As a vital livestock breed, yaks provide meat, hides, yak milk, and other economic resources that drive economic development in the Qinghai-Tibet Plateau region. However, yak survival and productivity face challenges during cold seasons due to scarce grassland resources in the area. To maximize energy and nutrient accumulation in yaks during the green pasture period, we investigated the effects of supplementing yeast culture (YC) during this period on growth performance, immune and antioxidant capacity, rumen microbiota, and metabolites in grazing yak calves. Twelve 2-year-old calf yaks of similar body weight were randomly divided into two groups: the control group (CON) received only grazing management, while the experimental group (YEC) received 50 g/head/day of YC after grazing for 45 days. Compared with the control group, YC supplementation significantly increased the ADG of calves (P < 0. 01). And significantly reduced serum IL-1β, IL-6, TNF-α, and IFN-γ levels (P ≤ 0. 001) and MDA content (P < 0. 05), while significantly increasing serum GSH-Px, CAT, and T-AOC activities (P < 0. 01). YC supplementation also significantly increased rumen TVFA and acetate content while reducing NH₃-N levels, promoting rumen fermentation (P < 0. 05). YC supplementation reduced ruminal α-diversity, significantly increased the abundance of Proteobacteria, and decreased the abundance of Planctomycetota. These changes may indicate a decline in rumen stability. (P < 0. 05). Metabolomic analysis revealed that YC supplementation significantly altered rumen metabolite levels, primarily in glycerophospholipids, fatty acyls, prenol lipids, and steroids and steroid derivatives (P ≤ 0. 01). Furthermore, some metabolites showed strong associations with microorganisms, with RikenellaceaeRC9gutgroup and F082 significantly correlated with multiple metabolites (P < 0. 05). Results indicate that YC supplementation improves antioxidant status and reduces systemic inflammation in calf yaks, alters rumen microbial communities and metabolites, and promotes growth and development. While YC supplementation reduced the α-diversity and stability of the rumen microbiota in yaks, it concurrently increased total volatile fatty acid production. This structural reshaping, characterized by enhanced functional efficiency, warrants further investigation in future studies to assess the reversibility of such changes and their potential for practical regulation through strategies such as post-supplementation monitoring or exploring combinations with different forage types.
Peng et al. (Tue,) studied this question.