This study investigated the effects of dietary n-3 polyunsaturated fatty acids (PUFA) on muscle fatty acid composition and content in two cattle breeds; the Holstein-Friesian, a dairy breed, and the Welsh Black, a traditional beef breed. Animals were kept on ad libitum grass silage and one of three concentrates varying in the source of fat; Megalac (high in C16: 0),formaldehyde treated whole linseed (high in C18: 3 n-3) and a combination of formaldehyde treated whole linseed and fish oil (high in C20 : 5 n-3 and C22 : 6 n-3). The concentrates were offered at approximately 0.4 of total dry matter intake. Samples of m. longissimus thoracis from Holstein-Friesians contained higher fetal amounts of fatty acids (P < 0.05) than that of Welsh Blacks in neutral lipid, hut the phospholipid fatty acid content was similar between the breeds. Over all treatments, the proportion of C18 : 3 n-3 was higher (P < 0.001) in muscle neutral lipid of Welsh Blacks and the proportions of C18 : 3 n-3 and C18 : 1 trans were higher (P < 0.05 and P < 0.001, respectively) in their subcutaneous adipose tissue. Feeding linseed increased the amounts of C18 : 3 n-3 and also C20 : 5 n-3 in muscle phospholipids suggesting chain elongation and desaturation of C18 : 3 n-3 had occurred. The concentration of C20 : 5 n-3 was significantly higher (P < 0.05) in muscle phospholipids of Welsh Blacks while no differences wen found for C18 : 3 n-3 and C22 : 6 n-3. However, when expressed as a proportion of total fatty acids, both C20 : 5 n-3 and C18 : 3 n-3 were significantly higher (P < 0.001) in the Welsh Black phospholipids. These differences resulted in a significantly higher P : S ratio of the muscle total fat (P < 0.05) in the Welsh Black than in the Holstein-Friesian but P : S was not affected by diet. On the other hand, the n-6 : n-3 PUFA ratio was significantly lower in the Welsh Black, reflecting the higher n-3 PUFA content. This ratio was lower in the linseed and the mixed treatments for both breeds, reflecting higher delivery of n-3 PUFA from these diets. Fortification of the diet with sources of PUFA and exploiting breed differences offer the potential to develop systems to increase human intakes of n-3 PUFA in line with current nutritional recommendations.
