Diets containing high concentrations of fish oils (which have high concentrations of the n-3 polyunsaturated fatty acids, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)) or linseed oil (which has a high concentration of the n-3 polyunsaturated fatty acid ∝ linolenic acid (18:3n-3)) have been shown to decrease blood lipid concentrations compared to diets containing high concentrations of n-6 polyunsaturated fatty acids. Recent evidence also suggests that a reduction in the n-6:n-3 ratio of fatty acids in the human diet is likely to reduce thrombogenesis and the incidence of cardiovascular disease. In view of the importance of n-6:n-3 fatty acid ratio in food the effect of forage:concentrate ratio in the diet of beef cattle on n-6:n-3 ratio in beef has been examined.