Effects of Concentrate Formulations on Growth Performance, Serum Metabolites, and Rumen Bacterial Communities in Finishing Yaks During Warm-Season Indoor Feeding

Optimizing concentrate supplementation is crucial for improving yak production efficiency; however, the effects of concentrate formulations under indoor fattening conditions remain unclear. Eighteen 3-year-old female finishing yaks were assigned to three concentrate formulations differing in nutrient composition, designated low (LF), medium (MF), and high (HF), with six animals per treatment. The feeding trial lasted 110 days following a 7-day adaptation period, and concentrate and roughage were offered at a ratio of 6:4 on a dry matter basis. Growth performance, serum metabolites and hormones, and rumen bacterial communities were evaluated. Final body weight and average daily gain did not differ significantly among treatments (p > 0.05). Serum total antioxidant capacity tended to be higher in the HF group than in the LF and MF groups (uncorrected p = 0.0256; BH-FDR q = 0.0768), whereas malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) did not differ significantly among treatments. This isolated numerical increase in T-AOC does not establish a general improvement in overall antioxidant status. Metabolic hormones and energy-related metabolites did not differ significantly among treatments. Rumen bacterial diversity did not differ significantly among treatments; however, the relative abundances of specific bacterial taxa differed among groups. Importantly, no direct measurements of ruminal fermentation or microbial functional activity were performed in this study. At the family level, Acidaminococcaceae and norank_o_Clostridia_UCG-014 were enriched in the MF and HF groups. At the genus level, Succiniclasticum, norank_o_Clostridia_UCG-014, and Lachnospiraceae_AC2044_group were enriched in the HF group, whereas Papillibacter was enriched in the LF group (uncorrected p < 0.05).