Assessment of Heat Stress in Dairy Animals under Field and Farm Conditions

摘要

Heat stress has adverse effects on growth, milk production and reproduction of dairy animals (Hansen, 2007). The problem of heat stress is growing day by day because of changes in the global climate. Heat stress is more common in the dry humid season, especially when the environmental temperature and relative humidity are high with prolonged exposure to direct sunlight. Stress is reaction of body to stimuli that disturb homeostasis and adversely affects the animal body system. To cope up with the adverse ambient conditions, animal body shows many neuroendocrine responses which may alter the physiological and biochemical reactions to acclimatize to its surrounding. The physiological responses and body temperature are inter-correlated. A rise of temperature accelerates biochemical reactions, and a lowering of temperature depresses these reactions, likewise appropriate physiological responses is exhibited. The fluctuations in physiological responses are directly correlated with the fluctuation in environmental temperature surrounding the animal. This physiological response or adjustment to change in external environment has effect on productivity of domestic animals. Mammals have developed a thermoregulatory mechanism whereby body temperature is maintained at a relatively constant level regardless of the temperature of the surroundings. Mammals are homeotherms which have optimal temperature zones or thermo-neutral zones for growth, production and reproduction within which animal's body temperature remains relatively constant (Farooq et al, 2010). However, long term exposure of animal to the atmospheric temperature above the thermoneutral zone alters the physiological functions of animal and animal may be called as heat stressed. Environmental heat stress is the most detrimental to dairy animals and results in the hindrance of feed consumption, decreased growth, milk production, and reproductive performance.