Dietary and genetic influences on fatty acid composition of sheepmeat

Three experiments were carried out to investigate dietary and genetic factors influencing the n-3 polyunsaturated fatty acid content of sheepmeat. In the first experiment, four isoenergetic and iso-nitrogenous diets, based on dried grass with similar fat levels (60 g/kg OM) from different sources; Megalac (control), linseed (a-linolenic acid, CI8:3n-3), fish oil (eicosapentaenoic, C20:5n-3 and docosahexaenoic, C22:6n-3 acids) and linseed plus fish oil were fed to four rumen and duodenal cannulated sheep in a 4x4 Latin square design. Biohydrogenation of C 18:3n-3 was, 80-92 % in all diets, while that of C20:5n-3 and C22:6n-3 was 58-74 %. Dietary n-3 PUFA decreased microbial efficiency (p<0.05) measured using the total purine technique as a microbial marker, whilst fish oil depressed fibre digestion in the rumen (p<0.01). In experiment two, the same four diets were randomly allocated to 72 lambs from three breeds; Suffolk, Soayand Friesland blocked on live weight. Muscle fatty acid content was 2.4-2.8 % of tissue weight. Compared to the control diet, linseed doubled the quantity of CI8:3n-3 in muscle and increased levels of C20:5n-3 and C22:6n-3 by 0.5 (p<0.001). Fish oil alone increased C20:5n-3 and C22:6n-3 by 3-4 times (p<0.001), whilst the mixed diet resulted in n-3 PUFA levels intermediate between the linseed and fish oil diets. Soay lambs deposited more PUF A on the control diet than Suffolk or Friesland lambs (p