DIGESTION AND UTILIZATION OF FATTY-ACIDS BY RUMINANTS

This review deals with the quantitative and qualitative changes in fat ty acids (FA) throughout the total digestive tract of ruminants. Speci al attention is paid to the causes of variation in the extent to which different mechanisms contribute to the ruminal metabolism and intesti nal digestion of FA. Most results obtained with diets not supplemented with lipids show that the FA flow leaving the rumen is higher than FA intake. This is due to bacterial synthesis of FA in the rumen. With d iets supplemented with lipids, the FA balance at the end of the rumen is often negative. The cause of this apparent disappearance of FA is n ot known. In the rumen, lipids are first hydrolysed to a very large ex tent; then unsaturated FA are hydrogenated. Hydrogenation is almost co mplete for linolenic acid, and amounts to between 60 and 95% for linol eic acid. This proportion decreases when the level of concentrates inc reases in the diet. Digestibility of FA in the small intestine ranges from 70 to 90% and is not related to the level of FA intake. Contrary to the situation in monogastric animals, there are only moderate diffe rences in the digestibility of individual FA. It appears to be higher for palmitic and stearic acids than for other saturated FA, and for ol eic and linoleic acids than for stearic and linolenic acids. In the la rge intestine, there is synthesis of FA which are probably not absorbe d.