Heat Stress and Livestock Adaptation: Neuro-endocrine Regulation

Heat stress is the major intriguing factor influencing livestock production in the changing climatic condition. Therefore, research efforts are needed to identify thermotolerant breeds which can help to optimize livestock production during heat stress challenges. The heat tolerance in livestock is determined through various mechanisms and neuroendocrine regulation is one of the crucial pathways by which the animal survives the stressful condition. Hence, this paper is an attempt to elucidate the hidden intricacies of neuroendocrine mechanisms which helps the livestock to survive in a specific environment. The hypothalamic-pituitary-adrenal (HPA) axis plays a significant role in the release of several neurotransmitters and hormones which regulates the thermoregulatory mechanisms in animals. The corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and glucocorticoids are the primary products of HPA axis which ultimately controls the stress response pathways in animals. The HPA axis regulates the energy partitioning for supporting the life-sustaining activities through the process of hepatic gluconeogenesis. Epinephrine and norepinephrine levels are found to be increased in heat stressed animal. These neurotransmitters regulate the cardiovascular rate during heat stress and ensure supply of blood to vital organs. The thyrotropin-releasing hormone (TRH), thyroid stimulating hormone (TSH) and thyroid hormones (T3 and T4) are the components of metabolic pathway in regulating body heat production. Further, leptin secreted from adipocytes also considered being negatively influencing stress response. Further, aldosterone plays a pivotal role in electrolyte and fluid homeostasis and regulation of Na + and K+. The lactogenic hormone prolactin was found to be decreased while somatotropin hormone level was increased during heat stress reflecting negativity in milk production and growth. This indicates the complexity of the interaction between the neuroendocrine regulators to maintain homeostasis during heat stress in livestock. Generally, cortisol and thyroid hormones are considered to be important biological markers of neuroendocrine pathway regulation of adaptive mechanisms during heat stress in livestock.