Abstract: [Objective] To investigate the effects of dietary supplementation with Saccharomyces cerevisiae cell wall polysaccharides （YPS） on growth performance, serum antioxidant parameters, and immune function in Tan-Hu F₁ crossbred lambs. [Methods] Sixty healthy Tan-Hu F₁ crossbred lambs, approximately 20 days old, were randomly assigned to four groups, with 15 lambs per group, each lamb serving as a replicate. The control group, experimental Group 1, experimental Group 2, and experimental Group 3 were fed pelleted lamb feed supplemented with 0%, 0.2%, 0.4%, and 0.6% YPS, respectively. The experimental period lasted 67 days, including a 7-day pre-feeding period and a 60-day formal feeding period. Lambs were weighed at the start and end of the experiment, and blood samples were collected at the end of the experiment to measure serum antioxidant and immune-related parameters. [Results] No significant differences （P>0.05） were observed among groups in initial body weight, final body weight, average daily gain, or average daily feed intake. Regarding serum antioxidant parameters, compared to the control group, experimental Group 1 exhibited significantly higher （P<0.05） activities of superoxide dismutase （SOD） and glutathione peroxidase （GSH-Px）, which were also significantly higher （P<0.05） than those in experimental Groups 2 and 3; total antioxidant capacity （T-AOC） in experimental Group 1 was not significantly different （P>0.05） from the control group but was significantly higher （P<0.05） than in experimental Groups 2 and 3; malondialdehyde （MDA） contents in experimental Group 1 were not significantly different （P>0.05） from the control group but were significantly lower （P<0.05） than in experimental Groups 2 and 3. For immune-related parameters, compared to the control group, immunoglobulin A （IgA） and immunoglobulin G （IgG） levels in experimental Groups 1 and 2 were elevated but not significantly （P>0.05）, while experimental Group 3 showed significant increases （P<0.05）; no significant differences （P>0.05） in IgA or IgG levels were observed among the three experiment groups; serum interferon-γ （IFN-γ） levels in experimental Group 1 were not significantly different （P>0.05） from the control group but were significantly lower （P<0.05） than in experimental Groups 2 and 3; serum interleukin-4 （IL-4） levels in experimental Group 1 were not significantly different （P>0.05） from the control group but were significantly higher （P<0.05） than in experimental Groups 2 and 3; serum interleukin-6 （IL-6） and tumor necrosis factor-α （TNF-α） levels in experimental Group 1 were significantly lower （P<0.05） than in the control group and significantly lower （P<0.05） than in experimental Groups 2 and 3; serum cortisol （COR） levels and diamine oxidase （DAO） activity in experimental Group 1 were not significantly different （P>0.05） from the control group but were significantly lower （P<0.05） than in experimental Groups 2 and 3; no significant differences （P>0.05） in serum D-lactate （D-LA） levels were observed among the control and experimental groups 1, 2 and 3. [Conclusion] Dietary supplementation with an appropriate level of YPS in lactating Tan-Hu F₁ crossbred lambs can enhance antioxidant capacity and immune function, alleviate weaning stress, and improve gut health. A supplementation level of 0.2%-0.4% is recommended.

Key words: Saccharomyces cerevisiae cell wall polysaccharides, Tan-Hu F₁ crossbred lambs, serum parameters, immune parameters, growth performance