The objective of this experiment was to investigate the potential benefits of active dry yeast (ADY) on the growth performance, rumen fermentation, nutrient digestibility, and serum parameters of weaned beef calves. Thirty Simmental crossbred male calves (body weight = 86.47 ± 4.41 kg and 70 ± 4 d of age) were randomly divided into 2 groups: control (CON) (fed basal ration) and ADY (fed basal ration and 5 g/d ADY per calf). The dietary concentrate-to-roughage ratio was 35:65. All the calves were regularly provided rations 3 times a day at 07:00, 13:00, and 19:00 and had free access to water. The experiment lasted for 60 d. The average daily gain of ADY group was higher (P = 0.007) than that of the CON group, and the ratio of feed intake to average daily gain in the ADY group was reduced (P = 0.022) as compared to the CON group. The concentration of ruminal ammonia-N was higher (P = 0.023) in the CON group than that in the ADY group, but an opposite trend of microbial protein was found between the 2 groups. Also, the ruminal concentrations of propionate and butyrate were higher (P < 0.05) in the ADY group than those in the CON group. Calves fed ADY exhibited higher (P < 0.05) crude protein and neutral detergent fiber digestibility. Supplementation of ADY increased (P < 0.05) the contents of glucose, glutathione peroxidase, superoxide dismutase, immunoglobulin A, immunoglobulin M, and interleukin 10 in the serum of calves, but an opposite trend was observed in malondialdehyde, interleukin 1 beta, and tumor necrosis factor alpha contents between the 2 groups. In conclusion, dietary supplementation with ADY could improve the growth performance, rumen fermentation, nutrient digestibility, antioxidant ability, and immune response of weaned beef calves.

本实验的目的是研究活性干酵母 (ADY) 对断奶小牛的生长性能、瘤胃发酵、营养消化率和血清参数的潜在益处。30头西门塔尔杂交雄性小牛（体重= 86.47±4.41 kg和70±4天龄）随机分为2组：对照组（CON）（饲喂基础日粮）和ADY（饲喂基础日粮和5 g/d ADY）小牛）。日粮精料与粗料的比例为 35:65。所有的小牛在 07:00、13:00 和 19:00 每天定期提供 3 次口粮，并且可以自由饮水。实验持续60 d。ADY组平均日增重高于 CON组（P = 0.007），ADY组采食量与平均日增重比降低（P = 0.022) 与 CON 组相比。 CON组瘤胃氨氮浓度高于ADY组（P =0.023），但2组间微生物蛋白呈相反趋势。此外， ADY 组的瘤胃丙酸盐和丁酸盐浓度高于CON 组（P < 0.05）。饲喂 ADY 的犊牛表现出更高的 ( P  < 0.05) 粗蛋白和中性洗涤纤维消化率。补充ADY增加（P < 0.05) 小牛血清中葡萄糖、谷胱甘肽过氧化物酶、超氧化物歧化酶、免疫球蛋白 A、免疫球蛋白 M 和白介素 10 的含量，但丙二醛、白介素 1 β 和肿瘤坏死因子 α 的含量呈相反趋势。 2组。总之，日粮添加ADY可以改善断奶牛犊的生长性能、瘤胃发酵、营养消化率、抗氧化能力和免疫反应。