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<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.