Jennie's assertion that the biohydrogenation of PUFA by bacteria in
ruminant gut effectively prevents their incorporation into tissue
reflects older information which has now been supplanted by more recent
data.
        It has been recently shown (1) that ruminal bacteria have
limited ability to hydrogenate both 20:5n3  and 22:6n3, such that
enrichment of cattle feed by fish oil increases (3-4 fold) muscle
phospholipid concentrations of  20:5n3, 22:5n3 and 22:6n3, but not
adipose or muscle triglyceride levels of these fatty acids (1,2).
        More germane to our recent discussion is whether or not grass
fed cattle maintain differences in tissue fatty acid composition
compared to grain fed cattle.  There is substantial literature which
shows enhanced n3 fatty acid incorporation in both tissue phospholipids
and triglycerides of grass fed cattle when compared to grain fed cattle
(3,4,5,6,7).

                                REFERENCES

1.  Ashes JR et al.  Incorporation of n-3 fatty acids of fish oil into
tissue and serum lipids of ruminants. Lipids 1992;27:629-31.

2.  Mandell IB et al.  Effects of fish meal in beef cattle diets on
growth performance, carcass characteristics, and fatty acid composition
of longissimus muscle. J Anim Sci 1997;75:910-919.

3.  Mitchell GE et al.  Influence of feeding regimen on the sensory
qualities and fatty acid contents of beef steaks. J Food Sci
1991;56:1102-03.

4.  Hebeisen DF et al.  Increase concentrations of omega 3 fatty acids
in milk and platelet rich plasma of grass fed cows.  Intl J Vit Nutr Res
1993;63:229-33.

5.  Duckett SK et al.  Effects of time on feed on beef nutrient
composition. J Anim Sci 1993; 71:2079-88.

6.  Miller GJ et al.  Lipid characteristics in fresh and broiled loin
and round steaks from concentrate fed and pasture grazed steers. J Food
Sci 1987;52:526-29.

7.  Larick DK et al.  Flavour characteristics of forage and grain fed
beef as influenced by phospholipid and fatty acid compositional
differences. J Food Sci 1990;55:313-17.