Designing milk fat to improve healthfulness and functional properties of dairy products: from feeding strategies to a genetic approach

The present review, in the first part, deals with the most effective feeding strategies applied to dairy ruminants in order to enhance the healthfulness of milk fat. The largest changes in milk fatty acid (FA) composition have been obtained either by changing the amounts and the nature of forages in the diets of ruminants, particularly pasture, or by adding plant or marine oils to the diet. Alpine and legume based pastures are associated with high levels of conjugated linoleic acid (CLA), omega-3 FA and with low levels of saturated FA, but further studies are needed with the aim to better explain the effect of some plant species on milk FA composition. Linseed, soybeans safflower and sunflower are the most effective sources of unsaturated plant lipids used to enhance CLA and unsaturated FA content in milk fat. Among animal sources, marine oil is more effective than plant oils for enhancing CLA, vaccenic acid (VA) and omega-3 FA in milk fat, especially when fish oil is fed in combination with oil supplements rich in linoleic acid. In the second part of the review the potential contribute of genetic improvement to modifying milk FA composition is discussed. Recent studies have suggested that the genetic improvement of the nutritional quality of milk based on FA profile may be possible. At this aim, genetic parameters of milk FA composition have been estimated in Dutch, US and Italian Holstein populations and in a Belgian multiple breed population of dairy cows. In dairy sheep and goat there is still a lack of knowledge about genetic parameters and correlations of milk FA. The develop of specific selection indexes aimed to improve the nutritional properties of milk could be supported by the new insight about potential candidate genes able to affect a significant quote of the milk FA variability. Increasing evidences indicate the Stearoyl-CoA Desaturase (SCD) and Diacylglycerol acyltransferase (DGAT-1) genes as possible sources of FA variation in milk. Evidences from quantitative and molecular studies suggest a potential future animal selection, but some question about the kind of selection mechanism and the economic incentive for the improvement should be preliminarily answere