Aharoni, Y., Agricultural Research Organization, Newe Ya'ar Experiment Station, Haifa Post 31999, Israel
Brosh, A., Agricultural Research Organization, Newe Ya'ar Experiment Station, Haifa Post 31999, Israel
Holzer, Z., Agricultural Research Organization, Newe Ya'ar Experiment Station, Haifa Post 31999, Israel

A multi-compartmental, double-marker model was developed, using numerical simulation techniques, to analyse faecal concentration curves of two markers simultaneously and to estimate both particulate and solute matter kinetics in the gastrointestinal tract, and either digestibility of the diet-when the intake is known, or faecal output-when the intake is unknown. The model was examined with the data of two experiments where Co-EDTA and Cr-mordanted-NDF were dosed simultaneously to calves and cows. Model estimations of digestibility and mean retention times are compared with the previously estimated parameters.