Early in the 20th century, researchers found that fat-free diets had adverse effects on growth in rats. This newly discovered “factor” was suspected to be a vitamin which they labeled at the time vitamin F. It was later on that the unknown substance was identified not as a vitamin but a combination of essential unsaturated fatty acids (FA), with linoleic acid being the predominant one.
Since then, their effect on brain function, immune response and skin health has been documented extensively. The reason is: The body is unable to desaturate fatty acids beyond one double bond (oleic), making the presence of linoleic (two double bonds) and linolenic (three double bonds) essential in the diet of livestock and humans.
Modern research has found that under certain altered rumen environmental conditions in dairy cows, biohydrogenation of linoleic acid can follow alternate pathways which generate specific intermediaries, such as the trans-10, cis-12 conjugated linoleic acid (CLA) and trans-10 C18:1.
Once absorbed, these metabolites are carried to the mammary gland, where they reduce milkfat synthesis by interfering with the expression of genes that code lipogenic enzymes and key regulatory molecules. So, yes, polyunsaturated fatty acids are needed in the diet – and yes, under certain rumen fermentation conditions, too much will reduce the production of milkfat.
Continue reading this article published in Progressive Dairy