Sex-dependent responses to posthatch protein-reduced feeding in broilers derived from low-protein-fed hens

This study evaluated the sex-dependent responses of broiler offspring derived from low-protein-fed hens to posthatch low-protein feeding, with emphasis on growth efficiency, carcass traits, amino acid metabolism, breast meat quality, and breast muscle transcriptomic profiles. A total of 312 broiler offspring were assigned to a 2 × 2 factorial arrangement with 2 posthatch dietary protein levels and 2 sexes and reared to 84 d. The low-protein diet represented a practical protein-reduced formulation in which Lys, Met, Thr, and Trp were supplemented, whereas Arg, Leu, Ile, and Val were not fully equalized with the normal-protein diet. Posthatch low-protein feeding reduced final body weight and increased feed-to-gain ratio. A significant posthatch dietary protein level × sex interaction was observed for average daily gain (P = 0.031), with the reduction occurring in males but not in females. Low-protein feeding decreased breast muscle yield (P = 0.005) and increased abdominal fat yield (P = 0.002). Serum triglyceride (P = 0.022), uric acid (P = 0.001), and several free amino acids, including Lys (P = 0.026), Thr (P < 0.001), Val (P = 0.009), Leu (P = 0.006), Ile (P = 0.030), Phe (P < 0.001), and Met (P = 0.016), were increased, whereas intestinal morphology was largely unaffected. In breast muscle, low-protein feeding increased Val (P = 0.005) and Pro (P = 0.016) concentrations and altered meat quality traits, including pH45min (P = 0.001), pH24h (P = 0.030), and b* (P < 0.001), with significant posthatch dietary protein level × sex interactions for L* (P = 0.006), a* (P = 0.003), and cooking loss (P < 0.001). Transcriptomic analysis showed sex-specific breast muscle responses, with females showing broader changes in signaling- and stress-related pathways, whereas males showed pathway changes more closely related to amino acid metabolism, protein turnover, and metabolic regulation. In conclusion, among broilers derived from low-protein-fed hens, the posthatch protein-reduced dietary strategy altered growth efficiency, carcass nutrient partitioning, amino acid profiles, breast meat quality, and breast muscle transcriptomic responses in a sex-dependent manner. These findings indicate that sex should be considered when evaluating responses to posthatch protein-reduced feeding in broilers derived from low-protein-fed hens.