Evaluation of diets containing supplemental fat with different sources of carbohydrates for lactating dairy cows.

A study was conducted to evaluate the lactational response of high producing cows to diets supplemented with fat that contained additional ruminally degradable carbohydrate from a molasses plus fat product and dried whey. Forty Holstein cows were randomly assigned within lactation group to receive diets containing 2% tallow with or without molasses or dried whey wk 4 through 16 postpartum. Cows were fed 1) the control TMR of 25% corn silage, 25% alfalfa hay, and 50% concentrate mix, 2) the TMR containing fat, 3) the TMR containing molasses and fat, or 4) the TMR containing dried whey and fat. Production of milk and 3.5% FCM was increased by supplemental fat. Milk protein and fat percentages were not affected by supplemental fat with or without molasses or dried whey. The DMI and BW were similar for all diets. Production efficiency (3.5% FCM/DMI) was higher for cows fed supplemental fat diets, and cows fed tallow alone were more efficient than those fed tallow with molasses or dried whey. Tallow did not influence ruminal concentrations of various VFA. Molar percentage of butyrate was higher for cows fed the TMR containing molasses plus fat or dried whey plus fat than for cows fed the TMR containing fat. The TMR containing 2% tallow increased milk production, but no economic advantage was derived from inclusion of an additional ruminally fermentable carbohydrate as molasses or from dried whey with fat.