Yaks are an important livestock species on the Tibetan Plateau, but traditional grazing practices cause a sharp drop in their weight during winter, leading to grassland degradation due to overgrazing. Although off-site fattening can improve performance and protect ecology, it often leads to a negative energy balance, liver metabolism disorders, and immune impairment due to stress. However, the effects of rumen-protected glucose (RPG) and rumen-protected taurine (RPT) on yak liver health are not yet clear. The purpose of this study was to evaluate the effects of dietary RPG and RPT levels on the growth performance, serum biochemical parameters, liver antioxidant capacity, and immunity of yaks. Twenty-eight healthy yaks weighing 170 ± 10.4 kg were randomly divided into four treatments: LGLT (RPG: 1%—low RPG [LG]; RPT: 5 g/d—low RPT [LT]), LGHT (RPG: 1%—low RPG [LG]; RPT: 20 g/d—high RPT [HT]), HGLT (RPG: 3%—high RPG [HG]; RPT: 5 g/d—low RPT [LT]), and HGHT (RPG: 3%—high RPG [HG]; RPT: 20 g/d—high RPT [HT]). The results showed that compared with the LTHT treatment group, the HGHT group upregulated the serum concentrations of glucose (p = 0.004) and Interleukin-10 (p = 0.03), the relative mRNA expression of small heterodimer partners (p = 0.01), and the sterol 12-alpha-hydroxylase (p < 0.001), while reducing the serum concentration of gamma-glutamyl transferase (p = 0.048). The serum concentration of hepatic protein carbonyl (p = 0.005) and malondialdehyde (p = 0.03) was lower in the LGHT and HGHT treatment groups than in the LGLT and HGLT groups. The relative mRNA expression of Toll-like receptor 4 (p = 0.02), Interleukin-8 (p < 0.01), and Interleukin-1β (p < 0.01) was lower in the LGHT and HGHT groups than in the LGLT and HGLT groups. Tumor necrosis factor expression was lower (p = 0.04) and glucose transporter 2 expression was higher (p < 0.01) in the HGHT group compared to other treatment groups. The expression of glucokinase, glycogen synthase, pyruvate kinase, and farnesoid X receptor was higher in the HGLT treatment group than in other treatments (p < 0.01). In conclusion, dietary supplementation with 3% PRG and 5 g/d PRT can enhance liver antioxidant capacity and immune function, reduce lipid peroxidation, and promote glucose and bile acid metabolism in yaks.

The present study evaluated the effects of dietary rumen-protected taurine (RPT) supplementation on ruminal fermentation, hematological parameters, liver function, stress-related hormones, and immune responses in yaks. Eighteen yaks were randomly allocated to three groups: a control group receiving no RPT (CON), a low-dose group receiving 20 g/day (RPT20), and a high-dose group receiving 40 g/day (RPT40). Supplementation with RPT did not significantly affect ruminal pH, microbial protein concentration, ammonia nitrogen, total volatile fatty acids, or the individual volatile fatty acid profiles (p > 0.05). A decreasing trend in red blood cell count was observed (p = 0.050), while no significant changes were detected in white blood cell or platelet indices (p > 0.05). Liver function markers, including albumin, alanine transaminase, aspartate transaminase, and total protein, remained unchanged, although a trend toward altered alkaline phosphatase activity was noted (p = 0.074). No significant effects were observed on acute-phase proteins (serum amyloid A, C-reactive protein) or stress-related hormones (epinephrine, adrenocorticotropic hormone, cortisol) (p > 0.05). Importantly, serum immunoglobulin A and immunoglobulin G levels were significantly increased in response to RPT supplementation (p = 0.029 and p = 0.043, respectively), suggesting enhanced humoral immunity. These findings indicate that RPT may improve immune function in yaks without negatively affecting rumen fermentation or liver health.