PSXII-30 - Effect of yeast strains on in vitro ruminal fermentation using different substrates.

Abstract: With the aim of evaluating the effect of the yeast strains Pichia guilliermondii (Levica 27), Candida norvegensis (Levazoot 15), and a commercial product with Saccharomyces cerevisiae (Levucell SC-10) on in vitro ruminal fermentation of two substrates (corn stover and a total mixed ration TMR), a completely randomized design with a 4 x 2 factorial arrangement and four replicates was used. Samples were taken at 24 h of fermentation, and pH, ammonia nitrogen (NH₃ -N), gas production, and volatile fatty acids (VFA) concentration were determined. The addition of yeast had no effect on gas production at 24 h in either of the two diets. There was no interaction between diets and yeast in pH, but differences between strains were obtained when using the total mixed ration (TMR). Interaction between yeast strains and diets was observed when analyzing NH₃-N levels. The lowest molar concentration was obtained with corn stover (6.1 mM) and was similar among strains with this substrate. However, with TMR, this variable increased to values between 47 mM and 66 mM. The inclusion of the three yeast strains increased the molar concentration of total VFAs, acetic, propionic, and butyric acids in the rumen fluid. The C2:C3 ratio remained unchanged when using corn stover and decreased with the inclusion of strains Levica 27 and Levazoot 15 in the TMR. In the case of the commercial product Levucell SC-10, this ratio remained similar to the control treatment. It is concluded that Levica 27 and Levazoot 15 had a stimulating effect on in vitro ruminal fermentation of the evaluated diets since they increased the molar concentrations of VFAs, results that should be considered in future in vivo studies with these strains.