Ration Effects on Rumen Acids, Ketogenesis, and Milk Composition. I. Unrestricted Roughage Feeding

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Abstract
Two trials , with 12 cows each, using a 56 day comparison period were used to investigate the effect of feeding on rumen volatile fatty acids, blood ketone and sugar levels, and milk production and composition. In both trials, rations containing pelleted hay or pelleted corn produced the following changes: (1) Lower milk fat test. (2) Increased blood sugar levels. (3) Lower percentage of rumen acetic acid. (4) Higher percentage of rumen propionic acid. (5) Increased total concentration of rumen acids. This study suggests that on a weight basis a 1:3 propionate/acetate ratio would result in a normal test, a 1:2 ratio a definite depression, while a 1:2.5 ratio would be borderline. The feeding of pelleted corn tended to increase blood ketone bodies while feeding pelleted hay reduced them. An increase in total rumen acids with more butyrate to be metabolized would suggest butyrate to be the ketogenic agent. The high ketone levels did not prevent depression of milk fat test.