Cecum is the major degradation site of ingested inulin in young pigs

Two groups have reported >90% of inulin digestion occurs before the cecum in pigs and argued against pigs as a proper animal model for humans in this regard. Two experiments were conducted with weanling pigs to characterize the hydrolysis profile of inulin in their digestive tracts. In Expt. 1, 12 pigs (weighing 7.7 +/- 0.2 kg) were fed a low-iron (54 mg/kg) corn-soy basal diet (BD) or BD + 4% inulin (Synergy 1, Orafti) for 6 wk. All pigs were killed at the end of the trial and digesta samples were collected from the stomach, upper and lower jejunum, cecum, and proximal, mid-, and distal colon. Inulin was detected in digesta from the first 3 segments (0.4-5.5% dry matter) but not from the large intestine of pigs fed inulin. Fructose concentrations in digesta from the stomach and jejunum were greater (P < 0.05) in pigs fed inulin than in those fed BD. To further determine whether inulin was degraded in the ileum or cecum, we conducted Expt. 2 with 12 pigs (weighing 11.2 +/- 1.1 kg) for 8 wk as in Expt.1 except that digesta samples were collected from the ileum instead of upper jejunum. Likewise, inulin was detected only in digesta from stomach, jejunum, and ileum of pigs fed inulin. Although inulin-degrading activity was detectable in digesta from the ileum, cecum, and proximal colon of both groups, the highest activity (P < 0.05) was found in the cecum digesta of pigs fed inulin. Digesta from the cecum and colon, but not from the ileum, was able to degrade added inulin in in vitro incubations. We conclude that supplemental dietary inulin in young pigs was mainly degraded in their cecum.