Ontogeny of deep-body cold sensitivity in Pekin ducklings Anas platyrhynchos

Abstract

The ontogeny of deep-body cold sensitivity was studied in 1 to 12 days old Pekin ducklings Anas platyrhynchos. Deep-body cold sensitivity was deter- mined by means of thermodes implanted in the abdo- minal cavity. The thermodes were perfused with cold water for 15-min periods to lower the core temperature. Cooling of the body core elicited increases in metabolic rate and vasoconstrictions in the legs of all the duck- lings. From the changes induced in metabolic rate and core temperature, deep-body cold sensitivity values of between ˇ5:17 and ˇ6:36 W AEkg )1 AE ∞C )1 , were esti- mated. These values, which are in the range of those reported previously for adult Pekin ducks, did not change with age, and it is concluded that deep-body cold sensitivity is fully developed at hatching. Our next aim was to investigate whether the autonomic responses elicited by exposure of ducklings to cold ambient con- ditions could be explained by temperature changes within the body core. During cold exposure, the increase in metabolic rate was not accompanied by a concomi- tant decrease in core temperature. On the contrary, deep-body temperature increased slightly during the initial phase of cold exposure. The ducklings attained a metabolic rate amounting to 85-90% of their peak metabolic rate before the core temperature fell below the regulated level measured at thermoneutrality. Thus, despite the findings that Pekin ducklings have a highly- developed deep-body cold sensitivity, their metabolic cold defence under natural conditions seems to be me- diated primarily by peripheral thermoreceptors.