Nutritional manipulation of the fatty acid composition of sheep meat: a review

Abstract

SUMMARYSheep meat is characterized as being high in saturated fatty acids and low in polyunsaturated fatty acids (PUFA), attributes that are regarded as being disadvantageous within the human diet. Despite fresh forage being a particularly rich source of 18:3n−3 and vegetable oils being high in 18:2n−6 and 18:3n−3, the process of biohydrogenation in the rumen generally results in proportionally less than 0·1 of these essential dietary fatty acids (FA) reaching the small intestine. Increases in muscle content of 18:3n−3 of 1–2-fold have been achieved by supplementation with oil, or oilseeds, whilst increases of 1–3-fold have been obtained from grazing grass compared with concentrates, but in general the polyunsaturated to saturated FA ratio (P:S) in sheep meat has remained low at approximately 0·2–0·3. Substantial improvements in the P:S ratio of up to 0·57 and increases in muscle and adipose tissue levels of 18:3n−3 of up to 4 g/100 g FA can be obtained, but rely on protecting dietary PUFA from biohydrogenation. Additionally, increasing tissue supply of 18:3n−3 will result in only a small improvement in muscle concentration of the nutritionally beneficial 20:5n−3 and 22:6n−3, with meaningful increases relying on a dietary supply of these very-long-chain PUFA. An alternative strategy to improve the human health attributes of sheep meat is to decrease tissue levels of 18:0 by increasing the activity of stearoyl-CoA desaturase (SCD), although the response is often relatively small. Despite the apparent negative impact of ruminal metabolism on muscle FA content, the process of biohydrogenation is often incomplete and several of the intermediaries can have positive effects on human health. Within these intermediaries, future increases in tissue content ofcis-9,trans-11 conjugated linoleic acid (CLA) may be obtained by increasing tissue supply directly, although a greater response may be obtained by maximizing tissue supply oftrans-11 18:1 and elevating the action of SCD. Production of a FA profile in sheep meat that is higher in PUFA, particularly the advantageous very-long-chain PUFA, and with flavour and eating characteristics that meet specific market preferences, is a suitable area for research.