| Abstrakt: |
This paper reviews adverse effects of heat stress on haematology and small intestinal changes as well as the beneficial effects of antioxidant agents, and probable mechanisms by which the agents ameliorate heat stress. High ambient temperature and high relative humidity cause heat stress, which negatively impacts on production, reproduction, immunity and health of broiler chickens. The cardiovascular system, particularly sensitive to changes in temperature, is an indicator of physiological responses to stressors by broiler chickens. Heat stress decreases small intestinal blood flow, erythrocyte count and haemoglobin concentration and alters the ratio of leucocyte types. Impaired blood flow causes injury to small intestinal morphology, including villi and crypts; impairs digestion, decreases rate of nutrient absorption and bird development, resulting in reduced body weight in broiler chickens. Antioxidant supplementation, involving vitamins C and E, fisetin, betaine, probiotic, taurine and melatonin, boosts the capacity of biological antioxidant barrier to combat reactive oxygen species, which are generated in excess during heat stress. In conclusion, antioxidants, by ameliorating adverse effects of heat stress on haematological and small intestinal changes, are promising prophylactic agents in enhancing productivity of broiler chickens under heat-stress conditions. [ABSTRACT FROM AUTHOR] |
