DIETARY CELLULOSE IN THE GROWING RABBIT . 1. CONSEQUENCES ON DIGESTION AND RATE OF PASSAGE

The effect of the level and botanical origin of the dietary cellulose VS (Van Soest ADF-ADL) on the faecal digestibility and rate of passage in growing rabbits (31-53 days of age) was studied using five diets ( table I): a control diet (RO) with a low cellulose content (9.3%) and four diets with increasing cellulose content (12.4 and 15.9%) (table I II) provided either by wheat straw and alfalfa (diets P1 and P2) or by soya bean hulls and alfalfa (diets CS1 and CS2). Cellulose was replac ed mainly by starch without change in the dietary lignin and hemicellu lose levels. Organic matter digestibility (%) increased linearly as th e level of cellulose decreased (+1.7 point per point of cellulose). Cr ude protein digestibility was similar between P2 and RO (mean 78%) but increased by 12 points (P < 0.01) between CS2 and RO. Reducing the le vel of cellulose (-40%) decreased by 50% the intake of cellulose and l ed to a higher neutral detergent fibre (NDF) digestibility (+25%). How ever, the quantity of NDF digested daily (mean 9 g/day) was unchanged either by the level or by the origin of the cellulose. As the intake o f cellulose was reduced, the whole tract mean retention time increased (mean, +3 h), but more for the diets P (13.4 to 18.5 for diets P2 and RO, respectively) than for the diets CS (15.4 h for CS2). In the caec ocolic compartments the rate of passage of the fine particles was unaf fected while the transit of raw particles tended to be shorter (P = 0. 10) for the diet CS2. The minimum transit time (TTm) was longer (+2 h) according to the reduction of the level of cellulose without a signif icant effect of the cellulose origin.