Phosphorus nutrition and fasting: interrelated factors which affect the survival of young chickens exposed to high ambient temperature.

The interaction of phosphorus nutrition and fasting on the tolerance of young chickens acutely exposed to high temperature was studied. We also investigated a possible relationship between plasma phosphate (Pi) and body temperature (Tr) of chicks during heat exposure. Survival time (ST) of 24-hour fasted (F-24) chicks previously fed a low-phosphorus diet (LP) was markedly lower than ST of F-24 chicks fed an adequate phosphorus diet (AP). Diet, however, had no effect on ST of chicks fasted 12 hours (F-12). The apparent metabolic responses of F-24 chicks were qualitatively different than those of F-12 chicks suggesting that the effect of previous phosphorus nutrition was dependent on metabolic status of chicks before heat exposure. The concentration of Pi during heat exposure of F-24 chicks fed the experimental diets was highly (P less than 0.001) correlated with Tr. At heat-induced exhaustion, Tr of chicks fed either diet was not different. Pi of these groups at this point was nearly identical despite marked differences in the time at which this event occurred. An investigation concerning a possible relationship between Pi and the respiratory failure known to occur in hyperthermic chickens, revealed that respiratory muscular fatigue is not the primal cause of respiratory failure. Our results demonstrated that phosphorus nutrition, Pi and metabolic status are dependent factors related to the tolerance of young chickens exposed to high temperature.