Dietary and genetic influences on fatty acid composition of sheepmeat

Wachira, Ann Mumbi (1999). Dietary and genetic influences on fatty acid composition of sheepmeat. PhD thesis The Open University.



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<0.05). In the third experiment three iso-energetic and iso-nitrogenous diets, with different fat sources, Megalac or formaldehyde treated linseed (protected) with or without fish oil, and with two levels of vitamin E 100 (low) and 500 (high) mg/kg OM were randomly allocated to 96 lambs from two breeds; Suffolk and Scottish Blackface blocked on live weight. Muscle fatty acid content was 2.3-3.1 % of tissue weight but was lower in control fed lambs (p3 mg/kg muscle) in all lambs fed any of the diets. Overall, dietary modifications were more effective than genetic factors in increasing the n-3 PUF A in sheepmeat.

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