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 non-CO2-saturated buffer at inoculation. Vessel type (50-ml polypropylene tube, 125-ml 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 125-ml Erlenmeyer flasks resulted in faster rates of NDF digestion than CO2-saturated buffer in 50-ml screw-cap 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.