Ruminant milk fat plasticity: nutritional control of saturated, polyunsaturated, trans and conjugated fatty acids

After a brief survey of metabolic pathways and nutrient fluxes involved in mammary lipogenesis, this review summarises the known effects of diet on ru minant mirk fat composition. Special attention is given to fatty acids that could play a positive role for human health, such as butyric acid, oleic a cid, C18 to C22 polyunsaturated fatty acids and conjugated linoleic acid (C LA). The efficiency of the transfer of C18:2, C18:3, C20:5, C22:5 and C22:6 , from the duodenum to the milk, is reviewed. The main dietary factors take n into account are the nature of forages, including pasture, and the supple mentation of dairy rations with protected or unprotected vegetable or fish oils. Dose-response curves of milk CLA are reviewed for different fat suppl ements, as well as the non-linear relationship between mirk CLA and trans C 18:1. The potential of dietary factors to increase the mean CLA content in cow milk fat is about 300% above basal values. There is, however. a need to evaluate how the different feeding strategies could change the other aspec ts of milli fat quality.