The diagram below shows the pathway by which butyrate, taken up from the rumen fluid into the reticulo-rumen mucosal epithelial cells, is converted to acetoacetate and b-hydroxybutyrate.  These products are the ketone bodies; the same metabolites formed in liver from acetyl CoA under conditions of rapid lipid oxidation as occurs during hepatic ketogenesis.  You learned about this earlier in your curriculum in your study of adaptations to food deprivation in non-ruminant animals.