Reticulo-rumen biohydrogenation and the enrichment of ruminant edible products with linoleic acid conjugated isomers

Conjugated linoleic acid (CLA) is presently under extensive research because of its potent anticarcinogenic effects and also because of its effects on the immune system and on lipid metabolism. The biological effects of these acids are briefly reviewed. Ruminant edible products are the richest natural sources of CLA because they are supposed to be mainly derived from rumen biohydrogenation of linoleic acid. The end product of the main and more effective linoleic acid biohydrogenation pathway is the trans-11 C18:1. The contents of CLA and trans C18:1 acids are positively correlated in rumen contents, fat depots and milk, although their ratio (trans C18:1 /CLA) varies. Nutritional strategies for the enrichment of ruminant products with CLA will currently be achieved by increasing the supply of linoleic acid in reticulo-rumen metabolism, although this will also result in an increase in trans-11 C18:1. The inclusion in the diet of soybean oil up to 12% does not greatly affect the trans C18:1 /CLA ratio. The potential deleterious effects of trans octadecenoic acids on human health have been considered even if no consensus is reached. Therefore it will be important to manipulate rumen biohydrogenation in order to increase CLA output with a low trans C18:1 /CLA ratio. Although further investigation is needed, scarce data already suggest this could be achieved by increasing the supply of linoleic rich fat and modifying the basal diet or include ionophores.  2000 Elsevier Science B.V. All rights reserved.