Recently in vitro and in situ techniques have been used for assessing forage nutritive value for ruminants instead of laborious in vivo trials. Although, Blummel and Ørskov (1993) have shown that an in vitro gas production technique gives reliable estimates of forage nutritive value, whether the estimates could be correlated with in situ degradation are not well established. There is little known about the differences in degradation characteristics of neutral-detergent fibre (NDF) and cellular contents (CC: soluble carbohydrates, lipids and crude protein) in the rumen, and also about the relationships between component degradation rate in the rumen and gas production rate for different forages. This is because most in situ kinetic studies have followed the disappearance of insoluble cell wall constituents and comparative studies of in vitro and in situ estimates was not performed sufficiently.
The objective of this experiment was to investigate the relationship between in situ degradation of forage components and in vitro gas production rate for the three forages.