Managing Mediterranean pastures in order to enhance the level of beneficial fatty acids in sheep milk

This paper updates our knowledge on the effects of the botanical composition and management of Mediterranean pastures on the fatty acid composition of sheep milk and cheese. It focuses on the effects of the forage species and its phenological phase on: (i) the fatty acid profile of the forage, and (ii) the milk fatty acid composition. Here we refer specifically to putatively beneficial fatty acids (mono- and poly-unsaturated fatty acids (PUFA)), including conjugated linoleic acid (CLA, C18:2 c-9, t-11) and vaccenic acid (C18:1 t-11). A database was set up compiled from the results of various studies carried out by our research group and this was statistically analysed. Both the forage species (P < 0.05) and its phenological phase (P < 0.08) affected the content of linoleic acid, a precursor of CLA in the forage. The PUFA level in milk was higher in ewes grazing pure legumes and grass-legume mixtures than in those grazing pure grass pastures. When the pasture mixture also contained a daisy plant (Chrysanthemum coronarium), the CLA and vaccenic acid levels were even higher. Linoleic (C18:2; c-9, c-12) linolenic (C18:3; c-9, c-12, c-15) CLA (C18:2; c-9, t-11) and vaccenic acid (C18:1; t-11) levels in milk decreased from the vegetative (early-mid lactation) to the reproductive phase (late lactation). The Δ9 desaturase activity (estimate by C14:1/C14:0 ratio), which is involved in the conversion of vaccenic acid to CLA in the mammary gland, supports the hypothesis that the lower the substrate supply the higher the endogenous CLA synthesis. Finally, no marked differences were found in the fatty acid composition of milk and cheese from dairy sheep. Guidelines for managing the nutrition of grazing sheep to increase the unsaturated fatty acid content in milk are discussed.