Fermented feed-rumen microbiota axis mediates goat kid growth via microbial amino acid synthesis and ruminal epithelial energy metabolism.

Pretreating feed via fermentation to enhance its nutritional value is effective for young ruminants. This study optimized fermented feed using a microbial consortium of Saccharomyces cerevisiae, Bacillus licheniformis, and Enterococcus faecalis, and explored its mechanisms on growth performance and ruminal function in goat kids. The Bacillus licheniformis is the most critical determinant of the nutritional value of FF. Optimized FF had higher levels of crude protein, calcium, phosphorus, and limiting amino acids (AA). The FF contained viable microbiota with lower diversity but greater evenness. The microbiota was enriched in AA and carbohydrate metabolism by enhancing the abundance of Leuconostoc lactis and Lactococcus lactis. A 40-day feeding trial was then conducted with 20-day-old goat kids. Compared to conventional feed, FF increased feed digestibility, body weight and carcass weight. Mechanistically, FF enhanced the interactions among rumen microbes and increased the gene abundance related to carbohydrate and AA metabolism. The FF then upregulated expression of mitochondrial respiratory chain-related genes in the rumen epithelium, thereby improving epithelial energy metabolism. Overall, this study shows that fermented feed optimized by microbial consortium improves goat kid growth and carcass quality through the fermented feed-rumen microbiota axis, offering a sustainable approach for ruminant production.