Que peut-on attendre des pratiques d'élevage pour améliorer la qualité nutritionnelle des matières grasses du lait bovin et caprin

This review gives an update of available data on the effect of nutrition on milk fatty acid (FA) composition in dairy cow and goat. It starts by an overview of the main digestive and metabolic pathways involved in the milk fat secretion processes. Used data are originated from literature and from two databases developed by INRA. Altogether, analyses confirm the wide plasticity of milk FA profiles in dairy ruminant, peculiarly for the saturated FA (10-18 carbon), oleic (9c-18:1) and vaccenic (11t-18:1) acids, and other trans isomers of 18:1 and 18:2. Comparing effects of diets with large amount of concentrate and/or maize silage with grass-based diets (grazed or correctly preserved) shows a decrease in saturated FA, at the expense of 9c- and 11t-18:1, and to a lesser extent, 18:3 n-3 and 9c11t-CLA. Dietary supplements of plant oil or oilseeds have similar effects, sometimes more marked, but they increase simultaneously other trans isomers of 18:1 and 18:2, especially when added to maize silage and/or high-concentrate diets. Oils or seeds rich in 18:2 n-6 (sunflower, soybean…) increase particularly 10t-18:1, and 10t12c-, 8t10c-, 7t9c- and 9t11c-CLA, whereas those rich in 18:3 n-3 (linseed) enhance notably 13t/14t-18:1, and 9ct12-, 9ct13- and 11tc15-18:2. When comparing goats' with cows' results, it seems that they are less sensitive to the 11t- to 10t- ruminal shift, thus explaining the good stability and the large magnitude of the responses of their milk 11t-18:1 and 9c11t-CLA content to lipid supplementation of high-concentrate diets. Furthermore, goats seem to respond better than cows to 18:3 n-3 rich supplements. Ongoing studies are evaluating the use of milk FA profile as biomarkers for the authentication of milk according to production zone and type of feeding, or to predict methane enteric emissions by dairy cows receiving oilseeds. Future studies should also integrate the expected progress of knowledge on the potential effects on consumers of the different major and minor FA found in standard or modified dairy products, as well as putative secondary effects of feeding conditions on sensory quality of dairy products and ruminant health.