Effect of diets with different protein levels on the transformation of muscle fiber types and meat characteristics of Tibetan sheep

This experiment aimed to study the effects of different protein level rations on meat quality and histological characteristics of muscle fibers in Tibetan lambs. Ninety two-month-old plateau-type Tibetan lambs weighing (15.40 ± 0.81 kg) were selected and randomly divided into three treatment groups of 30 lambs each, and fed diets with protein levels of 10.20% (group L), 11.58% (group M), and 13.03% (group H). The diets were fed to the animals at the same time. The results showed that the antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px), catalase (CAT), and superoxide dismutase (SOD) activity levels of Tibetan sheep muscles in group L were significantly lower than those in group M (P < 0.05). The elasticity of the muscles in group M was significantly higher than that of the muscles in groups H and M (P < 0.05); muscle chewiness and adhesion were significantly lower in group M than in groups L and H (P < 0.05); the diameter of the type-Ⅰ, Ⅱa, and Ⅱb muscle fibers was significantly greater in group H than in group L (P < 0.05), and the diameter of the type-Ⅰ, Ⅱa, and Ⅱb muscle fibers was significantly greater in group M than in group L (P < 0.05); the densities of the type-Ⅰ, Ⅱa, and Ⅱb muscle fibers in group M were significantly higher than in group H (P < 0.05); the number and area ratio of oxidized muscle fibers were significantly higher in group M than in group L (P < 0.05); the expression level of MyHCⅠ was significantly higher in group L than in group M vs. group H; the MyHC IIa expression level in group M was significantly higher than in group L, and the MyHC IIb expression level in group L was significantly higher than in groups M and H (P < 0.05). The gene expression levels of MyHC I and MyHC IIa were significantly negatively correlated with masticatory property (P < 0.05). The gene expression level of MyHC II significantly correlated with T-AOC (P < 0.05). Gene expression was significantly negatively correlated with T-AOC (P < 0.05) and significantly positively correlated with chewability and hardness (P < 0.05). In conclusion, in this experiment, a protein level of 11.58% in the ration improved the muscle fiber characteristics of the longest dorsal muscle of Tibetan sheep, enhanced the transformation of muscle fibers from enzymatic to oxidative, and increased the proportion of the oxidative area, which could be beneficial to the improvement of meat quality.