Nominal response of passage rates to fiber particle size in rats

The influence of wheat bran particle size on the rate of passage of digesta through the rat gut was investigated. Small and large particle size wheat bran-supplemented diets were used in combination with the particulate digestion marker chromium mordanted bran (CrMB) and the soluble digestion marker cobalt-EDTA (Co EDTA). The particle size of CrMB did not significantly affect the estimates of marker residence halftime (t 1/2), mean retention time or transit time, when administered to animals fed a large particle bran diet. Utilization of different particle size bran diets and a common small particle CrMB marker tended to result in a longer t 1/2 and mean retention time in the smaller particle bran diet. Therefore, the selection of dietary particle size, but not CrMB particle size, tended to influence the estimates of t 1/2 and mean retention time. Similarly, the Co EDTA t 1/2, mean retention time and transit time tended to be longer in small particle bran-fed animals than in large particle bran-fed animals. In some comparisons the mean retention time of Co EDTA was significantly less (P less than 0.05) than that of CrMB, indicating that preferential retention of particles relative to solutes can occur in rats. Nevertheless, the overall movement of the liquid and particles largely corresponded.