Cow diets for healthier milk
Conjugated linoleic acid is formed in the rumen and mammary gland of cattle by the action of an enzyme stearoyl-CoA desaturase on a fatty acid. Needless to say, cow's milk forms a very significant part of our diet. The cow has the ability to synthesise conjugated linoleic acid (CLA) in the rumen and mammary gland. The overall aim of the European project BIOCLA then was to encourage the cow, through diet and general husbandry, to produce as much CLA as possible. Studies by project partners at MTT Agrifood Research in Finland examined the effects of two dietary supplements on the production of CLAs in milk. First, they studied the impact of fish oil that inhibits the hydrogenation of the necessary precursor fatty acids in the rumen. Secondly, selected plant oils were provided as a dietary supplement in order to see their effect on the passage of fatty acids from the rumen and the final fatty acid composition of milk. A combination of sunflower (SO), linseed (LO) and fish oil (FO) at different levels, were fed to the cattle in a basic diet of grass sileage and a group with no oil added acting as a control. The addition of oils in the diet affected intake and in the case of fish oil, reduced milk fat but not yield and milk protein. In the case of FO with sunflower or linseed oil, milk fat and protein and overall yield were reduced. Inclusion of oils significantly affected the composition of milk fatty acids. Interestingly, it was characterised by a reduction of fatty acids that are synthesised in the cow 'de novo', that is from simple molecules, not the conversion using the stearase enzyme. However, the milk fat CLA content is enhanced when fed on a sileage based diet with fish oil. Linseed oil increases concentration further but not when combined with sunflower oil. This investigation shows how important the relative amounts and type or oil supplement can be when inhibitory fish oils are used as a supplement. The results of this research would seem a significant step in making milk, an already healthy drink, even healthier.
