Hydrolysis site and action mode of supplemental dietary inulin in gastrointestinal tract of weanling pigs

We have previously shown a positive effect of supplemental inulin on bioavailability of intrinsic Fe in a corn‐soybean meal basal diet (BD) for weanling pigs. Two experiments were conducted to determine mechanisms for that benefit of inulin. In Exp. 1, 12 pigs (7.7 ± 0.2 kg BW) were fed the low‐iron (54 mg/kg) BD or BD + 4% inulin (Synergy 1, Orafti, Tienen, Belgium) for 6 wk. All pigs were killed at the end of the trial to collect digesta samples from stomach, upper and lower jejunum, cecum, and proximal, mid, and distal colon. Strikingly, inulin was detected only in digesta from the first three segments (0.4 to 5.5%, dry basis), but not from the large intestine of pigs fed inulin. Fructose concentrations in digesta from stomach and both parts of jejunum were greater (P < 0.05) in pigs fed inulin than those fed BD. To further determine if and how inulin was degraded mainly in ileum or cecum, we conducted Exp. 2 with 12 pigs (11.2 ± 1.1 kg BW) for 8 wk as did in Exp.1. except for that ileum instead of upper jejunum digesta samples were collected. Likewise, inulin was detected only in digesta from stomach, jejunum, and ileum of pigs fed inulin. Although inulianse activity was detectable in digesta from ileum, cecum, and proximal colon of both groups, the highest activity (P < 0.05) was found in the cecum digesta of pigs fed inulin. In conclusion, supplemental dietary inulin was degraded mainly in cecum where inulinase activity was induced by the supplementation. The elevated fructose concentration in the upper gut of pigs fed inulin might be beneficial for iron absorption.