Fifty cows were used to evaluate the lactational response to diets containing additional fat as tallow and increased amounts of RUP (bypass proteins) with or without molasses. Cows were blocked by parity and calving date and randomly assigned to one of five diets from wk 4 to 16 postpartum. Treatments were 1) control (soybean meal), 2) bypass proteins (blood meal, meat and bone meal, corn gluten meal, soybean meal), 3) molasses and bypass proteins, 4) fat and bypass proteins, and 5) molasses, fat, and bypass proteins. Cows were fed for ad libitum intake a total mixed diet that contained 25% corn silage, 25% alfalfa hay, and 50% concentrate mix (dry matter basis). Production of milk was higher for cows fed diets containing fat and bypass proteins; molasses and bypass proteins; and molasses, fat, and bypass proteins than for cows fed the diet with bypass proteins alone, but production was similar for cows fed the control diet and diets containing bypass proteins alone. Production of milk was similar for cows fed the diet with molasses and bypass proteins and for cows fed the diet with fat and bypass proteins. Milk protein percentages were higher for cows fed the diet with molasses and bypass proteins than for those fed the diet containing fat and bypass proteins. The dry matter intake, body weight gains, and body condition scores were unaffected by treatment. For all diets, Met, Lys, and Phe were the first three limiting essential amino acids for milk protein synthesis. Production was increased by including either fat or molasses with bypass protein, but there was no clear advantage of including both fat and molasses in the diet.
Bibliographical noteFunding Information:
The authors gratefully acknowledge Fats and Proteins Research Foundation, Inc. (Bloomington, IL) for partial financial support. Appreciation is extended to Valley Queen Cheese (Milbank, SD) for mid infrared milk analysis. Appreciation also is extended to Fenton Ludens, herdsman, and the farm crew at the South Dakota State University Dairy Research Unit for management of the cows and for assistance with collection of data.
- Animal fat
- Lactating dairy cows
- Ruminally undegradable protein