Effects of incubational humidity and hen age on embryo composition in broiler hatching eggs from young breeders

There is a paucity of information regarding the influence of incubational h umidity on the characteristics of broiler embryos from young hens that ofte n produce chicks of marginal quality. Therefore, the effects of broiler bre eder age (26, 28, and 30 wk) in young broiler breeders and incubator humidi ty (43, 53, and 63% RH) on embryonic growth between 16 and 21 d of incubati on, hatching chick weight, and embryo and chick body compositions were eval uated. Hatching broiler chick BW at 21 d was lower for 26-wk-old breeders c ompared to those at 28 and 30 wk, and the lowest RH decreased relative wet embryo weight. Embryonic growth, on wet and DM bases, was increased in eggs from the youngest hens. Embryo moisture content (EM) was lower at 16, 17, and 19 d of incubation in eggs from breeders at 26 wk when compared to thos e at 28 wk of age. The effects of RH on embryo crude protein and fat compos ition were not consistent and varied with breeder age and length of incubat ion. It was demonstrated that broiler breeder age affects embryogenesis and hatching chick BW. Furthermore, EM was influenced by breeder age, and chan ges in incubational RH between 43 and 63% affected embryogenesis without ha ving associated effects on EM or consistent effects on embryo crude fat and protein content. Nevertheless, a depression in embryogenesis with a reduct ion in incubational RH to 43% may accentuate poor posthatch performance of chicks from young breeders.