ONTOGENY OF DEEP-BODY COLD SENSITIVITY IN PEKIN DUCKLINGS ANAS-PLATYRHYNCHOS

The ontogeny of deep-body cold sensitivity was studied in 1 to 12 days old Pekin ducklings Anas platyrhynchos. Deep-body cold sensitivity wa s determined by means of thermodes implanted in the abdominal cavity. The thermodes were perfused with cold water for 15-min periods to lowe r the core temperature. Cooling of the body core elicited increases in metabolic rate and vasoconstrictions in the legs of all the ducklings . From the changes induced in metabolic rate and core temperature, dee p-body cold sensitivity values of between -5.17 and -6.36 W . kg(-1).d egrees C-1, were estimated. These values, which are in the range of th ose reported previously for adult Pekin ducks, did not change with age , and it is concluded that deep-body cold sensitivity is fully develop ed at hatching. Our next aim was to investigate whether the autonomic responses elicited by exposure of ducklings to cold ambient conditions could be explained by temperature changes within the body core. Durin g cold exposure, the increase in metabolic rate was not accompanied by a concomitant decrease in core temperature. On the contrary, deep-bod y temperature increased slightly during the initial phase of cold expo sure. The ducklings attained a metabolic rate amounting to 85-90% of t heir peak metabolic rate before the core temperature fell below the re gulated level measured at thermoneutrality. Thus, despite the findings that Pekin ducklings have a highly-developed deep-body cold sensitivi ty, their metabolic cold defence under natural conditions seems to be mediated primarily by peripheral thermoreceptors.