The objective of this study was to evaluate the effects of Saccharomyces cerevisiae on in vitro gas production (GP) kinetics and degradability of corn stover, oat straw, sugarcane bagasse and sorghum straw. Feedstuffs were incubated with different doses of yeast [0, 4, 8 and 12 mg/g dry matter (DM)] at direct addition or 72 h pre-incubation. Rumen GP was recorded at 2, 4, 6, 8, 10, 12, 14, 24, 30, 48, 54 and 72 h of incubation. After 72 h, rumen pH and methane were determined and contents were filtrated for DM, neutral (NDF) and acid detergent fibre (ADF) degradability. Fibrous species×method of application×yeast interactions occurred (P<0.001) for all measured ruminal GP parameters and degradability. The direct addition or 72 h pre-incubation of S. cerevisiae with corn stover improved (P<0.05) GP and methane and decreased (P<0.05) the lag time (L) and NDF degradability (NDFD). The direct addition of S. cerevisiae to oat straw increased (P<0.05) rate of GP (c) and decreased (P<0.05) asymptotic GP (b). However, 72 h pre-incubation increased (P<0.05) c with linearly decreased b, DM degradability (DMD) and NDFD. Applying S. cerevisiae for 72 h pre-incubation decreased (P<0.001) methane emission. The direct addition or 72 h pre-incubation of S. cerevisiae to sorghum straw increased (P<0.05) b, c, L, DMD and NDFD. Overall, the effect of dose varied among different feedstuffs and different application methods. Results suggested that the direct addition of S. cerevisiae could support and improve ruminal fermentation of lowquality forages at 4 to 12 g/kg DM. © M.M.Y. Elghandour et al.
