ACCLIMATORY RESPONSES ACCORDED BY HEAT STRESS IN FARM ANIMALS: A REVIEW

Abstract

Globally, the climate is changing and this poses a threat to the survival and productivity of farm animals. One of the most important and critical consequences of climate change is increasing surface temperature all over the world resulting from increasing amount of greenhouse gases (water vapour, carbon dioxide, Nitrous oxide, Methane and ozone) concentration in the atmosphere. This elevates concentration of greenhouse gases in the atmosphere leads to an increase in the ambient temperature which is a contributing factor to heat stress in farm animals. Heat stress is any combination of environmental factors that causes the effective body temperature of the animal to be higher than the thermo neutral zone of the animal. Heat stress occurs when the core body temperature of a normal activity resulting from a total heat load (internal production and environment) exceeding the capacity for heat dissipation. This prompts behavioural, physiological, neuroendocrine and behavioural responses to reduce the stress. Behavioural responses of farm animals include increased water intake, reduced feed intake, increased standing and reduced lying behaviour. Physiological responses of farm animals to heat stress include increase in heat rate, respiration, rectal temperature, pulse rate, sweating rate, body temperature and reduction in rumination time in ruminants. Neuroendocrine responses of farm animals to heat stress is coordinated by the functioning of three neuroendocrine axis; the hypothalamic - pituitary – adrenal axis, hypothalamic - pituitary – thyroid axis and sympathetic – adrenal medullary axis. Metabolic responses of farm animals involve a reduction in the secretion and activity of thyroid hormones as regulated by the hypothalamic-pituitary-thyroid axis. Climate change is seen as a formidable challenge for farm animal production. Therefore, to achieve an optimum return from the livestock sector, understanding in depth, the various acclamatory responses of farm animals is necessary