To what extent can the age at sexual maturity of broiler breeders be reduced

Two trials were conducted to investigate the effects of growth manipulation and early photostimulation on age at sexual maturity and, in one trial, subsequent laying performance, in broiler breeders. In the first trial, the possibility of reducing the age at sexual maturity, using early photostimulation and increasing the growth rate to achieve 2100 g at 15 weeks, was assessed. Sexual maturity was advanced by 15 d and the total number of eggs laid to 60 weeks, on a hen.week basis, was reduced significantly, by six. Mean egg weight was unaffected, but the number of unsettable eggs was increased by 2.6. Using 12 h rather than 16-h daylengths during the laying period resulted in a significant increase (7) in number of eggs laid. In the second trial, birds were transferred from 8 to 16-h daylengths at 10, 11, 12, 14, 16 or 18 weeks to determine the age at which they were able to dissipate photorefractoriness, and become photosensitive. Short-day controls were maintained on 8-h daylengths throughout. Birds were grown to achieve 2100 g at either 15 or 20 weeks. No interaction occurred between age at photostimulation and body weight. Because broiler breeders exhibit photorefractoriness, the earliest age at which the pullets responded to photostimulation was 14 weeks, so no advantage would be gained in terms of advancing sexual maturity by photostimulating earlier than this age. However, whilst some further advance in sexual maturity may be achieved by rearing the birds on a faster growth curve this would only be profitable through the advantages of being able to use one rearing unit to service three, instead of two, laying farms.