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. Experiment 1 demonstrated that fasting for 24, 48 or 72 h progressively increased survival time (ST) of chicks exposed to HS. Compared to that of non-fasted (NF) chicks ST more than doubled for 48 and 72 h fasted chicks. During HS plasma glucose increased in fasted chicks but decreased in NF chicks. 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. The metabolic substrate utilized by chicks during HS apparently influences ST. The effect of CF diet on ST was observed in chicks which fasted for 48 h prior to HS. Plasma phosphate of chicks exhibiting fasting metabolic responses was not significantly different at heat induced prostration despite marked differences in ST. Experiment 3 demonstrated that ST of fasted (24 h) chicks previously fed a low P diet was markedly lower when compared to that of fasted chicks fed adequate dietary P. The effect of diet was dependent on metabolic status since level of dietary P fed had no effect on ST on NF chicks. Metabolic and nutritional status apparently affect the tolerance of young chicks acutely exposed to high ambient temperature.