The effect of thermal manipulations during the development of the thyroid and adrenal axes on in-hatch and post-hatch thermoregulation

This study aimed to elucidate the effects of thermal manipulation (TM) during the development and maturation of the thyroid and adrenal axis on broiler chicks hatchability and thermoregulation during hatch, and to evaluate the improvement of thermotolerance acquisition of TM chicks by thermally challenging them post-hatch. Fertile Cobb eggs were divided into three treatments: control, 12 and 24 H. The control eggs were incubated under standard conditions, whereas the 12 and 24H eggs were incubated from 7 d of incubation (E7) until E16 (inclusive) at 39.5 degrees C and 65% RH for 12 h/d (12 H) or continuously (24 H). Hatchability, BW and quality of the hatched 24 H chicks were negatively affected, but exhibited significantly improved thermotolerance on heat stress at 3 and 10d of age for males and females, respectively. It can be concluded that continuous TM during embryogenesis impaired broiler chick performance, but improved their ability to thermoregulate in response to thermal challenge mainly by reducing heat production. (C) 2008 Elsevier Ltd. All rights reserved.