Heat prostration of broilers as influenced by dietary energy source.

Abstract Three trials were conducted to study the effect of dietary energy source on mortality due to heat prostration in 8-week-old male broilers. The two isocaloric diets contained 1.00 or 7.00 percent added animal fat and were fed ad libitum for the 4- to 8-week experimental period. At 8 weeks of age, the dry-bulb temperature was increased from 21.1° C. with a dewpoint temperature of 10.0° C. to 40.6° C. over a 6-hour period, with a dewpoint temperature of 23.9° C. The temperature was held at 40.6° C. for 2 hours, then decreased to 26.7° C. over a 30-minute period. Mortality due to heat prostration was recorded at 30-minute intervals during the stress test. The results obtained indicate that the quantity of energy provided by fat compared to carbohydrate has an effect on mortality during the early stages of heat stress. Higher mortality due to heat prostration occurred in the birds receiving the diet containing the higher level of fat during the first three 30-minute intervals. During subsequent 30-minute intervals, there were no significant differences in mortality due to dietary treatment. The reason for the higher mortality in the birds receiving the diet containing the higher level of fat is not known. When the summer temperature approaches 38° C., mortality due to heat prostration is a problem. Economic losses due to heat prostration are especially large because they usually occur shortly before the broilers are marketable. Field reports indicate that male broilers are more susceptible to heat prostration than the females.