Effects of Postruminal Protein on Fatty Acid Digestibility in Dairy Cows

¹ Department of Dairy Science, University of Wisconsin, Madison 53706

Eight ruminally cannulated Holstein cows (four multiparous and four primiparous) were used in a replicated 4 x 4 Latin square with an extra period to determine the effects of postruminal protein on fatty acid digestibility. Samples were collected during the last 4 d of each 14-d period. Total mixed rations were composed of 41% alfalfa haylage, 42% corn silage, 12% concentrate based on corn, and 5% tallow. Cows were fed at 90% of ad libitum intake. Treatments were abomasal infusion of guar gum or guar gum plus urea, corn gluten meal, or blood meal in 12 L of water. The basal ration contained 12% crude protein (CP), and infusion of N sources increased CP to approximately 14%. Dry matter intake was similar for cows on all treatments. Milk, 3.5% fat-corrected milk, milk protein, and milk fat yields increased for cows receiving postruminal CP. Postruminal CP did not affect milk fat and protein percentages. Dry matter, organic matter, and CP digestibilities were greater in cows receiving postruminal CP. Total fatty acid and total C₁₈ fatty acid digestibilities were not affected by treatment. Total C₁₆ fatty acid and C_18:0 fatty acid digestibilities were greater for cows receiving nonprotein N than for those receiving true protein.

Key Words: postruminal protein • fatty acid digestibility • dairy cows • animal proteins

Submitted on November 29, 1995
Accepted on February 19, 1998