Cis-15 intermediates of biohydrogenation in the duodenal flow of cows receiving linseed

Abstract

Duodenal samples from a previous experiment (Akraim et al., 2006) were reanalysed for determination of cis-15 intermediates of ruminal biohydrogenation (BH). Three dry Holstein cows fitted with a duodenal cannula received a diet with 14% (dry matter basis) raw linseed. C18 fatty acids (C18FA) represented 6.3% of dietary dry matter, and contained 57.8% of C18:3. After 18 days adaptation, on each cow, twelve samples of duodenal flow were taken over 3 days, composited, and analysed for FA composition. Cis-9,trans-11,cis-15C18:3 and trans-11,cis-15C18:2 (CLnA) were identified by GC-MS. The proportion of CLnA was low, in spite of the high C18:3 intake. The first step of C18:3 BH, isomerisation to CLnA, was extensive because the C18:3 proportion was 13.5 times lower in the duodenum than in the diet (Akraim et al., 2006). The extensive C18:3 BH and the low proportion of CLnA suggest a rapid ruminal reduction of this FA. The proportion of the product of this first reduction, trans-11,cis-15C18:2, was much higher than that of CLnA, but quite variable among cows. This suggests that the reduction of this FA was slower than that of CLnA, although this reduction is supposed to be due to a broad range of bacteria. According to responsible bacteria, this reduction can lead to trans-11C18:1, or cis-15C18:1 and trans-15C18:1. Cis-15C18:1 represented only half the proportion of trans-15C18:1, suggesting either a direct BH of trans-11,cis-15C18:2 to trans-15C18:1, or a rapid isomerisation of cis-15C18:1 to trans-15C18:1.