Changes in the rumen bacterial community in response to sunflower oil and fish oil supplements in the diet of dairy sheep

Rumen microbial biohydrogenation of dietary unsaturated fatty acids has a major effect on the process of developing healthier dairy products. This study aimed to investigate in vivo the effect of diet supplementation with sunflower (SO) and fish (FO) oils on the rumen bacterial community in dairy sheep. First, 32 lactating ewes, divided in 8 lots of 4 animals each (2 lots per treatment), were fed a high-concentrate total mixed ration supplemented with 0, 2% SO, 1% FO, or 2% SO plus 1% FO. After 21 d, rumen fluid samples were taken from each lot for DNA extraction and fluorescence in situ hybridization (FISH) analysis. In a second experiment, 5 cannulated ewes were first fed the same TMR, with the exception of a higher forage level, and then changed to the same diet supplemented with 2% SO plus 1% FO. After 0, 3, and 10 d, rumen content samples were taken for DNA extraction and FISH analysis (fluid). Total bacteria and the Butyrivibrio group were studied in microbial DNA by terminal RFLP analysis (T-RFLP), and real-time PCR was used to quantify Butyrivibrio bacteria that produce vaccenic acid or stearic acid. In rumen fluid samples, total bacteria and clostridial clusters IX and XIV were analyzed by FISH. Dietary supplementation with SO plus FO seemed to induce important changes in the total bacteria and Butyrivibrio populations, and a high interindividual variation was observed, and the speed of the effect of the lipid supplementation depended on the individual microbial composition. Analysis by T-RFLP and FISH showed increases in cluster IX bacteria with SO plus FO supplementation, presumably Quinella-like microorganisms. The abundances of vaccenic acid- and stearic acid-producing Butyrivibrio relative to total bacteria, estimated by real time PCR, were low (0.28 and 0.18%, respectively, in rumen fluid, and 0.86 and 0.81% in rumen contents) and only that of SA-producing bacteria seemed to be reduced by diets containing FO, although differences were only significant in lactating ewes. The T-RFLP analysis showed a variable effect of lipid supplementation on different bacteria of the family Lachnospiraceae, which includes the cultured bacteria known to be actively involved in rumen biohydrogenation. These results suggest that the latter bacteria do not play a dominant role in this process, and therefore other as-yet-uncultivated microorganisms might be more relevant.