Length of incubation and hatchling body weight in quail selected for reduced or exaggerated adrenocortical responsiveness to brief restraint.

1. While changes in corticosterone (B) during late embryogenesis are thought to play a role in the hatching process, only a scant and controversial literature exists concerning the effects of in ovo B on the length of incubation and chick body weight at hatching. Because female Japanese quail selected for exaggerated (high stress, HS) rather than reduced (low stress, LS) plasma B response to brief mechanical restraint deposit more B into their eggs, these stress lines provide an excellent model to study the relationship between embryonic B and incubation length and hatchling body weight. 2. Differences in the duration of incubation and chick body weight at emergence were assessed using eggs laid by LS and HS quail. 3. On average, eggs from HS hens hatched 3.7 h sooner than did eggs from LS hens while mean body weight at emergence was similar in hatchlings of both lines. Thus, selection for exaggerated adrenocortical responsiveness is associated with a reduction in the length of egg incubation without altering hatchling body weight. 4. This finding is important to the poultry industry because it warns layer, breeder farm and hatchery managers that unless stress in hens during egg formation is avoided, an abbreviated incubation period may result.