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After a brief survey of metabolic pathways and nutrient fluxes involved in mammary lipogenesis, this review summarises the known effects of diet on ruminant milk fat composition. Special attention is given to fatty acids that could play a positive role for human health, such as butyric acid, oleic acid, C18 to C22 polyunsaturated fatty acids and conjugated linoleic acid (CLA). 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 taken into account are the nature of forages, including pasture, and the supplementation of dairy rations with protected or unprotected vegetable or fish oils. Dose-response curves of milk CLA are reviewed for different fat supplements, as well as the non-linear relationship between milk CLA and trans C18:1. 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 aspects of milk fat quality. ruminant / nutrition / milk / fatty acids / human health Rsum -Plasticit de la matire grasse du lait de ruminant : contrle nutritionnel des acides gras saturs, polyinsaturs, trans et conjugus. Aprs un bref rappel des voies mtaboliques et des flux de nutriments qui concourrent la lipogense mammaire, cette revue est consacre aux principaux effets des facteurs alimentaires sur la composition des lipides du lait de ruminant. Un intrt particulier est port aux acides gras qui peuvent avoir des effets positifs sur la sant humaine, tels que les acides butyrique, olique, linolique conjugu (CLA) et les acides gras polyinsaturs, de 18 22 atomes de carbone. L'efficacit du transfert des C18:2, C18:3, C20:5, C22:5 et C22:6, du duodnum au lait est estime partir des donnes de la bibliographie. Les principaux facteurs alimentaires considrs sont la nature des fourrages, dont l'herbe pture, et la supplmentation des rations pour vaches laitires avec des huiles vgtales ou de poisson, protges ou non. L'augmentation potentielle
Chilliard et al. (Mon,) studied this question.