Dietary choline for the lactating cow: possible effects on milk fat synthesis.

Two experiments with low forage diets tested effects of added dietary choline on milk fat synthesis. In Experiment 1, 18 Holstein cows were in a 12-wk trial. Choline (0, 1.5, and 3 g/kg) was added to the concentrate portion of a 70% concentrate, 30% corn silage diet (dry matter). Treatments were applied in a switchback design with 4-wk experimental periods. Highest choline increased milk fat by .34 percentage units and fat-corrected milk by 2 kg per day over controls. Rumen pH and volatile fatty acids were similar among treatments. Free fatty acids of blood serum were reduced 3.0 mg/100 ml by 3 g/kg choline. In Experiment 2 with four mature Holsteins, choline was added (0, 2, 4, and 6 g/kg concentrate) in 25% corn silage and 75% concentrate diets. Treatments were applied in a 4 x 4 Latin square design. Addition of 4 g/kg choline resulted in 3.7 kg/day and .77 percentage unit increases of fat-corrected milk and milk fat percent, respectively, whereas fat-corrected milk and milk fat percent at 6 g/kg were only slightly higher than controls. We hypothesized that choline aided transport of mobilized free fatty acids from adipose tissue through the liver to the mammary gland.