Dietary fish oil supplements modify ruminal biohydrogenation, alter the flow of fatty acids at the omasum, and induce changes in the ruminal Butyrivibrio population in lactating cows.

ABSTRACT

Four lactating cows fitted with ruminal cannulae and fed a grass silage-based diet were used in a 4 × 4 Latin square with 28-d periods to investigate the effects of incremental dietary fish oil (FO) supplementation (0, 75, 150, or 300 g/d) on the flow of fatty acids at the omasum and populations of rumen bacteria capable of biohydrogenation. FO decreased silage intake and ruminal volatile fatty acid concentrations and promoted an increase in molar butyrate and propionate proportions at the expense of acetate. Extensive ruminal biohydrogenation of 205(n-3) and 226(n-3) resulted in corresponding increases in numerous 20- and 22-carbon unsaturated fatty acids at the omasum. Omasal flow of several 20-, 21-, and 22-carbon all-cis (n-3) PUFA exceeded the intake from FO. Supplements of FO also induced a dose-dependent decrease in 180 and increased trans 181 and trans 182 flow at the omasum. Trans-11 was the major 181 intermediate in digesta, while FO induced quadratic increases in trans-10 181 flow, reaching a maximum of 300 g/d. FO had no substantial influence on omasal flow of CLA. Results suggest that one or more fatty acids in FO inhibit the reduction of trans-181 and trans-182 intermediates by ruminal microorganisms. qPCR based on 16S rRNA genes in omasal digesta indicated that key Butyrivibrio spp. declined linearly in response to FO. Dose-dependent increases in ruminal outflow of biohydrogenation intermediates containing one or more trans double bonds in response to FO has major implications for host metabolism and the nutritional quality of ruminant foods.