title: Estimating the extent of degradation of ruminant feeds from a description of their gas production profiles observed in vitro: comparison of models.
abstract: An evaluation of general models that describe gas production profiles is presented. The models are derived from first principles by considering a simple three-pool scheme and permit the extent of ruminal degradation to be calculated, as described in the companion paper. The models evaluated were the generalized Mitscherlich, simple Mitscherlich, generalized Michaelis-Menten, simple Michaelis-Menten, Gompertz, and logistic. Five sets of gas production data consisting of 216 curves, obtained using a wide range of feeds (including straw, hay, silage, grain and various byproducts), were analysed to study the performance of these gas production models. Application of the non-sigmoidal models (simple Mitscherlich and Michaelis-Menten) to the data resulted in convergence problems and these models were found to be inadequate in many cases. Based on results of a pairwise comparison between models (variance ratio test), ranking of residual mean squares, lack-of-fit test, and of analyses of residuals, the generalized Mitscherlich and the generalized Michaelis-Menten models seemed particularly suited because of their flexibility to encompass sigmoidal and non-sigmoidal shapes of gas production profiles, whether symmetrical or not.
authors.affiliation: Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, UK.
authors.forename: M S
authors.initials: MS
authors.lastname: Dhanoa
authors.forename: S
authors.initials: S
authors.lastname: Lopez
authors.forename: J
authors.initials: J
authors.lastname: Dijkstra
authors.forename: D R
authors.initials: DR
authors.lastname: Davies
authors.forename: R
authors.initials: R
authors.lastname: Sanderson
authors.forename: B A
authors.initials: BA
authors.lastname: Williams
authors.forename: Z
authors.initials: Z
authors.lastname: Sileshi
authors.forename: J
authors.initials: J
authors.lastname: France
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D005285:Fermentation; D005740:Gases / Q000032:analysis*; D016013:Likelihood Functions; D008432:Mathematical Computing; D012418:Ruminants
chemical_list: D005740:Gases