| Summary: | An in vitro gas production (GP) experiment, using equine faeces as the source of inoculum, was conducted to assess the effect of a yeast preparation (Saccharomyces cerevisiae) on the fermentation of high-temperature dried lucerne. The experiment was a factorial design consisting of six levels of yeast supplementation of high-temperature dried lucerne; 0 g yeast g−1 (L0—Control), 2 g yeast g−1 (L1), 4 g yeast g−1 (L2), 8 g yeast g−1 (L3), 16 g yeast g−1 (L4) and 40 g yeast g−1 (L5) herbage added at two time points; time 0 (inoculation) and at hour 14 of the incubation to 4 replicate bottles (5 × 2 × 4). Total GP increased significantly (P<0.01) at the highest level of yeast supplementation (L5; 188 ml) compared to the control (L0) and all other levels of yeast supplementation (averaging 177 ml). Rate parameter values, e.g. fractional rate of degradation (FRGP) and time taken to produce 50 or 95% of the total gas production (T50 and T95, respectively) were all significantly (P<0.05) decreased by the supplementation of lucerne with yeast. Dry matter loss (DML) also decreased significantly (P<0.01) with the addition of yeast to the lucerne (735 vs. 660 for L0 and L5, respectively). The pH increased significantly (P<0.001) with yeast supplementation; however, there was no effect of yeast supplementation on total volatile fatty acid (VFA) concentration or VFA molar proportions. In conclusion, the addition of yeast to lucerne appears significantly to reduce the extent (DML) and rate at which lucerne is degraded, which has important implications for the overall energy balance in equids.
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