饲粮碳水化合物组成对奶牛氮利用率的影响

摘要

本试验旨在研究饲粮碳水化合物组成对奶牛氮利用率的影响。采用4×4拉丁方设计,选用8头荷斯坦头胎奶牛作为试验动物,4头安装永久瘤胃瘘管,每个处理2头,安装和未安装瘘管的奶牛各1头。采用饲粮中性洗涤纤维与淀粉比例( NDF∶starch )表示饲粮碳水化合物组成,通过改变饲粮中燕麦草、玉米青贮以及玉米的比例设计4种不同碳水化合物组成饲粮, NDF∶starch分别为0.86、1.18、1.63和2.34。每期试验21 d,其中适应期14 d,采样期7 d。结果发现：1)乳蛋白产量与粗蛋白质采食量相关性最强( r=0.874,P<0.05),次之为可代谢蛋白质产量( r=0.700,P<0.05)和微生物蛋白产量( r=0.484,P<0.05)；2)随着饲粮NDF∶starch的增加,饲粮粗蛋白质转化为乳蛋白效率呈显著二次曲线关系( P<0.05),饲粮粗蛋白质转化为可代谢蛋白质效率呈线性升高趋势(0.05≤P<0.10),可代谢蛋白质转化为乳蛋白效率呈二次曲线趋势(0.05≤P<0.10),微生物蛋白转化为乳蛋白效率、饲粮粗蛋白质转化为微生物蛋白效率与微生物蛋白转化为可代谢蛋白质效率无显著变化( P>0.05)；当饲粮NDF∶starch为1.71时,奶牛饲粮粗蛋白质转化为乳蛋白效率最高,达到27.6%；3)随着饲粮NDF∶starch的增加,尿中尿素氮含量呈先降低后升高的二次曲线变化趋势(0.05≤P<0.10),乳中和血液尿素氮含量呈显著的线性升高( P<0.05)。综合以上,奶牛饲粮碳水化合物组成能够影响氮利用率,随着饲粮NDF∶starch的增加,奶牛饲粮粗蛋白质转化为乳蛋白效率呈二次曲线变化。在本饲粮条件下,奶牛饲粮NDF∶starch为1.71时能够获得最佳的氮利用率。%This study was designed to investigate the effects dietary carbohydrate composition on nitrogen effi-ciency of dairy cows. Eight primiparous including four rumen cannulated dairy cows were assigned to 4 treat-ments in a 4×4 Latin square design with two cows in each treatment (1 normal cow and 1 rumen cannulated cows) . Dietary carbohydrate composition was expressed as ratio of neutral detergent fiber to starch ( NDF ∶starch). Oat hay, corn silage and corn were used to adjust dietary NDF∶starch, and NDF∶starch was 0.86, 1.18, 1.63 and 2.34, respectively. The experiment had four periods, each period was 21 d containing 14 d of adaptation and 7 d of sampling. The results showed as follows: 1) the correlation between milk protein yield and crude protein intake was the highest (r=0.874, P<0.05), which was followed by metabolizable protein ( MP) yield ( r=0.700, P<0.05) and microbial protein ( MCP) yield ( r=0.484, P<0.05);2) with the in-crease of dietary NDF∶starch, significantly quadratic relationship with the efficiency of dietary crude protein in-take to milk protein was observed ( P<0.05) , linear increasing trend of the efficiency of dietary crude protein to metabolizable protein was observed (0.05≤P<0.10), and quadratic trend of the efficiency of metabolic protein to milk protein was observed (0.05≤P<0.10), while no significant effects were observed in efficien-cies of microbial protein to milk protein, dietary crude protein to microbial protein and microbial protein to me-tabolizable protein (P>0.05); when dietary NDF∶starch was 1.71, the efficiency of dietary crude protein to milk protein reached the highest level of 27.6%;3) with the increase of dietary NDF∶starch, the content of u-rea nitrogen in urine showed a trend of quadratic change (0.05≤P<0.10), however, the content of urea nitro-gen in blood and milk were significantly linearly increased ( P<0.05) . Therefore, dietary carbohydrate compo-sition can affect nitrogen utilization, and with the increase of dietary NDF∶starch, quadratic increase of the ef-ficiency of dietary crude protein to milk protein can be observed. Dietary NDF∶starch of 1.71 can obtain the optimal nitrogen efficiency in dairy cows under the conditions of the present diet.