impact of in vitro fermentation techniques upon kinetics of fiber digestion three in vitro fermentation experiments were conducted to examine the impact on kinetics of fiber digestion of microminerals and tryptone addition media reduction fermentation vessel co2 gassing regimen and buffer type alfalfa and bromegrass hays were incubated for 0 4 8 12 18 24 30 36 48 72 and 96 h and analyzed for ndf kinetic measures of fiber digestion were estimated using nonlinear regression with iteratively reweighted least squares in experiment 1 continuous co2 gassing increased rate and decreased lag time prior to ndf digestion compared with purging a nonco2saturated buffer at inoculation vessel type 50ml polypropylene tube 125ml pyrex erlenmeyer flask use of additives microminerals tryptone and media reduction had no effect on kinetics of ndf digestion in experiment 2 elimination of both media reduction and nutritive additives increased the lag time prior to ndf digestion in experiment 3 continuous co2 gassing of buffer in 125ml erlenmeyer flasks resulted in faster rates of ndf digestion than co2saturated buffer in 50ml screwcap polypropylene tubes the method that yielded the fastest rates and shortest lag times of ndf digestion consisted of continuous co2 gassing reduction and use of additives to ensure that no nutrient limited fiber digestion