Heritability of body surface temperature measured by infra-red thermography in laying hens exposed to high temperature conditions

Improving the adaptation of poultry to heat stress by selection requires having measures that are easy to obtain and that are heritable. Internal body temperature is used to quantify heat stress but is long to obtain and lacks precision. We tested the possibility of infrared thermography to record body temperature (BT) in two commercial lines of laying hens between 28 and 72 wk, submitted cyclically to periods at neutral or high ambient temperatures (19.6°C and 28.4°C, resp.). Mean BT were estimated for the wing, comb and shank areas (N=4465-4481 in line A, 7279-7311 in line B, depending on the trait). During hot periods, mean BT increased by 29.5-32.6% on the wing, by 20.6-22.5% on the shank and by 28.9-29.8% on the comb. Heritability of the mean BT was estimated in both lines. It was very low for the wing (0.03) consistently with the fact that wing BT is mainly linked to environmental temperature and to feather coverage. Heritability of the shank and the comb BT was also low but significantly different from zero (0.08-0.14), which indicates that the capacity of animals to dissipate heat is partly under genetic control. Heritability of the shank BT was the most consistent between the two lines, probably reflecting a higher precision of the measure of this part, the easiest to distinguish from environment. Using infrared thermography in chicken experimentation seems promising but a higher degree of precision is required in order to increase the heritability of these traits.