Ration Effects on Rumen Acids, Ketogenesis, and Milk Composition. II. Restricted Roughage Feeding

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Abstract
Four different types of concentrate (pelleted corn, ground corn, corn and cob meal, and herd mix) were fed with concentrate-to-roughage ratios of 3 to 1, 3 1/2 to 1, and 4 to 1. All rations decreased rumen acetate and increased propionate. Pelleted corn increased blood ketones. Some depression of milk fat percentage was also observed on all rations. Ranking the concentrates in the order of tendency to produce milk fat depression, based on changes in milk fat percentage and other associated changes, resulted in the following order: pelleted corn; ground corn; herd mix; corn and cob meal. The addition of 2% urea to the pelleted corn did not alleviate these effects. Sodium bicarbonate given by capsule caused some recovery of milk fat percentage, but reduced dry matter intake. At this level of concentrate feeding, the type of concentrate had a greater effect on rumen fermentation and accompanying changes than the concentrate-to-roughage ratios. There was little change in the ratio of rumen volatile fatty acid (VFA) as the ratio of concentrate to roughage was increased, except for butyric acid, which was higher at the lowest ratio.