Thermal conditioning during layer chick embryogenesis

Thermal conditioning during embryonic development has demonstrated to be important for the acquisition of thermo-tolerance in broiler chickens. However, little is known about the effects in laying hens. In the current study, laying hen embryos were conditioned at d 14-18 of incubation by exposure to 40oC egg shell temperature (EST) for 4 h/day (n=96). Control embryos (n=96) were incubated at 37.8oC EST throughout incubation. After hatch, chicks from each treatment were divided into 3 subgroups (n=32 per group) and subjected to a heat challenge at d 2 (40oC), d 8 (40oC) or d 34 (35oC). One day prior to the heat challenge, the preferred ambient temperature of the chicks was determined with a temperature preference test. Blood samples were taken before and after the heat challenge at d 34 to investigate plasma T3, T4 and corticosterone levels. Thermal conditioning decreased the incubation time with 7 h (p