Comparison of in vitro degradation of temperate forages production and filter using the gas bag techniques

BACKGROUND: Two of the most promising in vitro techniques for dynamic forage evaluation are the gas production (GP) and filter bag (FB) techniques. To improve our understanding of how these techniques describe the dynamic degradation of forages, 20 temperate forage samples were analysed by each method at different time points during a 96 h incubation period. The results of the recordings were fitted to a biphasic Michaelis-Menten model describing the degradation of rapidly and slowly degrading forage fractions. RESULTS: GP and disappearance from the FB measurements were correlated at all time points from 6 to 96 h (R-2 = 0.27-0.74), except at the 24 h incubation point. When GP was transformed into organic matter degradation (OMD), there was an even stronger correlation (R-2 = 0.54-0.75) between the techniques at all intervals. Comparison of the parameters from the Michaelis-Menten model resulted in correlations (R-2 = 0.83) between the sizes of the estimated forage fractions, but not between parameter determining the rates of their degradation. CONCLUSIONS: Both the GP and FB techniques have the potential to estimate the degradation of individual feed fractions in forages. Further studies in which the in vitro parameters are evaluated against livestock data, are needed to confirm the findings of this study, however. (c) 2007 Society of Chemical Industry.