本试验旨在研究不同酵母培养物（YC）对泌乳中后期奶牛生产性能、养分表观消化率以及血清指标的影响。选取48头健康的泌乳中后期荷斯坦奶牛，按照胎次、产奶量[（36.49±1.50）kg]、泌乳天数[（175±6）d]等相同或相近的原则随机分为对照组、试验Ⅰ组、试验Ⅱ组和试验Ⅲ组，每组12个重复，每个重复1头牛。对照组在基础饲粮基础上添加500 g/（d·头）的压片玉米，试验Ⅰ组、试验Ⅱ组和试验Ⅲ组分别在基础饲粮基础上添加500 g/（d·头）的酵母培养物1、500 g/（d·头）的酵母培养物2、100 g/（d·头）的酵母培养物3。试验期45 d，其中预试期为15 d，正试期为30 d。结果表明：1）与对照组相比，试验Ⅰ组的干物质采食量显著提高0.82 kg/d（P<0.05），产奶量显著增加1.18 kg/d（P<0.05）；试验Ⅱ组和试验Ⅲ组干物质采食量分别提高0.58、0.66 kg/d，产奶量分别提高0.79、0.65 kg/d，差异均不显著（P>0.05）。试验Ⅰ组乳成分中乳脂率分别比对照组和试验Ⅱ组显著提高5.12%和4.83%（P<0.05）；与对照组相比，试验Ⅱ组和试验Ⅲ组乳脂率分别提高0.26%和2.70%，差异不显著（P>0.05）。2）试验Ⅰ组干物质、中性洗涤纤维的表观消化率分别比对照组显著提高5.47%和3.05%（P<0.05）；试验Ⅱ组和试验Ⅲ组干物质、中性洗涤纤维的表观消化率比对照组分别提高3.71%和1.84%、1.36%和0.96%，但差异不显著（P>0.05）。3）试验Ⅰ、Ⅲ组血清球蛋白含量在第0天显著高于对照组（P<0.05）；试验Ⅲ组血清球蛋白含量在第15天及全期平均值显著高于对照组（P<0.05）。4）与对照组相比较，试验Ⅰ组血清丙二醛含量在第30天及全期平均值显著降低（P<0.05）；试验Ⅰ组血清谷胱甘肽过氧化酶活性在第15天及全期平均值显著高于对照组（P<0.05）。5）与对照组相比，试验Ⅰ组毛利润提高2.14元/（d·头），其他组均降低。综合分析得出，饲粮中添加酵母培养物能够提高泌乳中后期奶牛生产性能，提高养分表观消化率，对血清生化指标没有负面影响，同时增强血清抗氧化能力，提高经济效益，以添加500 g/（d·头）的酵母培养物1效果较好。

This experiment was conducted to investigate the effects of different yeast cultures on performance, nutrient apparent digestibility and serum indexes of dairy cows in mid-and late-lactation. Fifty-eight healthy Holstein cows in mid-and late lactation were randomly divided in to 4 groups with 12 replicates per group and 1 cow per replicate based on similar parity, milk yield[(36.49±1.50) kg] and duration of lactation[(175±6) d]. Control group was fed a basal diet supplemented with 500 g/(d·head) tablet corn, test group Ⅰ, test group Ⅱ and test group Ⅲ were fed the basal diet supplemented with 500 g/(d·head) yeast culture 1, 500 g/(d·head) yeast culture 2 and 100 g/(d·head) yeast culture 3, respectively. The test lasted for 45 d, including 15 d for pre-test and 30 d for formal test. The results showed as follows:1) compared with control group, dry matter intake of test group Ⅰ significantly increased by 0.82 kg/d (P<0.05), and milk yield significantly increased by 1.18 kg/d (P<0.05); dry matter intake of test group Ⅱ and test group Ⅲ increased by 0.58 and 0.66 kg/d, respectively, and milk yield increased by 0.79 and 0.65 kg/d, respectively, but the differences were not significant (P>0.05). Compared with control group and test group Ⅱ, milk fat percentage of test group Ⅰ significantly increased by 5.12% and 4.83% (P<0.05), respectively; compare with control group, milk fat percentage of test group Ⅱ and test group Ⅲ increased by 0.26% and 2.70% (P>0.05), respectively. 2) Apparent digestibility of dry matter and neutral detergent fiber of test group Ⅰ were significantly increased by 5.47% and 3.05% than those of control group (P<0.05); apparent digestibility of dry matter and neutral detergent fiber of test group Ⅱ and test group Ⅲincreased by 3.71% and 1.84%, 1.36% and 0.96% than those of control group, but the differences were not significant (P>0.05). 3) Serum globulin content of test group Ⅰ and test group Ⅲ on day 0 was significantly higher than that of control group(P<0.05); serum globulin content of test group Ⅲ on day 15 and whole period average value were significantly higher than those of control group(P<0.05). 4) Compared with control group, serum malondialdehyde (MDA) content of test group Ⅰ on day 30 and whole period average value were significantly lower (P<0.05); serum glutathione peroxidase activity of test group Ⅰ on day 15 and whole period average value were significantly higher than those of control group (P<0.05). 5) Compared with control group, gross profit of test group Ⅰ increased by 2.14 RMB/(d·head), while other groups decreased. In conclusion, diet supplemented with yeast culture can improve performance and nutrient apparent digestibility, not negatively affects serum biochemical indexes, enhance serum antioxidant capacity, and improve economic efficiency; the effects of 500 g/(d·head) yeast culture 1 are the best.