Addition of live yeasts in high concentrate diets for ruminants has been shown to help maintaining the ruminal pH above 6, which could enhance the microbial biohydrogenation of unsaturated dietary fatty acids. Moreover, yeasts improve the growth of Megasphera elsdenii, a bacteria which favors the trans-10 pathway of biohydrogenation. So the objective of this study was to investigate the effects of live yeasts (Saccharomyces cerevisiae) on the biohydrogenation in the rumen of dairy cows receiving a high concentrate diet without added fat.
Three ruminally fistulated lactating dairy cows were given three diets based on corn silage (control, control plus 0.5g/d or control plus 5.0g/d of Saccharomyces cerevisiae NCYC SC47), according to a Latin square design. Ruminal contents were sampled and liquid and solid phases were separated with a 0.25mm metal sieve. Fatty acids profiles were obtained by gas chromatography.
The two doses of yeast resulted in similar effects. Live yeast significantly decreased myristic and stearic acids proportions, and significantly increased oleic and linoleic acids proportions by 16 and 32% in the liquid and the solid phases, respectively. No significant effect was observed for other biohydrogenation intermediates, but the cis9,trans11-C18:2 tended (P = 0.154) to increase with the addition of yeasts, whereas trans10-C18:1 numerically decreased (P = 0.225).
These results suggested that live yeasts affect microbial activity, lowering the extent of biohydrogenation without shifting toward the trans-10 isomers pathway
