Specific regulation of muscle protein metabolism in broilers by dietary fermented cottonseed meal

This study aimed to investigate the regulatory effects of replacing soybean meal with varying proportions of fermented cottonseed meal in the diet on protein metabolism in the pectoral and leg muscles of white-feather broilers. The experiment was divided into two phases: early-growth (1-21 days) and late-growth (22-42 days) phases. The control group was fed a basal diet without fermented cottonseed meal (0%), whereas the experimental groups were fed soybean meal replaced with 3, 6, and 9% fermented cottonseed meal. The effect on protein metabolism was evaluated by measuring the expression of key genes in the IGF1/mTOR, AMPK, and UPP pathways in muscle tissue. During days 1-21, experimental groups showed significantly higher IGF-1 and mTOR mRNA expression in leg muscles compared to controls, while FoxO3 expression in pectoral muscles was reduced. The 3 and 6% groups had elevated IGF-1 and PI3K, and the 6% group showed higher AKT and mTOR in pectoral muscles and PI3K in leg muscles. TSC2 expression was suppressed in the 3 and 6% groups, while Atrogin-1 and MuRF1 were lowest in the 6% group. During days 22-42, the 3 and 9% groups had increased IGF-1 and mTOR in pectoral muscles, whereas the 6% group showed higher AKT and PI3K in leg muscles. FoxO3 was significantly downregulated in the 9% group. In summary, fermented cottonseed meal can regulate protein metabolism in the pectoral and leg muscles of Cobb broilers by enhancing the expression of genes related to the IGF-1/mTOR pathway and suppressing the transcription of certain key genes in the UPP, thereby promoting protein deposition, with an optimal supplementation level of 6%.