Heat stress is a situation where too much heat is absorbed by a person, a plant or an animal and causes stress, illness or even death. Therefore, the objective of this review was to compile current knowledge and evidence from literature about the effects of heat stress in poultry production, and productivities. Heat stress is manifested by elevated body temperature, hot, dry skin, lack of sweating and neurological symptoms such as paralysis, headache, vertigo and unconsciousness. Poultry seems to be particularly sensitive to temperature-associated environmental challenges, especially heat stress. In the first days of their life poultry need hot climate (32-38°C), but the optimal temperature decreases rapidly with age by 2.5-3.0°C per week. Birds may use sand baths to dissipate the heat from the body, move to a shaded area or seek a micro-environment that avoids extremely high environmental temperature. Birds rose in an open-sided house at 37°C and humidity level of 50-60% showed signs of panting and wing lifting, elevation of body temperature, lower feed consumption, a higher feed conversion ratio, and lowered body weight gain. In females, heat stress can disrupt the normal status of reproductive hormones at the hypothalamus and ovary leading to reduced systemic levels and functions. Also in males, semen volume, sperm concentration, number of live sperm cells and motility decrease when subjected to heat stress. In egg production, heat stress has a significant harmful impact on body weight, and feed consumption of laying hens at peak production, egg weight, shell weight, shell thickness, and gravity. Both meat type and egg laying chickens respond negatively to high ambient temperatures. Heat stress reduces the relative weights of lymphoid organs like spleen, thymus and cloacae bursa.
The relationships of body temperature to weight gain, feed consumption, and feed utilization in broilers under heat stress