Effects of relative humidity during incubation on hatchability and body weight of broiler chicks from young breeder flocks.

We conducted an experiment to determine the effect of relative humidity (RH) during incubation on characteristics of hatched chicks from eggs produced by young broiler breeders. Eggs were collected for 6 consecutive d, every other week, in each of two trials from broiler breeder flocks at 26, 28, and 30 wk of age. The eggs were randomly distributed in machines according to RH treatments that were 43, 53, and 63% RH from set to pulling time at 21.75 and 22 d of incubation for Trials 1 and 2, respectively. The same dry bulb temperature (37.5 C) was used throughout incubation for both trials. Body weight at hatch, but not BW at pull (removal from machine), increased significantly with increasing RH treatment. The BW at hatch and BW at pull increased with increasing hen age. Percentages of late dead and fertile hatchability were the highest for the 63% and 53% RH treatments, respectively. These data demonstrated that, although a high RH during incubation produced chicks with increased BW at hatch, this extra weight was greatly reduced by time of pull, which suggests a significant rate of evaporation even in the presence of high RH. Further, the high RH appears to have a detrimental effect on embryonic development, as evidenced by the increased percentage of late dead.