[Effect of dietary fiber content reduction on digestive transit in the rabbit. Comparison and validation of models fitted to fecal marker excretion kinetics].

The rate of passage (RP) in several digestive compartments was studied in 4 adult female rabbits cannulated at ileum, and receiving ad libitum 3 diets with decreasing fibre content (40, 30 and 22% NDF). The RP values in the whole digestive tract and between ileum and rectum were simultaneously measured by following the fecal kinetics of 2 markers (169Yb and 141Ce adsorbed on the NDF fraction of the diets) given as single doses. The mean retention time (MRT) in the whole tract provided by modelling methods (models: Grovum and Williams or Ellis) were similar to those obtained by reference method (numeric integration). MRT values in the caecum and the stomach were provided by models and were in good agreement with those deduced from reference measurements. Compared with the Ellis model, the Grovum and Williams model estimated more precisely the RP in tubular compartments (ie small intestine and distal colon); but the increasing part of the kinetics was better fitted using the Ellis model, particularly for low-fibre diets. The decrease in fibre intake (-50%) led to a 12 h increase (+72%) of the whole tract MRT, originating mainly from a 2-fold increase of ileo-rectal MRT. The MRT in the stomach decreased from 3 to 1 h, whereas the RP in the small intestine increased. Therefore, the oro-ileal MRT (mean 5 h) was not affected. A low dietary fibre induces a longer cecal MRT of large particles, without significant change for fine particles.