Posthatch incubation time and early growth of broiler chickens.

Fertile eggs from broiler breeder hens were hatched to evaluate the effects of time of hatch and time held in the incubator posthatch on subsequent chick weights to 4 weeks of age. All chicks suitable for removal at 486, 492, 498, 504, 510, 516, and 522 hr of incubation in Trial 1 were weighed at their respective hatch times. One-half of each group remained in the incubator until 522 hr and the rest were placed in brooding pens at the initial weighing time, with water provided immediately and feed 6 hr later. The earlier the chicks hatched, the greater was the weight loss when held in the incubator to 522 hr (over 10% loss for those hatched at 486 and 492 hr). Males removed at hatch times of 486, 492, 498, and 504 hr were significantly heavier to 4 weeks of age than were their hatch mates held to 522 hr. A similar but less pronounced response was noted for females. Time on feed did not account for the total differences noted. Earlier hatching female chicks in Trial 1 were heavier at the time of hatch. They tended to maintain this weight advantage to 4 weeks of age when not held, but lost it when left in the incubator for the total hatching period. This effect was less pronounced for males. Trial 2 eggs were obtained from a different breeding source that had a larger egg size. Resulting chick weights were a higher percentage of initial egg weight than those in Trial 1. With hatch times of 492, 500, 508, and 516 hr, the trend was similar to that in Trial 1 but much less pronounced.