Ruminant adipose tissue differs from that of monogastric species in having a high proportion of saturated fatty acids which gives it a high melting point. This difference results from the hydrogenating action of bacteria in the rumen which convert a high proportion of the dietary polyunsaturated fatty acids (PUFA) of forage and cereals into saturated fatty acids or unsaturated fatty acids with fewer double bonds, some of which are in the trans configuration. Although the ruminant is well adapted to this pattern of fatty acids for humans the consumption of such fat is nutritionally undesirable and in the case of lamb fat, organoleptically unsatisfactory since the lipid may congeal in the mouth. Any procedures to manipulate the fatty acid composition of ruminant lipids must reduce or avoid the. hydrogenation in the rumen.