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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:286920 |
| Date | January 1999 |
| Creators | Wachira, Ann Mumbi |
| Publisher | Open University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oro.open.ac.uk/58007/ |
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