Effects of the dietary protein level on growth performance, nitrogen metabolism, serum biochemical index, and meat quality of Suffolk×Hu F1 lambs

This study aimed to evaluate the effects of varying dietary protein levels on growth performance, nitrogen digestion and metabolism, serum biochemical parameters, and meat quality in Suffolk × Hu F1 lambs. Thirty-six two-month-old Suffolk × Hu F1 lambs with an initial body weight of 20.58 ± 1.47 kg were randomly assigned to three dietary treatments: low protein (LP, 11.48 % crude protein), medium protein (MP, 14.36 % crude protein), and high protein (HP, 17.25 % crude protein). An adaptation period of 8 days preceded the 70-day experimental duration. The results revealed that increasing dietary protein levels, significantly improved average daily gain (ADG) and reduced feed conversion ratio (FCR) (P < 0.05). Additionally, lambs in the HP group exhibited significantly higher levels of blood urea nitrogen, serum total protein, crude protein digestion rates, nitrogen intake, urine nitrogen, nitrogen deposition, nitrogen digestion, and nitrogen digestibility compared to the LP group (P < 0.05). Notably, the HP group also showed elevated levels of total amino acids (TAA) and monounsaturated fatty acids (MUFA), as well as upregulated expression of muscle fiber-related genes IGF-1 and MyoG in the longissimus lumborum (LL) muscle, when compared to the LP group (P < 0.05). These findings suggest that increasing dietary protein intake enhances the growth performance of Suffolk × Hu F1 lambs by modulating serum biochemical markers, nitrogen digestion and metabolism, fatty acid composition, and amino acid content. Therefore, a dietary protein level of 17.25 % is recommended for optimal growth and development in two-month-old Suffolk × Hu F1 lambs.