INFLUENCE OF YEAST CULTURE ON THE INVITRO FERMENTATION (RUSITEC) OF DIETS CONTAINING VARIABLE PORTIONS OF CONCENTRATES

Incubation trials were carried out with the rumen simulation technique Rusitec to study the effects of a yeast culture (YC) from Saccharomyces cerevisiae on the fermentation of three different diets. The diets, having a forage:concentrate ratio (dry matter (DM) basis) of 70:30 (low-concentrate diet), 50:50 (medium-concentrate diet) and 30:70 (high-concentrate diet), were each incubated either with or without yeast culture (15 mg YC g-1 DM). Overall, the addition of YC had only a small influence on the fermentation parameters with the low-concentrate diet. Molar proportions of volatile fatly acids (VFA), however, were significantly affected (P<0.05). When the medium-concentrate diet was supplemented with YC, methane production (P<0.06), protozoal concentration (P<0.03) and acetate concentration (P<0.01) were reduced, while butyrate and valerate concentrations were increased (P<0.01). However, the degradability of DM and neutral detergent fibre (NDF), output of ammonia and microbial nitrogen synthesis were not affected (P>0.10) by the addition of YC. Adding YC to the high-concentrate diet increased DM and NDF degradabilities (P<0.01), VFA production (P<0.05), methane production (P<0.07) and the concentration of protozoa (P<0.02). On the other hand, the output of ammonia was reduced (P<0.10). These results indicate that YC influenced the rumen population and had a diet-dependent effect on the fermentation pattern.