MEASUREMENT OF THE RATE OF PASSAGE IN RESTRICTED-FED RABBITS - EFFECTOF DIETARY CELL-WALL LEVEL ON THE TRANSIT OF FIBER PARTICLES OF DIFFERENT SIZES

Rate of passage measurements (RPM) of different cell wall (CW) particl e sizes (0.05 mm < S1 < 0.315 mm, 0.315 mm < S2 < 0.5 mm, 0.5 mm < S3 < 1 mm, S4 > 1 mm) were investigated in two groups of four adult rabbi ts fed on two diets differing in their level of lignocellulose (acid d etergent fibre, ADF): control (C) = 16.0% ADF; high (H) = 21.8% ADF. I n order to determine the specific effect of fibre level without an eff ect on intake, the diets were given in the same quantities (110 g day- 1). CW particles of each size class (S1-S4) were labelled with Ce-141. RPM were performed by following the faecal excretion of Ce-141 for 6 days. The total mean retention time (TMRT) of CW was slightly reduced when the level of ADF increased (under similar feed intake level), bei ng 30.2 h and 28.8 h for C and H groups, respectively. The retention t ime in the mixing compartment (RTM) or in the 'terminal component' (TC RT) was not affected by dietary ADF level (mean values of 23.4 h and 2 6.8 h, respectively). The higher TMRT of fine particles (32.2-36.6 h f or S1) compared with that of larger particles (25-29 h for S2-S4) were related to the anti-peristaltic activity of the proximal colon. Parti cles between 0.3 and 1 mm in size did not show any differential rate o f passage. That the transit time (TT) did not differ (mean of 7.0 h) b etween particle classes suggested that no particle segregation (betwee n S1 and S4) occurred in the small intestine and distal colon of the r abbit. In contrast, RTM increased from 20.6 h for S1 to 26.2 h for S4.