EFFECT OF DIETARY STARCH ORIGIN ON DIGESTION IN THE RABBIT .2. STARCHHYDROLYSIS IN THE SMALL-INTESTINE, CELL-WALL DEGRADATION AND RATE OF PASSAGE MEASUREMENTS

Starch hydrolysis in the small intestine could vary according to the t ype of starch, thus affecting the quantity of starch entering the caec um and the fermentation activity. Variations in the concentration of u ndegraded starch at the ileum, fibre digestibility and rate of passage were investigated for four diets, differing mainly in the source of s tarch: purified maize starch (PMS), maize, barley or pea. The diets we re similar in starch and neutral-detergent fibre (NDF) content (means of 280 and 279 g kg-1 DM, respectively) and in crude protein content ( mean 224 g kg-1 DM). They were given (100 g day-1) to four adult rabbi ts (3.2-3.6 kg live weight) cannulated at the terminal ileum. Ileal di gesta were sampled 2, 3 and 4 h after a test meal, to estimate residua l starch after enzymic hydrolysis in the small intestine. Nutrient dig estibility was measured from total faecal collection for 6 consecutive days, and rate of passage was measured at the ileal level and in the whole tract, using cerium-141-labelled cell wall particles. Whole-trac t digestibility of starch was almost complete whatever the diet, only a slight reduction being observed for maize. The ileal starch concentr ation differed markedly according to starch origin, from 0.6% for the barley diet to almost 3% for the maize diet. Starch from pea was almos t completely degraded in spite of a high dietary inclusion level (60%) . For a similar fibre content in the four diets, the quantity of diges ted NDF was positively correlated to the ileal flow of starch (r=0.89) . Mean retention time in the whole tract (mean 21 h) and between ileum and rectum (mean 16.5 h) increased (+ 10%) when the ileal starch leve l became higher (pea and maize diets). This suggest a possible control of rabbit caecal fermentation and rate of passage by modifying the hy drolysis in the intestine according to the type of dietary starch.