Responses of two strains of female broiler breeders to a midcycle increase in photoperiod.

The influences of strain and a midcycle increase in photoperiod on the reproductive performance of broiler breeder hens were evaluated. At 22 wk of age, Strain X and Y pullets were randomly assigned to one of five groups [processed at 22 wk of age (A), processed after third oviposition (B), processed at 32 wk of age (C-32), processed at 40 wk of age (C40), and processed at 54 wk of age (C-54)] and were placed into individual laying cages. These groups were euthanized at different ages to analyze reproductive and carcass parameters. Photostimulation occurred at 22 wk of age when the photoperiod was increased from 8L:16D to 14L:10D. A light-tight wall partitioned the room into two halves. At 33 wk of age, half of the birds received an increase in photoperiod to 18L:6D, whereas the other half remained at 14L:10D. Body weight and abdominal fat pad weight increased with age. The number of large yellow follicles (LYF) decreased from 8.78 at sexual maturity to 4.60 at 54 wk of age. The number of atretic white follicles (WF) and small yellow follicles (SYF) also increased with age. Although there were no differences in BW, Strain Y had a greater egg weight throughout the laying cycle than Strain X. Peak hen-day egg production was 93.0%, and, overall, egg production was not affected by strain. Reproductive performance and ovarian morphology were not affected by the increase in photoperiod, presumably because peak egg production was so high. Carcass data demonstrated that frame size was determined by sexual maturity, whereas organ weights changed in response to reproductive status.