Influence of Lactation Stage on Milk Yield and Milk Fatty Acid Profile in Dairy Ewes

Abstract. Our objective was to evaluation milk yield, milk components, and especially fatty acid profile of milk fat, in relation with stage of lactation. Sheep were kept indoor and were fed the same diet, which consisted of hay, corn silage and concentrate mix. Individual milk yields were recorded weekly over a two-month period. Effect of lactation stage was determined in weeks 2, 6, 10 and 14 after weaning of lambs. TU ewes yielded more milk, with a higher content of fat and protein, and milk fat had a lower content of saturated FA (C10:0, C12:0, C14:0) and a higher content of polyunsaturated FA, so that atherogenic index (AI) recorded the best value for this breed. We observed a strong correlation between milk fat trans-vaccenic acid (trans-11 C18:1-VA) and cis-9, trans-11 CLA on the one hand, and between cis-9, trans-11 CLA and ∆9 desaturase system on the other hand. Tzurcana breed also had the highest concentration of c9,t11-CLA in milk, which was due not only to an increase of VA supply in the rumen, but also to an increase in ∆9 desaturase enzyme activity. Milk n-3 FA content, mainly that in α-linolenic acid (ALA) was not influenced by breed. As lactation progressed, milk fatty acid profile changed in a positive way, as saturated FA content and the AI value decreased gradually, while ALA and c9,t11-CLA content increased. Use of Tzurcana breed for milk production or in breeding programs can be a way to improve milk fat and dairy product FA profile