EVALUATION OF DIFFERENT METHODS FOR THE DETERMINATION OF DIGESTION AND PASSAGE RATES OF FIBER IN THE RUMEN OF DAIRY-COWS

Ruminal digestion and passage rates and digestibility of NDF were meas ured 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 chara cteristics of NDF were also determined using the in sacco technique, a nd passage rate of Yb-labelled feed particles was determined by fittin g various one- and two-compartment models to Yb concentrations in duod enal digesta. Digestion rates and mean retention times determined by t he indirect methods were compared with those determined by the rumen e vacuation technique. Digestion and passage rates were also evaluated, based on their ability to estimate the observed rumen in vivo NDF dige stibility when combined.