Δ9 desaturase protein expression and fatty acid composition of longissimus dorsi muscle in lambs fed green herbage or concentrate with or without added tannins

The aims of this study were to investigate the effect of feeding system and of supplementation of tannins (8.93% DM) on the relationship between intramuscular fat content, fatty acid composition and Δ9desaturase (Δ9d) protein expression in longissimus dorsi muscle of lamb. Twenty-eight Comisana lambs (age 45 days) were fed either vetch (Vicia sativa) or concentrate. The herbage diet was (i) lower in saturated fatty acids (especially in C16:0), C18:1 n−9 and in C18:2 n−6; (ii) higher in C16:1 and C18:3 n−3 when compared to concentrate. Within each feeding system the lambs were divided into two sub-groups, one of which received the diet without tannins supplementation, and the other was fed the diets supplemented with the tannins from Quebracho (Schinopsis lorentzii). The animals were slaughtered at age 105 days. The concentrate feeding system increased (p < 0.01) the total intramuscular fat content and the amount of SFA, MUFA and n−6 PUFA and decreased the level of n−3 PUFA (p = 0.05) when compared to the vetch-fed animals but did not affect Δ9 desaturase protein expression. There was no correlation between Δ9d protein expression and total intramuscular fatty acids, CLA and MUFA level. It was suggested that in ruminants, in contrast to monogastric animals, Δ9d expression does not play the key role in intramuscular fatty acids formation. Tannins supplementation resulted in higher (p < 0.05) muscle levels of transC18:1 and C18:2 n−6. It has also increased Δ9d expression in the case of herbage-based diet but not in the case of concentrate-based diet. The mechanism of tannins action on the enzyme expression needs to be elucidated.