Restraint increases afebrile body temperature but attenuates fever in Pekin ducks (Anas platyrhynchos)

Abstract

In mammals, procedures such as handling, restraint, or exposure to open spaces induces an increase in body temperature (Tb). The increase in temperature shares some characteristics with pyrogen-induced fever and so is often called “stress fever.” Birds also respond to acute handling with a stress fever, which may confound thermoregulatory studies that involve animal restraint. We have measured the Tb responses of Pekin ducks on days when they were restrained and compared them to days when the birds remained unrestrained. Restraint induced a 0.5°C increase in Tb that was sustained for the entire 8 h of restraint. To determine whether the restraint-induced increase in Tb is mediated by prostaglandins (PGs) we compared the Tb responses during restraint after intraperitoneal injection with saline to the responses during restraint after injection with diclofenac sodium (15 mg/kg). There was no difference in response, suggesting that restraint affects Tb by a PG-independent mechanism. We also compared the Tb response to intramuscular injection of lipopolysaccharide (LPS; 100 μg/kg), a bacterial pyrogen, when the ducks were restrained or unrestrained. Despite Tb being higher at the time of LPS injection when the ducks were restrained, the maximum temperature reached after LPS injection was higher, and the period that Tb remained elevated was longer when the ducks were unrestrained. We conclude that restraint should be considered as a potential confounder in thermoregulatory studies in birds and presumably other species too.