Strategies to Enhance Broiler Meat Production During Summer Heat Stress

Broiler meat is generally considered to be an economical source ofmeat protein for the average consumer in many areas of the world. In order for this product to maintain its competitive edge, production volume and efficiency of production in less developed countries must be improved. One factor which generally disrupts production in certain geographical areas is heat stress. The adverse effect ofheat stress on production is primarily due to decreased weight gain and increased mortality. This paper reviews four studies conducted to assess the effects of high environmental temperature on broiler growth and meat yield as well as to evaluate the impact of dietary mineral additives on performance. In the first experiment, commercial broilers were reared from 22 to 49 days ofage at either 23.9 constant temperature (thermoneutral, TN) or 23.90C to 35°C cycling high temperature (heat stress, lIS). Birds grown in the HS environment weighed 21% less (P <.015) than those raised under TN conditions. Whole carcass weight and carcass part weight from TN birds were greater than from ns birds. In the second experiment, birds reared under HS received potassium chloride (KCI) in the drinking water either continuously; during the hot portion of the daily heat cycle only, or were not allowed to consume KCl. Birds receiving KCl continuously gained 7% more weight (p < .05) than the untreated controls. In the third experiment, liS broilers were provided either no water additive, KCI, or sodium chloride (NaCl) in the drinking water. Administration of NaCI resulted in increased gain (P < .05) relative to controls receiving no electrolytes, In the fourth experiment, the relative biological availabilities ofmanganese from Mn proteinate, MnS04 and No were compared under TN and HS growth environments. Based on ratios of slopes from multiple regression analysis of bone Noon Nointake from different sources, the biological availabilities ofNoProteinate and No relative to MnS04 (100%) were 125 and 83% respectively in TN birds and 145 and 82% respectively in HS birds.