Effect of yeast, protected minerals and bismuth subsalicylate on in vitro fermentation by rumen microbes.

University of Minnesota Ph.D. dissertation. April 2012. Major: Animal science. Advisor: Dr Marshall D. Stern. 1 computer file (PDF); x, 192 pages.Three experiments were conducted using a dual flow continuous culture fermenter system. In Experiment I, two levels of active dry yeast at 0 or 2 mg/fermenter/day (NY and YS, respectively) were infused twice daily to fermenters in a completely randomized arrangement of treatments. Apparent and true OM digestion was not affected by yeast. No differences were obtained in NDF and ADF digestion. Total VFA concentrations were not affected by treatments. Addition of yeast did not affect VFA molar proportions or estimated CH4S production but resulted in a trend for a lower A:P ratio. Addition of yeast decreased NH3-N concentration and NH3-N daily flow, without affecting crude protein digestion and efficiency of microbial protein synthesis. Mean and minimum pH of fermenters did not differ between treatments but a trend for a lower maximum pH was obtained with yeast. In conclusion, a low dose of active dry yeast decreased NH3-N concentration and daily flow, without affecting any other of the in vitro rumen fermentation characteristics measured in this study. In Experiment II, effects of two levels of lignosulfonate and two sources of minerals (protected and unprotected) on rumen fermentation were evaluated using a 2 x 2 factorial arrangement of treatments. Addition of lignosulfonate tended to decrease daily flow of non NH3-N, efficiency of microbial protein synthesis, total VFA concentration and molar proportion of acetate, but increased molar proportion of propionate, valerate and caproate. Protected minerals decreased molar proportion of propionate. Addition of lignosulfonate increased ruminally soluble Cu and Mn, whereas protected minerals reduced ruminally soluble Cu. Concentrations of bacterial Cu and Zn increased with protected minerals in absence of lignosulfonate. Concentration of Mn was not affected by treatments. Addition of lignosulfonate resulted in higher enzymatic release of Zn from solids outflow but lower from bacterial pellets. Mean, minimum and maximum fermentation pH was higher with lignosulfonate, and not affected by mineral source. Addition of lignosulfonate induced major changes in ruminal fermentation. Protection of minerals decreased rumen soluble Cu and increased bacterial Cu and Zn without affecting postruminal release of minerals. In Experiment III, addition of bismuth subsalicylate (BSS) at 1% of DM and monensin (MON; 5 ppm) were used to assess their effects on rumen metabolism and H2S release by rumen microbes in a 2 x 2 factorial arrangement of treatments. Addition of BSS increased digestion of OM, NDF and ADF but decreased that of NFC and total VFA concentrations. Molar proportions of acetate and propionate increased with BSS in the diet, while that of butyrate decreased. Monensin decreased ADF digestion and A:P ratio, without affecting molar proportions of major VFA. Regarding nitrogen metabolism, MON increased non NH3-N outflow without affecting other measurements. Addition of BSS to the diet increased NH3-N concentration, NH3-N flow and dietary-N flow, while decreasing microbial-N outflow, CP digestion, and efficiency of microbial protein synthesis. Headspace H2S was reduced by 99% with BSS treatment but was not affected by MON. Only minor changes in fermentation pH were found with MON, but an increase in mean, minimum and maximum fermentation pH were found following addition of BSS. Results indicate that BSS can markedly reduce H2S production in short term and long term in vitro rumen incubations