热应激条件下粗饲料组合对奶牛氮素利用的影响

Effects of Forage Combinations on Nitrogen Efficiency of Dairy Cows under Heat Stress

为了研究粗饲料组合对热应激奶牛氮素利用的影响,试验选取20头胎次和泌乳天数相似的健康荷斯坦奶牛,随机分成2组,每组10头,分别饲喂2种粗饲料组合饲粮:玉米青贮+苜蓿(0.92∶1.00,AF组)和玉米秸秆(CS组)。2组饲粮精料相同,精粗比均为63.7∶36.3。预试期1周,正试期8周。结果表明:1)与CS组相比,AF组奶牛产奶量及能量校正乳、4%脂肪校正乳、乳蛋白和乳糖产量显著或极显著升高(P<0.01或P<0.05)。2)奶牛对AF组饲粮粗蛋白质表观消化率极显著高于CS组(P<0.01)。3)与CS组相比,AF组瘤胃微生物蛋白产量显著升高(P<0.05),而尿液和血液尿素氮浓度极显著降低(P<0.01)。4)与CS组相比,AF组氮摄入量和乳中氮产量极显著升高(P<0.01),但氮转化效率显著降低(P<0.05)。结果提示,与玉米秸秆相比,玉米青贮+苜蓿的组合能提高饲粮粗蛋白质水平,增加热应激奶牛粗蛋白质表观消化率,促进瘤胃微生物蛋白和乳蛋白的合成,但氮的转化效率有待提高。

In order to investigate the effects of forage combinations on nitrogen efficiency of heat-stressed cow s,tw enty healthy Holstein cow s with similar parities and days in milk were randomly divided into two groups with ten cow s per group. Cow s were fed diets with two forage combinations [corn silage ＋ alfalfa hay（ 0.92∶1.00,AF group） and corn straw（ CS group） ],but with the same concentrate and the same concentrate to forage ratio（ 63.7∶36.3）. The pretest lasted for 1 week,and the test lasted for 8 weeks. The results showed as follow s： 1） compared with CS group,cow s in AF group had significantly higher milk,energy-corrected milk,4% fat-corrected milk,milk protein and lactose yield（ P〈0. 05 or P〈0.01）. 2） Cow s showed significantly higher crude protein（ CP） apparent digestibility in AF group diet than that in CS group diet（ P 0.01）.3） Ruminal microbial protein yield in AF group was significantly higher than that in CS group（ P〈0.05）,however,urine and blood urea nitrogen concentration were significantly low er in AF group（ P〈0.01）. 4）Compared with CS group,cow s in AF group had significantly higher nitrogen intake and milk nitrogen yield（ P〈0.01）,however,had significantly lower nitrogen conversion rate（ P〈0.05）. These results indicate that compared with corn straw,the combination of alfalfa hay and corn silage can increase dietary CP level,increase CP apparent digestibility,and improve microbial protein and milk protein synthesis of heat-stressed dairy cow,however,nitrogen efficiency needs to improve.