Effect of dietary lipid on the content of conjugated linoleic acid (CLA) in beef muscle

We have examined the effect of dietary fats containing n-3 polyunsaturated fatty acids on the conjugated linoleic acid (CLA) content of beef m. longis simus lumborum. Four groups of eight Charolais steers were given, for 120 d ays, grass silage plus a barley/sugar-beet feed concentrate containing one of four fat supplements: Megalac (saturated), linseed (high 18 : 3), fish o il (high 20 : 5 n-3, eicosapentenoic acid and 22 : 6 n-3, docosahexaenoic a cid) or linseed plus fish oil. The concentrates supplied 400 g/kg dry-matte r (DM) tintake and were designed to supply 45 g/kg of the total dietary fat calculated to be 60 g/kg of DM and to contain similar amounts of linoleic acid. Muscle from steers given the Megalac supplement contained 11.3 mg CLA per 100 g muscle and this was increased two- to three-fold in animals give n the more unsaturated fat supplements. The increased deposition of CLA was similar for both linseed and fish oil supplements although the concentrati ons of total n-3 polyunsaturated fatty acids in the fish oil diet were much less than in the linseed diet. This suggests potent inhibition of conversi on of CLA to trans vaccenic acid by fish oil fatty acids or their rumen met abolites.