Evaluation of in vitro gas production of high starch diets supplemented with live yeast in dairy cows

The purpose of this study was to evaluate the effects of adding Saccharomyces cerevisiae as live yeast (LY) to a high-starch total mixed ration on in vitro gas production, some ruminal fermentation parameters and organic matter (OM) digestibility. This experimental study was conducted in a 2 × 2 factorial design with two levels of starch (23% and 33% of dietary DM) and two doses of LY (0 and 2.9 × 106 cfu/200 mg substrate DM) resulting in four treatments. Treatments were adequate starch (AS) and no LY (AS-control); AS with LY (AS-YC); high starch (HS) and no LY (HS-control), and HS with LY (HS-YC). LY was added to diets at 2.9 × 106 cfu/200 mg DM. Rumen gas production was recorded after 3, 6, 9, 12 and 24 h of incubation. At the end of the incubation period, pH and CH4 were determined. OM digestibility, ME, total short chain fatty acids (SCFA) were calculated at 24 hours of incubation. Gas production at 3, 6, 9, 12 and 24 h of incubation was not affected by either the supplementation of LY or the proportion of starch in the diet. The proportion of starch in the diet, the supplementation of LY, and their interaction did not affect diet the fermentation parameters, ME and CH4. In conclusion, in this study, when the in vitro gas production parameters, digestibility and fermentation properties were evaluated as a whole, no beneficial effect of S. cerevisiae on ruminal fermentation and digestibility was detected, added to the corn-based high starch dairy cattle rations. Therefore, further studies are needed to evaluate the response of diets with different starch sources and levels to the addition of live yeast S. cerevisiae. Key words: Live yeast, Gase production, Dairy cow, Diets containing high starch