The effects of age, energy and protein intake on protein turnover and the expression of proteolysis-related genes in the broiler breeder hen.

A study was conducted to determine the changes that occur to proteolysis and related genes due to age, protein, and energy intake in high-yield broiler breeder hens (Gallus gallus). Cobb 700 broiler breeders were randomly assigned to one of six diets in a 2×3 factorial fashion. Two levels of energy (390 and 450 kcal/day) and three levels of protein (22, 24, and 26 g CP/day) were utilized. Protein turnover was determined in the left pectoralis at 22, 26, 31 and 44 weeks. Relative mRNA expression of calpain 2 (CAPN2), proteasome C2 subunit (PSMA1), and F box protein 32 (FBXO32) were determined via RT-PCR at 20, 25, and 44 weeks. Contrasts indicate fractional synthesis rate (FSR) and FBXO32 increase to a maximum at 25-26 weeks and a decrease thereafter. A significant drop in PSMA1 and FBXO32 was observed between 25 and 44 weeks and matched the decrease observed in FBR. No differences were detected in the levels of fractional synthesis and degradation, or the expression of CAPN2, PSMA1, and FBXO32, due to protein or energy intake. In summary, protein turnover was upregulated during the transition into sexual maturity and decreased thereafter. The observed changes in degradation appeared to be mediated by the ubiquitin-proteasome pathway.