Development of avian thermoregulatory system during the early postnatal period: development of the thermoregulatory set-point

The development of colonic temperature and of heat production in 1- to 10-d-old chicken, turkeys and Muscovy ducklings was investigated after short-term (l h) exposure in climatic chambers to ambient temperatures between 10 and 40°C. In additional experiments the development of colonic temperature and preferred ambient temperature was studied in a temperature gradient tunnel (ambient temperature range 10- 45 ° C). The decrease in biological optimum temperature (identical with the ambient temperature at which the organism is exposed to minimal thermal load) and in the preferred ambient temperature with increasing age indicated that the lower colonic temperature during the first days after hatching is caused by changes of the thermoregulatory set-point . Compared with normally incubated ducklings, an incubation temperature (34 .5 °C) lower than the usual 37 .5 °C during the last week of embryonic development may induce a lower thermoregulatory set-point. These birds have a higher postnatal cold tolerance, they prefer lower ambient temperatures and have a higher heat production at low ambient temperatures at the first day post-hatching