No abstract

Twenty-four Holstein cows in wk 3 through 12 of lactation were used to evaluate distillers dried grains with solubles as a protein source for alfalfa-based diets. Diets were formulated containing 0, 10.1, 20.8, or 31.5% distillers dried grains with solubles. Crude protein in these diets was 13.9, 16.0, 18.1, and 20.3%. Milk yield increased linearly with increasing dietary CP, whereas DMI was not affected. Dry matter intake averaged over 4% of BW for all treatments. Intake of undegraded intake protein was .93, 1.27, 1.63, and 1.97 kg/d. Yields of milk protein, casein, and lactose all increased linearly with increasing dietary CP. The proportion of milk N as whey N decreased, whereas N as NPN increased, with increasing dietary CP. Plasma urea N and essential and branched-chain AA increased linearly, and nonessential AA decreased linearly, with increasing dietary CP. Increasing the concentration of CP in the diet from 13.9 to 18.1% by the addition of distillers dried grains with solubles was beneficial to cows fed alfalfa-based diets in early lactation. Little additional benefit was observed by feeding greater than 18.1% dietary CP.

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.