Effects of dietary protein level and age at photo stimulation on reproduction traits of broiler breeders and progeny performance

A study with a 2 x 2 factorial arrangement was conducted to determine the effects of 2 dietary crude protein levels, high (CPh) or low (CPl), supplemented with free amino acids (AA), and 2 ages at photo stimulation (PS)-early (21 wk; PSe) or late (23 wk; PSl)-on reproduction traits of broiler breeders and progeny performance. Diets were isocaloric, and calculated CP content of the CPl diets was 15 g/kg lower than the CPh diets during all phases. A total of 480 female and 64 male Ross 308 breeders of 20 wk of age were used. Total egg production was similar between CPl and CPh birds during phase 1 and 2 but was reduced by 2.8 eggs for CPl birds during phase 3. For the overall laying period, CPl birds tended (P = 0.075) to produce 4.7 fewer total eggs. Hatchability of set eggs was similar between CPl and CPh birds during phases 1 and 2 but tended (P = 0.064) to be lower for CPl birds in phase 3. PSe birds showed an advanced age at sexual maturity and age at peak production of 4.6 and 5.3 d, respectively, resulting in 2.5 more total eggs during phase 1. During phase 1, PSe birds showed an almost 5% increased fertility. Chick production in phase 1 was higher for PSe birds resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks. Progeny from early PS breeders showed an overall significant lower feed conversion ratio (FCR). It was concluded that egg and chick production during phases 1 and 2 were not affected by dietary CP level, but egg and chick production was reduced for CPl birds during phase 3. On the other hand, PSe birds showed an increased number of chicks. It is possible to decrease CP level of breeder diets with comparable reproduction from 22 to 46 wk; however, this is questionable for phase 3. For maximal chick production, early PS is recommended.