Effects of Rumen-Protected Glycine and Methionine Supplementation in a Low-Protein Diet on Growth and Development, Slaughter Performance, Meat Quality, and Rumen Microflora of Yudong Black Goats

This study aimed to investigate the effects of supplementing rumen-protected glycine and methionine to low-protein diets on the growth and development of Yudong black goats. Sixty 4-month-old Yudong black goats with comparable body weights (21.0 ± 0.74 kg) were randomly assigned to four groups: the control (CON), rumen-protected glycine (GLY), rumen-protected methionine (MET), and mixed-amino-acid (MAG) groups. The CON group was fed a basal diet containing 13.4% crude protein, whereas the GLY, MET and MAG groups received diets with 11.0% crude protein supplemented with 4 g/kg rumen-protected glycine, 4 g/kg rumen-protected methionine, and 2 g/kg rumen-protected glycine + 2 g/kg rumen-protected methionine, respectively. The experimental period lasted 60 days. Compared with the CON group, supplementation with glycine or methionine alone did not affect the growth performance of goats (p > 0.05). However, the MAG group exhibited significantly increased longissimus muscle area and C20:3n6 content, together with a significant reduction in ALB (p < 0.05). In addition, the relative abundance of Prevotella was significantly higher in the MET group than in the CON group (p < 0.05), and strong correlations existed between dominant ruminal bacterial genera and indicators of growth and slaughter performance. In conclusion, supplementation with rumen-protected amino acids in low-protein diets can markedly improve slaughter performance and meat quality of Yudong black goats without impairing their growth or normal physiological metabolism.