Fasting and diet affect the tolerance of young chickens exposed to acute heat stress.

The interaction of nutritional status on the tolerance of young chicks to acute heat stress (HS) was investigated. The results of experiment 1 demonstrated that fasting for 24, 48 or 72 hours progressively increased survival time (ST) of chicks exposed to HS. When compared to that of non-fasted (NF) chicks ST more than doubled for 48 and 72 hour fasted chicks. During HS plasma glucose increased in fasted chicks but decreased in NF chicks. Conversely, plasma free fatty acids decreased in fasted chicks and increased in NF chicks. Plasma phosphate of all chicks fell markedly as a result of HS. Chicks of experiment 2 were fed a "carbohydrate-free" diet (CF). Survival time of NF chicks fed CF was significantly greater than that of NF chicks fed a diet containing glucose. The apparent metabolic responses of NF chicks fed CF corresponded to those of fasted chicks of experiment 1. It was suggested that the metabolic substrate utilized by chicks during HS influences ST. The effect of CF diet on ST was also observed in chicks which were fasted for 48 hours prior to HS. Plasma phosphate of chicks exhibiting fasting metabolic responses was not significantly different at heat induced prostration despite marked differences in ST. The results of experiment 3 demonstrated that ST of fasted (24 hour) chicks previously fed a low phosphorus diet was markedly lower than compared to that of fasted chicks fed adequate dietary phosphorus. The effect of diet was found to be dependent on metabolic status since level of dietary phosphorus fed had no effect on ST of NF chicks. The results of the present study indicated that metabolic and nutritional status affect the tolerance of young chicks acutely exposed to high ambient temperature.