LAUSR

BACKGROUND To study if the effect on fermentation of yeasts added in ruminant diets can be improved, the effect of adding dry (DY) or pre-activated (AY) Saccharomyces cerevisiae compared to unsupplemented rumen fluid (CT), on barley grain or sugarbeet pulp was evaluated under in vitro high-concentrate fermentative conditions. Yeasts were pre-activated by culturing aerobically at 30°C for 24h. RESULTS In Experiment 1, AY showed a higher concentration than DY at 6h incubation (6.83 vs. 5.76 log cfu mL-1 ; P=0.007), differences disappearing at 12h. This was supported by higher gas production with AY, especially on sugarbeet pulp. In Experiment 2, incubation pH was 6.24 and 6.31 for barley and sugarbeet pulp at 8 h (P<0.05), but no effect was recorded at 24h (6.00 and 5.96; P>0.05). With sugarbeet pulp, gas production promoted by AY was the highest (P<0.05) in the first 8h of incubation. However, differences with barley were lower and only detected between AY and CT at 12h (P<0.05). Total VFA concentration at 8h followed the same trend, but no differences were detected on molar VFA profile or lactate concentration. Microbial diversity was more affected by the incubation series than by experimental treatments, and inocula including yeasts (AY, DY) did not differ to unsupplemented rumen liquid. CONCLUSIONS when pre-activated, concentration of S. cerevisiae was initially higher and resulted in higher gas volumes, more on a fibrous (sugarbeet pulp) than a starchy (barley) substrate. The response is apparently quantitative, since no major changes were detected on biodiversity or fermentation profile. This article is protected by copyright. All rights reserved.