In vitro effect of Saccharomyces cerevisiae on the microbial rumen population and fermentative indicators

A random block design was used, with factorial arrangement, to determine the effect of the yeast Saccharomyces cerevisiae or its metabolic excretions on the microbial rumen population in in vitro conditions. Five treatments were evaluated: A) filtered rumen liquid (FRL) (control), B) filtered rumen liquid + culture medium (blank), C) filtered rumen liquid + culture medium inoculated with S. cerevisiae, D) filtered rumen liquid + pellet of centrifugation of the culture medium inoculated with S. cerevisiae, and E) filtered rumen liquid + supernatant of the centrifugation of the culture medium inoculated with S. cerevisiae. The inclusion of S. cerevisiae, whether in its culture medium or in the form of pellet, favored the development of total viable bacteria and cellulolytic (bacteria and fungi) populations. However, there was effect on the populations of protozoa. The pH was the highest in the control (7.12) and in the pellet (7.18). This coincides with the minimum values of SCFA (22.14 mmol/L and 27.83 mmol/L) obtained in the control and the pellet, respectively. The results indicated that the activating effect of the yeast is associated with the actions that the live cells may exert on the rumen ecosystem.