Effect of Feeding High Forage Diets with Supplemental Fat on Blood Metabolites, Rumen Fermentation and Dry Matter Digestibility in Dairy Cows

Fifty mid-lactation Holstein cows were used in a six-week feeding trial to study effects of high-forage, and high-fat diets on blood constituents, rumen fermentation and dry matter digestibility. Cows were divided into 10 replicates, each consisting of five cows. Each cow was assigned to a control (diet 1) or one of the four experimental diets (high-forage (75%), high-fat (7.5%) (diet 2); high-forage. medium-fat (5.0%) (diet 3); medium forage (65%), high-fat (diet 4); medium-forage, medium-fat (diet 5)), or a control diet containing about 50% forage and 2% fat. All diets were isonitrogenous (17.7% crude protein). The forage mixture consisted of 20% alfalfa hay, 40% alfalfa haylage, and 40% corn silage. Supplemental fat included 80% rumen-protected fat and 20% yellow grease. A non-significant difference was observed in concentrations of blood glucose for cows on different experimental and control diets. Plasma nonesterified fatty acids (NEFA) were higher in cows consuming experimental diets than those consuming the control diet. However, differences in NEFA concentrations in the plasma of cows consuming diets with different forage and fat levels were not significant. Rumen pH, concentration of volatile fatty acids (VFA) in rumen contents, and dry matter digestibility of control and experimental diets, and diets with different levels of forage and supplemental fat did not differ significantly.