Dietary choline effects on milk yield and duodenal choline flow in dairy cattle.

In Experiment 1, the effect, in early lactation, of 0 or 3 g of supplemental choline/kg of total diet DM on milk yield and composition was tested in 20 first lactation and older Holstein cows. In Experiment 2, 30 first lactation and older Holstein cows between 45 and 200 d postpartum were assigned to treatments of 0, 2.5, and 5.0 g of supplemental choline/kg of total diet DM to test the effect of dietary choline with diets based on corn and soybean meal. In Experiments 1 and 2, added choline had no effect on either milk yield or fat-corrected milk yield. In both experiments, fat yield and fat percentage tended to increase with choline supplementation, but protein yield and protein percentage were unaffected. In Experiment 1, choline had no effect on serum lipids. Ruminal dosing of steers with 27 g/d supplemental choline in Experiment 3 increased duodenal choline flow by only 3 g/d. The apparent rumen degradability of choline tended to be higher (77.1 vs. 70.6%) in the supplemented steers. Choline concentration in rumen fluid and duodenal chyme were higher in the supplemented steers. Choline supplementation in Experiments 1 and 3 had no effect on rumen VFA or rumen pH. Dietary choline supplementation apparently is ineffective because of rapid degradation of choline in the rumen.