Evaluation of different methods for the determination of digestion and passage rates of fibre in the rumen of dairy cows

Ruminai digestion and passage rates and digestibility of NDF were measured in vivo with four cannulated dairy cows in early lactation in a 4 x 4 Latin square design. In vivo rates of digestion and passage were determined using the rumen evacuation technique. Rumen digestion characteristics of NDF were also determined using the in sacco technique, and passage rate of Yb‐labelled feed particles was determined by fitting various one‐ and two‐compartment models to Yb concentrations in duodenal digesta. Digestion rates and mean retention times determined by the indirect methods were compared with those determined by the rumen evacuation technique. Digestion and passage rates were also evaluated, based on their ability to estimate the observed rumen in vivo NDF digestibility when combined.