Research Note: Do broiler breeder hens use hypothermia to cope with cold environments and feed restriction?

Abstract

The deep body temperature (T_b) of broiler breeder hens was measured in a pilot trial conducted as part of an experiment in which the response of the birds to dietary protein was evaluated at different cyclical air temperatures (T_a). Temperature data-loggers were implanted in the abdominal cavity of the birds. Most birds presented night T_b (T_bn) compatible with nocturnal, facultative hypothermia, a phenomenon not previously reported in broiler breeders. Hypothermia could not be related to level of dietary protein, feed intake, body weight, or change in body weight. It appeared in birds subjected to nocturnal T_a (T_an) ~10 °C but not at T_an of 20 °C, except in poor egg producers, which were normothermic when exposed to T_an= 10 °C. Sensors were calibrated and data corrected with calibration factors, overruling the possibility of sensor failure. Some of the sensors became embedded in the abdominal fat pad; considering that the area of surgical incision was defeathered, a possible reduction of the temperature of the abdominal wall could be the reason for the unusual T_b measurements. Nevertheless, this would not explain the occurrence of normothermia in birds kept at T_a = 20 °C, a value much lower than T_b. Unfortunately, no significant conclusions could be drawn from this experiment due to the reduced number of replications. Currently, additional experiments are being conducted to verify the occurrence of nocturnal, facultative hypothermia. Should the occurrence of nocturnal, facultative hypothermia be real, it will affect the way in which the circadian rhythms of T_b in broiler breeders are modelled.