THE EFFECTS OF THERMAL ENVIRONMENT ON THE GROWTH OF NEONATAL CHICKS .1. THE DEVELOPMENT OF THERMOREGULATION

A total of 150 1-day-old Hisex male chicks were used to investigate th e development of thermoregulation of neonatal chicks. The birds were e xposed to four thermal environments: 27 degrees C and 35 % RH, 27 degr ees C and 85 % RH, 35 degrees C and 35 % RH, and 35 degrees C and 85 % RH. The rectal and skin temperature were determined. The rectal tempe rature was increased by high ambient temperature or high humidity. The re was significant interaction between temperature and humidity; the h armful effect of high temperature on rectal temperature was aggravated by high humidity. Under low temperature (27 degrees C), the humidity had no significant effect on the rectal temperature. During the first day of exposure to 27 degrees C, the rectal temperature of chicks had a tendency to be decreased, but in the subsequent days it was not affe cted by low temperature. Temperature, humidity and their interaction a ll had a significant effect on skin temperature. The skin temperature was increased by low temperature (27 degrees C) and this increment was enhanced by high humidity. In the high temperature-low humidity envir onment, the skin temperature was also elevated, but it was decreased b y high humidity. It is suggested that. the thermoregulation mechanism of neonatal chicks is not weil developed; they were more sensitive to high temperature than low temperature. When the neonatal chicks were e xposed to high temperature, the birds could nor make a proper adjustme nt in feed intake within the first 48 h of heat exposure.