Chicken hatchlings prefer ambient temperatures lower than their thermoneutral zone

Abstract

We investigated whether or not the preferred ambient temperature (Tapref) of the 1-day old chicken hatchling, a precocial neonate with excellent locomotory capacity, clearly identifiable thermogenesis and independence from maternal care, coincides with the lower critical temperature (LCT) of thermoneutrality and minimal oxygen consumption ((V) over dot(O2)). Tapref of single chicks measured in a thermocline (N = 16) averaged 33.5 +/- 0.3 degrees C (mode, 33.3 +/- 0.4 degrees C). The same value was obtained in hatchlings studied in pairs. LCT was computed from the ambient temperature (Ta)-(V) over dot(O2) relationship, constructed by slowly decreasing the Ta of a respirometer from 38 to 29 degrees C over 2.5 h, while continuously measuring (V) over dot(O2) by an open-flow methodology; LCT averaged 36.4 degrees C +/- 0.3 or 36.8 degrees C +/- 0.4, depending on the method of computation. In all hatchlings Tapref was lower than LCT (P < 0.001), by a magnitude that depended on the method of computation of the two variables, 2.8 degrees C +/- 0.3 (P < 0.001) or 3.9 degrees C +/- 0.5. The Tapref-LCT difference implied that, at Tapref, (V) over dot(O2) was higher than at thermoneutrality. We conclude that in the chicken hatchling thermal preference does not coincide with thermoneutrality, probably because during development what seems optimal from a thermoregulatory viewpoint may not necessarily be so for other regulatory functions. (C) 2014 Elsevier Inc All rights reserved.