Simulated natural lighting and constant 14-hour photoperiods

Spring-hatched broiler breeders housed in non-lightproof facilities are frequently maintained on long daylengths to prevent precocity, but controlled-feeding and delayed dissipation of photorefractoriness retard sexual maturation. Trials were conducted to determine the appropriate growth for birds maintained on 14-h photoperiods, and to compare responses with naturally increasing and decreasing daylengths. Birds maintained on 14-h photoperiods matured about 5 d earlier and produced 2 more eggs to 60 weeks for each 10-d advance in age at 2.1 kg. However, despite requiring 0.2 kg less feed to reach 2.1 kg, accelerating growth resulted in 0.5 kg more feed being consumed to sexual maturity. The accelerated-growth birds produced more eggs that were too small for hatching and more double-yolked eggs during the early weeks of production. The data suggest that profitability is maximised when constant-14-h birds reach 2.1 kg at about 18-19 weeks. There were no significant differences in maturity between conventionally-grown birds given increasing or decreasing daylengths or those held on 14-h photoperiods, though there was a tendency for the constant 14-h birds to have later maturity, to produce 6-7 fewer eggs to 60 weeks, and to consume more feed per egg, resulting in a lower economic margin than naturally lighted birds. The wisdom of rearing Springhatched broiler breeders on long photoperiods to avoid precocity is therefore questionable. Birds allowed faster growth, generally matured about three weeks earlier than conventionally-grown birds, but matured five weeks earlier when given an increasing lighting regimen that started from 10 h rather than 11 h. _______________________________________________________________________________________