Alstrup L, Weisbjerg M R, Hymøller L, Larsen M K, Lund P, Nielsen M O
Department of Animal Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark.
Department of Animal Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark.
J Dairy Sci. 2014 Jul;97(7):4412-22. doi: 10.3168/jds.2013-7585. Epub 2014 May 16.
The aim of this experiment was to examine whether the positive response in milk production to increased crude protein (CP) supply in dairy cows was dependent on the digestibility of the forage. Forty-eight lactating Danish Holstein cows were used in a 4 × 4 Latin square design experiment with 4 rations: (1) high digestibility and high CP concentration (HdHp), (2) high digestibility and low CP concentration (HdLp), (3) low digestibility and high CP concentration (LdHp), and (4) low digestibility and low CP concentration (LdLp). All rations contained 30% corn silage, 25% grass-clover silage, and 45% concentrate on a dry matter (DM) basis. Different digestibilities were obtained by replacing a high-digestible grass-clover silage combined with a high-digestible corn silage with a low-digestible grass-clover silage combined with a low-digestible corn silage. Organic matter digestibilities were 79.8 and 74.7% in the high- and low-digestibility rations, respectively. Dietary CP concentration in the ration was increased by substituting barley and sugar beet pulp with rapeseed meal and soybean meal, whereby CP increased from 13.9 to 14.0% (Lp) to 15.7 to 16.0% (Hp). All cows were offered 3 kg of the same concentrate per day in the automatic milking system in addition to the mixed ration. Every feeding period lasted 3 wk, and DM intake and milk yield were measured in the last week in each period, and milk samples for determining milk composition, including fatty acid content, and blood samples were taken during the last 3d of each period. Dry matter intake increased by 2.2 kg/d on Hd compared with Ld and by 0.7 kg/d on Hp compared with Lp. The positive effect on DM intake was reflected in the energy-corrected milk (ECM) yield, as a higher ration digestibility increased the ECM yield by 1.7 kg/d and a higher CP concentration increased it by 1.2 kg/d. We detected no interaction between forage digestibility and CP concentration on milk production. Reduced digestibility was accompanied by an increase in the plasma level of glucose, suggesting that other nutrients were limiting to milk production. In conclusion, milk production responses to dietary CP supply appeared independent of forage digestibility.
本实验的目的是研究奶牛产奶量对粗蛋白（CP）供应增加的积极反应是否取决于饲草的消化率。48头泌乳期丹麦荷斯坦奶牛用于一项4×4拉丁方设计实验，有4种日粮：（1）高消化率和高CP浓度（HdHp），（2）高消化率和低CP浓度（HdLp），（3）低消化率和高CP浓度（LdHp），以及（4）低消化率和低CP浓度（LdLp）。所有日粮按干物质（DM）计，包含30%玉米青贮、25%三叶草青贮和45%精料。通过用低消化率的三叶草青贮和低消化率的玉米青贮替代高消化率的三叶草青贮和高消化率的玉米青贮来获得不同的消化率。高消化率和低消化率日粮的有机物消化率分别为79.8%和74.7%。通过用菜籽粕和豆粕替代大麦和甜菜粕来提高日粮中的CP浓度，CP含量从13.9%至14.0%（Lp）提高到15.7%至16.0%（Hp）。除混合日粮外，所有奶牛每天在自动挤奶系统中饲喂3千克相同的精料。每个饲喂期持续3周，在每个时期的最后一周测量干物质摄入量和产奶量，并在每个时期的最后3天采集用于测定牛奶成分（包括脂肪酸含量）的牛奶样本和血样。与低消化率日粮相比，高消化率日粮使干物质摄入量每天增加2.2千克；与低CP浓度日粮相比，高CP浓度日粮使干物质摄入量每天增加0.7千克。对干物质摄入量的积极影响反映在能量校正乳（ECM）产量上，较高的日粮消化率使ECM产量每天增加1.7千克，较高的CP浓度使其每天增加1.2千克。我们未检测到饲草消化率和CP浓度对产奶量有交互作用。消化率降低伴随着血浆葡萄糖水平升高，这表明其他营养素限制了产奶量。总之，日粮CP供应对产奶量的反应似乎与饲草消化率无关。
