Fatty acid composition and bacterial community changes in the rumen fluid of lactating sheep fed sunflower oil plus incremental levels of marine algae

Supplementation of ruminant diets with plant oils and marine lipids is an effective strategy for lowering saturated fatty acid (FA) content and increasing the concentration of cis-9,trans-11 conjugated linoleic acid and long-chain n-3 FA in ruminant milk. However, changes in populations of ruminal microorganisms associated with altered biohydrogenation of dietary unsaturated FA are not well characterized. Twenty-five lactating Assaf ewes were allocated at random to 1 of 5 treatments composed of dehydrated alfalfa hay and concentrates containing no additional lipid (control), or supplemented with 25 g of sunflower oil and 0 (SO), 8 (SOMA(1)), 16 (SOMA(2)), or 24 (SOMA(3)) g of marine algae/kg of diet dry matter. On d 28 on diet, samples of rumen fluid were collected for lipid analysis and microbial DNA extraction. Appearance and identification of biohydrogenation intermediates was determined based on complementary gas chromatography and Ag+-HPLC analysis of FA methyl esters. Total bacteria and the Butyrivibrio group were studied in microbial DNA by terminal RFLP analysis, and real-time PCR was used to quantify the known Butyrivibrio bacteria that produce trans-11 18:1 or 18:0. Dietary supplements of sunflower oil alone or in combination with marine algae altered the FA profile of rumen fluid, which was associated with changes in populations of specific bacteria. Inclusion of marine algae in diets containing sunflower oil resulted in the accumulation of trans 18:1 and 10-O-18:0 and a marked decrease in 18:0 concentrations in rumen fluid. At the highest levels of supplementation (SOMA(2) and SOMA(3)), marine algae also promoted a shift in ruminal biohydrogenation pathways toward the formation of trans-10 18:1 at the expense of trans-11 18:1. Changes in the concentration of biohydrogenation intermediates were not accompanied by significant variations in the abundance of known cultivated ruminal bacteria capable of hydrogenating unsaturated FA. However, certain bacterial groups detected by terminal RFLP (such as potentially uncultured Lachnospiraceae strains or Quinella-related bacteria) exhibited variations in their relative frequency consistent with a potential role in one or more metabolic pathways of biohydrogenation in the rumen.