The Rate of Passage of Digesta through the Gastrointestinal Tracts of Potoroine Marsupials: More Evidence about the Role of the Potoroine Foregut

Retention times of a particulate marker ($^{103}Ru-P$) and of a solute marker ($^{51}Cr$EDTA) were measured in the gastrointestinal tracts of three species of potoroine marsupials (small nocturnal macropodoids) who were fed grain-based diets containing variable concentrations of fiber. The observed distribution of retention times can be described by a general curve whose characteristics show a delay period, during which there is little or no excretion of marker, followed by a sharp rise to a peak concentration. After the peak, the curve falls exponentially. Thus, in the present experiments, while there was a difference of 8-10 h between the excretion of 5% and 50% of the markers, 30-50 h elapsed between the excretion of 50% and 95% and of 95% and 99%. The similarity of mean retention times (MRT) (25-30 h) of the two markers in the gastrointestinal tracts of potoroine marsupials contrasts with the marked separation of digesta phases in macropodids. The different patterns of digesta flow in the two groups w...