Disappearance of nutrients and energy in the stomach and small intestine, cecum, and colon of pigs fed corn-soybean meal diets containing distillers dried grains with solubles, wheat middlings, or soybean hulls.

Disappearance of nutrients and energy in the stomach and small intestine, cecum, and colon of pigs fed diets containing distillers dried grains with solubles (DDGS), wheat middlings, or soybean hulls was determined. A second objective was to test the hypothesis that physical characteristics of dietary fiber in diets are correlated with the digestibility of nutrients and energy. Eight barrows (initial BW = 37.3 ± 1.0 kg) with a T-cannula in the distal ileum and another T-cannula in the proximal colon were allotted to a replicated 4 × 4 Latin square design with 4 diets and 4 periods in each square. The basal diet was a corn-soybean meal diet and 3 additional diets were formulated by substituting 30% of the basal diet with DDGS, wheat middlings, or soybean hulls. Following an 8-d adaptation period, fecal samples were collected on d 9 and 10, and samples from the colon and the ileum were collected on d 11 and 12, and d 13 and 14, respectively. Values for apparent ileal digestibility (AID), apparent cecal digestibility (ACD), and apparent total tract digestibility (ATTD) of nutrients and energy were calculated. Results indicated that ACD and ATTD of soluble dietary fiber was not different regardless of diet indicating that the soluble dietary fiber is mostly fermented in the small intestine or in the cecum. Pigs fed the wheat middlings diet had greater ( ≤ 0.05) ACD of insoluble dietary fiber compared with pigs fed diets containing DDGS or soybean hulls indicating that the insoluble fiber in wheat middlings may be more fermentable than insoluble fiber in DDGS or soybean hulls. Insoluble dietary fiber disappearance in the colon of pigs fed the soybean hulls diet was greater ( ≤ 0.05) compared with the DGGS containing diet indicating that insoluble fiber in DDGS are more resistant to fermentation than insoluble fiber in soybean hulls. The ATTD of total dietary fiber in wheat middlings was greater ( ≤ 0.05) than in DDGS and soybean hulls further indicating that fiber in wheat middlings are more fermentable than fiber in DDGS and soybean hulls. Water binding capacity, bulk density, and viscosity of dietary fiber were not correlated with digestibility of nutrients and energy regardless of the diet. In conclusion, soluble dietary fiber is mostly fermented before reaching the colon whereas insoluble dietary fiber is mostly fermented in the colon, but fiber in wheat middlings is more fermentable than fiber in DDGS or soybean hulls.