Effects of dietary protein level and age at photo stimulation on reproduction in broiler breeders

An experiment was conducted to study the effects of dietary crude protein (CP) levels during lay and age at photo stimulation (PS) on reproduction traits in broiler breeders females. The study consisted of a 2×2 factorial arrangement of treatments, with 2 dietary CP levels (high CP = CPh or low CP = CPl) and 2 ages of PS (early age (21 wk) = PSe or late age (23 wk) = PSl). Diets were iso-caloric (2,800 kcal/kg AMEn) and calculated CP content of the low CP diets was 1.5% lower during all phases. In total 480 females and 64 males between 20 and 60 weeks old were studied. Total egg production was similar between birds fed the CPl and CPhl diets during phases 1 (20 to 34 weeks) and 2 (35 to 46 weeks). For the overall laying period (20 to 60 weeks) birds fed the CPl diet tended to produce 4.7 less total eggs compared to the CPh diet, which was mainly caused by 2.8 less total eggs during the 3rd phase. Hatchability of set eggs tended to be lower for the birds fed the CPl diet which resulted in a lower number of chicks during the 3rd phase but not during phases 1 and 2. The PSe birds produced, during the 1st phase, 2.5 and 2.6 more total and settable eggs, respectively, however this disappeared during the rest of the laying period. During the 1st phase a higher fertility and a tendency to a higher hatchability of set eggs was found for the PSe birds. Chick weight in the 1st phase was highest for PSe birds which resulted in a tendency to a higher overall chick weight. Chick production in the 1st phase was increased for the PSe birds resulting in a tendency to higher overall chick production of almost 8 chicks. It was concluded, that egg and chick production during the 1st and 2nd phase was not affected by dietary CP level, however, egg and chick production during the 3rd phase was reduced for the CPl birds. On the other hand, PSe birds showed an increased number of chicks with no major effects on incubation traits.