Christensen R A, Cameron M R, Clark J H, Drackley J K, Lynch J M, Barbano D M
Department of Animal Sciences, University of Illinois, Urbana 61801.
J Dairy Sci. 1994 Jun;77(6):1618-29. doi: 10.3168/jds.S0022-0302(94)77104-6.
The objectives of this experiment were to investigate the effects of amount of dietary CP and ruminally protected AA supplementation on production of milk and milk components, ruminal fermentation, and nutrient digestibilities by cows fed diets containing high oil corn and tallow. Holstein cows in midlactation producing 22 to 25 kg/d of milk were used in a 5 x 5 Latin square design. Treatments were 1) control (16.8% CP, no added fat); 2) 14.2% CP, no AA; 3) 14.2% CP, with AA; 4) 17.5% CP, no AA; and 5) 17.5% CP, with AA. Diets 2 to 5 contained supplemental fat from high oil corn and tallow. Diets consisted of 33% alfalfa haylage, 17% corn silage, and 50% concentrate DM. Intake of DM was not different among treatments. Dietary fat increased yields of milk, fat, SNF, and total solids and percentages of fat and total solids. Increasing CP from 14.2 to 17.5% did not alter production or composition of milk. Supplemental AA increased yields of 4% FCM, milk fat, milk CP, true protein, and casein protein and percentages of CP, true protein, and casein protein in milk when either 14.2 or 17.5% CP was in the diet. Supplemental fat did not alter ruminal fermentation, but increases in dietary CP increased total VFA concentration in the rumen without affecting proportions of individual VFA. Apparent digestibilities of DM, OM, CP, starch, and energy in the total tract were greater for cows fed the 17.5% CP diets. Addition of AA to the 14.2% CP diet increased apparent digestibilities of DM, OM, ADF, NDF, and energy in the total tract but decreased digestibilities for cows fed the 17.5% CP diets. Feeding AA to midlactation cows in diets containing supplemental fat may alleviate the decrease in milk protein percentage associated with fat supplementation; this response was similar for cows fed diets that contained either 14.2 or 17.5% CP.
本试验旨在研究日粮粗蛋白（CP）含量和瘤胃保护性氨基酸（AA）添加量对采食含高油玉米和牛脂日粮奶牛的产奶量、乳成分、瘤胃发酵及养分消化率的影响。采用5×5拉丁方设计，选用处于泌乳中期、日产奶量22至25千克的荷斯坦奶牛。处理组分别为：1）对照组（CP含量16.8%，不添加脂肪）；2）CP含量14.2%，不添加AA；3）CP含量14.2%，添加AA；4）CP含量17.5%，不添加AA；5）CP含量17.5%，添加AA。日粮2至5含有来自高油玉米和牛脂的补充脂肪。日粮由33%苜蓿青贮、17%玉米青贮和50%精料干物质组成。各处理组间干物质采食量无差异。日粮脂肪提高了产奶量、乳脂、非脂固形物（SNF）、总固形物产量以及乳脂和总固形物百分比。将CP含量从14.2%提高到17.5%未改变产奶量或乳成分。当日粮CP含量为14.2%或17.5%时添加AA均提高了4%乳脂校正乳（FCM）、乳脂、乳CP、真蛋白和酪蛋白产量以及乳中CP、真蛋白和酪蛋白百分比。补充脂肪未改变瘤胃发酵，但日粮CP含量增加提高了瘤胃总挥发性脂肪酸（VFA）浓度，且不影响各VFA比例。采食CP含量17.5%日粮的奶牛全消化道干物质、有机物、CP、淀粉和能量的表观消化率更高。在CP含量14.2%的日粮中添加AA提高了全消化道干物质、有机物、酸性洗涤纤维（ADF）、中性洗涤纤维（NDF）和能量的表观消化率，但降低了采食CP含量17.5%日粮奶牛的消化率。在含补充脂肪的日粮中给泌乳中期奶牛饲喂AA可缓解因补充脂肪导致的乳蛋白百分比下降；采食CP含量14.2%或17.5%日粮的奶牛对此反应相似。
