Perinatal broiler physiology between hatching and chick collection in 2 hatching systems.

Little is known about physiological responses of early- versus late-hatching chicks to early posthatch conditions in broiler practice. We investigated effects of hatching time on perinatal broiler physiology in 2 hatching systems, differing in conditions: a conventional hatcher, where chicks are deprived of feed and water between hatching and the moment of chick pulling (d E21.5), and a patio system, in which the hatching and brooding phase are combined, and chicks have immediate posthatch feed and water access. Climate conditions in patio also differ with about 3°C lower temperature and 20% lower RH compared with conventional hatchers. At E18, fertile eggs were transferred to either a hatcher or the patio until the end of incubation. From each system, 50 newly hatched chicks were collected at 3 hatching times: at 468 h (early), 483 h (midterm), and 498 h (late) of incubation, of which 25 chicks were decapitated for analyses of physiological parameters. The other 25 chicks were returned to the hatching system for analyses after 515 h of incubation (E21.5). At hatch, weights of the heart, lungs, stomach, and intestine increased with hatching time, concurrent with a decrease in residual yolk weight, regardless of hatching system, and indicating that later hatching chicks are more matured. Weights of the heart, liver, stomach, and intestines were lower in hatcher than in patio chicks. Between hatch and E21.5, residual yolk weight decreased, whereas organ weights increased in both fasted hatcher and fed patio chicks, but at a higher rate in the latter. At E21.5, plasma glucose and triiodothyronine had increased with time after hatch in patio chicks, whereas levels were similar among hatching times and lower in hatcher chicks. Early feed and water access seems to enable early hatching chicks to compensate for their apparent disadvantage in development at hatching, whereas chicks subjected to fasting show metabolic adaptations to preserve nutrients. Chick physiology at chick pulling time was shown to vary with time after hatching and posthatch conditions, especially feed access.