Early supplemental feeding improves post-weaning growth restriction in lambs via the gastrointestinal-metabolic axis

The weaning period often induces growth restriction in lambs due to gastrointestinal immaturity and dietary transition. Although early supplemental feeding (ESF) shows promise, its systemic mechanisms via the rumen microbiota-gut-metabolism axis remain incompletely understood. Sixty Tan lambs were assigned to a control group (suckling only), Trial Group I (free-access ESF from 10 days), and Trial Group II (free-access + forced isolation from 15 days). Growth performance, rumen fermentation, intestinal morphology, serum metabolites, and rumen microbiota were comprehensively analyzed. The supplemental feeding regimen in Trial Group I significantly improved body weight, average daily gain, and body size before and after weaning. Rumen butyrate and acetate concentrations increased markedly, with enrichment of beneficial microbiota (Bifidobacteriaceae and Sharpea). Intestinal villus height and villus-to-crypt ratio were enhanced in the jejunum and ileum. Regarding serum metabolism, lambs in both supplemental feeding groups showed significantly increased levels of albumin and urea and decreased total cholesterol. The activities of antioxidant enzymes (catalase, superoxide dismutase, and glutathione peroxidase) and the levels of oxidative products (malondialdehyde and hydrogen peroxide) in the serum of lambs from both supplemental feeding groups were significantly higher than those in the control group. Correlation analysis revealed positive associations between beneficial microbiota, fermentation parameters, intestinal development, and growth performance. ESF alleviates post-weaning growth restriction by remodeling the rumen microbiota, enhancing volatile fatty acid production, improving intestinal development, and optimizing host nutrient utilization. The free-access ESF regimen is recommended for efficient lamb production.IMPORTANCEThis study reveals that different regimens of early supplemental feeding differentially alleviate post-weaning growth restriction in lambs by distinctly remodeling the host's "rumen microbiota-gut-metabolism axis." The optimized regimen enriches beneficial rumen microbiota (e.g., Bifidobacteriaceae and Sharpea), increases key metabolite production (e.g., butyrate), and synergistically improves intestinal development and host protein/lipid metabolism, thereby elucidating the mechanism of growth promotion via microbe-host interactions. These findings advance the understanding of "nutrition-microbe-host" crosstalk in young ruminants and provide a theoretical framework for precision nutrition through microbiome modulation. The identified key microbes and metabolic functions offer potential targets for developing eco-friendly feed additives, aiding in reducing antibiotic reliance and promoting sustainable lamb production.