The interaction of phosphorus nutrition and fasting on the survival time of young chickens acutely exposed to high temperature.

Phosphorus nutrition and fasting are dependent factors which markedly influence the tolerance of young chickens to high temperature. A study was conducted to further characterize the nature of this interaction. Male chicks fed low phosphorus diets and fasted 24 hr exhibited significantly shorter survival time after exposure to acute heat when compared to fasted chicks previously fed adequate dietary phosphorus. When chicks were fasted for 48 hr, the effect of previous diet was considerably more pronounced. These results showed that the effect of low phosphorus nutrition was potentiated by fasting 48 hr which in itself improved survival time over that of chicks fasted 24 hr. The apparent metabolic responses of chicks to heat as indicated by changes in plasma glucose and total ketones were not related to the observed dietary effects. Plasma phosphate (Pi) and calcium (Ca) decreased significantly during heat exposure. The Ca/pi molar ratio was increased significantly at heat induced exhaustion, indicating a relatively greater heat induced change in Pi. From the initiation of heat exposure to heat exhaustion, the percent change in Pi, but not Ca, was similar in all groups despite marked differences in the time within which this occurred. We concluded that the effect of low phosphorus nutrition on heat tolerance of young chickens persists after a 48-hr fast. In addition, the effects of previous diet were somewhat more pronounced in 48-hr fasted chicks when compared to those fasted 24 hr.