Modeling gas production kinetics of grass silages incubated with buffered ruminal fluid1

Time course measurements of in vitro gas production of feedstuffs incubated with buffered ruminal fluid give information about the rate at which the feed is fermented. To compare gas production kinetics from different feeds, a mathematical model was needed to describe the data. We investigated several existing models (exponential, logistic, Gompertz, Richards, Schnute), fitting them to 50 gas production curves obtained with grass silages. None of them gave a satisfactory description of the data. A new model was developed (modified Gompertz model; mGom) that basically divided gas production into two fractions, one arising from rapidly fermentable feed components and the other from slowly fermentable feed components. Residual mean squares (RMS) for the mGom model were lower (P < .05; n = 50) than the RMS for the other models. A good statistical comparison of kinetic gas production data is made possible with the mGom model.