Relationships between chemical composition, dry matter degradation and in vitro gas production of several ruminant feeds

Thirty-eight samples of 12 feedstuffs were used to study relationships between in vitro true digestibility of dry matter (IVTD) and in vitro gas production. Influences of chemical constituents on gas and volatile fatty acid (VFA) production were investigated. There was a negative (P<0.001) correlation between the CP content of feeds and in vitro gas production at 24 and 48 h incubation. Strong negative correlations also occurred between CP content and potential gas production. However, neither CP nor NDF level was correlated with rate of gas production and there was a poor correlation between IVTD and gas production. Non-fiber carbohydrate (NFC) level was positively correlated with potential gas production and gas production at 6 h (P<0.05), 24 h (P<0.001) and 48 h (P<0.001) of incubation. There was strong positive correlation (P<0.001) between CP level and isovalerate and valerate production. In vitro gas production at 24 h was positively correlated (P<0.001) with total VFA production. However gas production at 24 h was negatively correlated (P<0.05) with isovalerate and valerate production. Stepwise linear regression indicated that prediction of VFA from gas production at 24 h was improved by inclusion of feed CP level. Prediction of IVTD from gas production was sharply improved by inclusion of CP, NFC and fat levels to the regression. The chemical composition of feeds are important in accurately predicting IVTD and VFA production from in vitro gas production.