Grings E E, Roffler R E, Deitelhoff D P
Department of Animal Science, University of Idaho, Moscow 83843.
J Dairy Sci. 1991 Aug;74(8):2580-7. doi: 10.3168/jds.S0022-0302(91)78436-1.
The effect of increasing CP levels by additions of cottonseed meal to diets for early lactation was studied in 24 multiparous Holstein cows. Diets containing 13.8, 17.5, 20.4, and 23.9% CP were fed during three 3-wk periods beginning at wk 4 postpartum. Each cow received three of the four dietary treatments giving 18 observations per treatment in a randomized complete block design. Undegraded intake protein as a fraction of total protein for the diets was .25, .32, .36, and .39. Dry matter intake increased linearly with increasing dietary CP concentrations. Daily milk yield increased as dietary CP increased from 13.8 to 17.5%. Increased milk yield was accompanied by increased daily yields of milk fat and protein, but the concentration of these components in milk was not altered. The proportion of total milk N that was NPN increased linearly with increasing dietary CP level. Plasma amino acids and urea N were increased by increasing the dietary CP level. The conclusions of the study were that increasing dietary CP levels from 13.8 to 17.5% by the use of cottonseed meal was beneficial to cows consuming alfalfa-based diets in early lactation. Increasing dietary CP above 17.5% showed little benefit in milk yield. Increasing dietary protein caused an increase in blood urea N and milk NPN, indicating N wastage by the animal.
在24头经产荷斯坦奶牛中研究了在早期泌乳日粮中添加棉籽粕提高粗蛋白（CP）水平的效果。从产后第4周开始，在三个为期3周的阶段中分别饲喂含13.8%、17.5%、20.4%和23.9% CP的日粮。每头奶牛接受四种日粮处理中的三种，在随机完全区组设计中每个处理有18个观测值。日粮中未降解摄入蛋白占总蛋白的比例分别为0.25、0.32、0.36和0.39。干物质摄入量随日粮CP浓度的增加呈线性增加。当日粮CP从13.8%增加到17.5%时，日产奶量增加。产奶量增加的同时，乳脂和乳蛋白的日产量也增加，但这些成分在牛奶中的浓度没有改变。牛奶中非蛋白氮（NPN）占总氮的比例随日粮CP水平的增加呈线性增加。日粮CP水平升高会使血浆氨基酸和尿素氮增加。该研究的结论是，在早期泌乳期，使用棉籽粕将日粮CP水平从13.8%提高到17.5%对采食苜蓿型日粮的奶牛有益。日粮CP超过17.5%对产奶量几乎没有益处。日粮蛋白质增加导致血液尿素氮和牛奶NPN增加，表明动物存在氮浪费。
