Effects of Three Yeast Strains on In Vitro Rumen Fermentation of Corn Stover and a Total Mixed Ration

This study aimed to evaluate the effect of three yeast strains, Pichia guilliermondii (Levica 27), Candida norvegensis (Levazoot 15), and a commercial product (Levucell® SC 10) containing Saccharomyces cerevisiae, on in vitro rumen fermentation of two substrates: corn stover and a total mixed ration (TMR). Samples were taken 24 hours post-fermentation to measure pH, ammonia nitrogen (NH3-N), gas production, and volatile fatty acid (VFA) concentrations. The addition of yeasts did not affect gas production at 24 hours for either diet. For pH, differences between yeast strains were noted when TMR was used. The lowest NH3-N concentration (6.1 mM) was recorded with corn stover, showing similar results across strains. Conversely, NH3-N levels with TMR ranged from 47 mM to 66 mM. The inclusion of all three yeast strains increased the molar concentrations of total VFA, as well as acetic (C2), propionic (C3), and butyric (C4) acids in the rumen fluid. The C2:C3 ratio remained unchanged with corn stover but decreased with the inclusion of Levica 27 and Levazoot 15 in the TMR. With the commercial product Levucell® SC 10, this ratio was comparable to the control treatment. In conclusion, Levica 27 and Levazoot 15 demonstrated a stimulatory effect on in vitro rumen fermentation for the evaluated diets, evidenced by increased VFA concentrations.