regulation of body weight and composition, e.g. reduction in feed intake and increase in energy expenditure. Bovine lymphocytes express Ob-Rb gene (leptin receptor) and also express leptin. There are ample information on the central role of leptin in brain and neural tissue regulation. In dairy cattle, the increase in milk yield has been associated with a negative energy balance and a decrease in fertility during early lactation. The hormone leptin is involved in regulation of nutritional status and reproductive function.