Occurrence of trans-Unsaturated Fatty Acids in Horse Fæces

Abstract

IT has been shown recently^1,2 that whereas the depot fats of ruminants contain considerable amounts of trans-unsaturated acids (3.5–11.2 per cent) the depot fats of non-ruminants contain but little or none. Since the rumen bacteria exhibit a pronounced hydrogenating effect³ and hydrogenation induces trans-isomerization, the occurrence of trans-acids in the fats of ruminants has been attributed by us to bacterial action^1,2. This hypothesis has now found additional support from the determination of the trans-acids content of horse fæces from pasture-fed animals. The lipids isolated from fresh fæces (6.66 per cent on the moisture-free basis) contained approximately 14 per cent of these acids determined by the infra-red absorption technique⁴ (Table 1), whereas no trans-acids could be detected in the depot fat of pasture-fed horses^1,2. In view of the fermentative bacterial flora in the large intestines, and the reducing atmosphere in these organs, the above result is not unexpected, and points to a mechanism of trans-acids formation similar to that in the rumen, but occurring in the post-absorptive region of the gut. The iodine value and the diene and triene contents of the fatty acids from the fæces, shown in Table 1, indicate also extensive hydrogenation when compared with the corresponding data for the depot fat of the horse⁵, and for pasture lipids⁶.