Reproductive performance, growth rate and body composition of broiler breeder hens differing in body weight at 21 weeks of age

The effects of variation in body weight at 21 weeks of age on subsequent growth rate, body composition and reproductive performance were studied in broiler breeder hens from 22 to 62 weeks of age. Pullets were sorted into three groups on the basis of body weight (low, medium and high) at 21 weeks of age. Pullets of the low-weight group contained a greater percentage of carcass water and less carcass fat at 22 weeks of age than did the medium- and high-weight pullets, and less carcass protein than the high-weight birds. The relative difference in body weight between the three groups of hens was maintained to 62 weeks of age, the high-weight hens being heavier than the low- and medium-weight hens at the end of the study. The low-weight birds began to lay later than the medium- and high-weight pullets. The low- and medium-weight birds were lighter in weight compared to the high-weight pullets at sexual maturity. Total egg output was lower in the low-weight hens than in the medium- and high-weight hens. No difference was seen in sequence and intersequence pause parameters or in fertility, embryo viability or embryo production between the three groups of hens. On a percentage basis, there were no differences in body composition between groups of birds at 62 weeks of age. It was concluded that pullets which are underweight at 21 weeks of age exhibit a poorer production record than do pen-mates which are of normal or greater than normal body weight. Key words: Broiler breeder hens, egg production, body weight, body composition, sequence length, fertility, embryo viability