Lipids in herbage : their fate in the rumen of dairy cows and implications for milk quality

This chapter describes the fatty-acid profile of lipids in milk and herbage normally included in dairy diets. The next section deals with the possible effects of forage management on lipid intake in dairy cows. Then a detailed account is given of the fate of fatty acids in the rumen, showing that important microbial transactions occur through which unsaturated fatty acids become partly hydrogenated and are converted into intermediates, some of which exert important metabolic functions in the cow. When such intermediates are incorporated in and excreted with the milk, some are now considered to have beneficial effects on human health. In the last section examples are presented on how fatty-acid metabolism in dairy cows can and should be represented in terms of their fate in the rumen, their absorption and metabolic role in the intermediary metabolism and finally how rumen fatty-acid metabolism can be simulated in a mechanistic dynamic model.