Comparison of in vitro gas production technique with in situ nylon bag technique to estimate dry matter degradation

Dry matter (DM) degradation of wheat straw (WS), barley straw (BS), lucerne hay (LH) and maize silage (MS) was determined using two different techniques: (i) in vitro gas production and (ii) nylon bag degradability technique. In vitro gas production and in situ DM disappearance were measured after 3, 6, 12, 24, 48, 72 and 96 hours of incubation. In situ and in vitro DM degradation kinetics was described using the equation y = a + b (1 – ect). In all incubations there were significant (P < 0.001) correlations between gas production and in situ DM disappearance or estimated parameters ((a + b)gas and (a + b)is or (a + b)gas and EDMDis) whereas there were no significant (P > 0.05) correlations between cgas and cis or bgas and bis. Gas production from the insoluble fraction (b) alone explained 98.3% of the variation of EDMD. The inclusion of gas production from the quickly soluble fraction (a) and rate constant (c) of gas production in the regression equation improved the accuracy of EDMD prediction. The correlations between the results of both methodologies seem to be sufficiently strong to predict degradability parameters from gas production parameters. It was concluded that the in vitro gas production technique has good potentiality to predict in situ DM disappearance and some DM degradation parameters.