Effects of two supplementary feeding strategies on growth performance, antioxidant status, immune responses, gut microbiota, and short-chain fatty acids in free-ranging yak calves

Yaks are essential food resources on the Qinghai-Xizang Plateau, and efficient breeding is critically important for local development. However, little is known about the effect of supplementary feeding on free-ranging yaks in Ngari Prefecture. Therefore, this study was performed to explore the effect of supplementary feeding on the growth of yaks, antioxidant ability, immunity, intestinal microbiota, and short-chain fatty acids (SCFAs) in yaks. A total of thirty ( n = 30) yak calves were randomly grouped into control group (OC, n = 10), supplementary feeding group #1 (OF, n = 10), and supplementary feeding group #2 (OT, n = 10), and yaks in group OC were free-ranged, while yaks in group OF were extra daily fed with Oat grass (2.8 kg/head), alfalfa (2.8 kg/head) and commercial concentrated food (1.4 kg/head), and yaks in group OT were extra daily fed with Oat grass (2.5 kg/head), alfalfa (2.5 kg/head) and commercial concentrated food (2.0 kg/head) for six weeks. Results showed that the body weight of yaks in OT was significantly higher than in group OC ( P < 0.001) and OF ( P < 0.01). Immunoglobulin examination revealed that IgA in group OT and OF was observably higher than group OC ( P < 0.05, P < 0.001). Serum oxidation ability detection found that T-AOC ( P < 0.01, P < 0.01), GSH-Px ( P < 0.01, P < 0.001) and SOD ( P < 0.05, P < 0.05) in group OF and OT were significantly higher than in group OC, while MDA was obviously higher in group OC ( P < 0.05). Serum inflammatory factors evaluation of yaks showed that TNF-α ( P < 0.01, P < 0.001), IL-6 ( P < 0.05, P < 0.01), IL-1β ( P < 0.05, P < 0.05), IL-2 ( P < 0.01, P < 0.01), and IL-8 ( P < 0.05, P < 0.01) in group OF and OT were significantly lower than OC group, while IL-10 was observably lower in group OC ( P < 0.05). Amplicon sequencing of the rectal content microbiota of yaks in the third week and sixth week achieved 571 477 and 643 058 filtered sequences, respectively. In the third week, the abundance of three phyla (Verrucomicrobiota, Elusimicrobiota, Thermoproteota) and twelve genera ( Bulleidia , Limivicinus , Paramuribaculum , SFLA01, etc.) were obviously different among different yak groups, while one phylum (Actinobacteriota) and twenty genera ( Arthrobacter B, Romboutsia B, Scatocola , Faecimonas , etc.) were obviously different among different yak groups in the sixth week. Overall, the supplementation of growth performance, antioxidant capacity, immune responses, intestinal microbiota, and intestinal SCFA profile was positively correlated with the introduction of supplementary feeding in yak calves on the plateau. These results support the possibility of applying targeted additional feeding methods to improve yak production in cold conditions of high altitudes, and can help to develop more effective nutritional management of ruminants in plateau areas.