Breathing pattern and ventilatory chemosensitivity of the 1-day old Muscovy duck (Cairina moschata) in relation to its metabolic demands

Abstract

Adult birds have a ventilatory equivalent (pulmonary ventilation–oxygen consumption ratio, V˙ E/ V˙O2) lower than mammals because of the superior gas exchange efficiency of their respiratory apparatus. In particular, adult Muscovy ducks (Cairina moschata) have been reported to have an extraordinary low ventilatory equivalent (~14mL STPD·mL BTPS−1). We asked if similar high efficiency was already apparent in duck hatchlings. Breathing pattern and V˙E were measured by the barometric technique and V˙O2 by an open-flow methodology in 1-day old Muscovy duck hatchlings (N=21); same measurements were performed on chicken hatchlings (N=21) for purpose of comparison. During air breathing V˙E/V˙O2 was slightly, yet significantly, lower in ducklings (20.8) than in chicks (25.3), mostly because of a lower breathing frequency (f). The hatchlings of both species (N=14 per group) responded to inspired hypoxia (15 or 10% O2) or hypercapnia (2 or 4% CO2) with a clear hyperventilation; however, in ducklings the hypercapnic hyperventilation was smaller than in chicks because of a smaller increase in tidal volume and lower f. We conclude that duck and chicken hatchlings just a few hours old have the high ventilatory efficiency typical of birds, although possibly not as high as their adults. The low f and blunted V˙E response to hypercapnia of the newborn duck could be related to the aquatic habitat of the species. In such a case, it would mean that these characteristics are genetic traits, the phenotypic expression of which does not require diving experience.