Comparative digestion and fermentation characteristics of low-tannin or high-tannin sorghum grain in the porcine gastrointestinal tract

High-tannin sorghum grain (HTS) has been previously proved to contain lower apparent total tract digestibility (ATTD) of nutrients than low-tannin sorghum grain (LTS) for pigs. This study was conducted to identify in which segments (foregut or hindgut) of the intestinal tract of pigs the digestion of nutrients was mostly influenced, and to compare the digestion and fermentation characteristics of LTS and HTS in the porcine gastrointestinal tract. In experiment 1, HTS and LTS were digested by porcine pepsin and pancreatin to simulate small intestine digestion, and subsequently the undigested residues were incubated with fresh pig cecal digesta as inoculums for 48 h to simulate the porcine large intestine fermentation in vitro. The results revealed that the in vitro digestibility of air-dry matter, gross energy (GE), and crude protein (CP) was lower (P < 0.05) in HTS than that in LTS, regardless of the simulated small intestine digestion or large intestine fermentation. The enzymatically unhydrolyzed residue of HTS decreased the accumulative gas production excluding the first 3 h and the short-chain fatty acid concentration including acetic acid, propionic acid, and butyric acid in the fermented solutions (P < 0.05), although it provided more nutrients as fermentation substrates (P < 0.05). In experiment 2, 12 crossbred barrows (25.5 ± 2.5 kg body weight) with a T-cannula inserted in the distal ileum were randomly allotted to two diets (N = 6) to determine nutrient digestibility in the foregut (AID, apparent ileal digestibility) and in the hindgut of pigs (HGD, hindgut disappearance). The study lasted 10 d, with a 5 d adaption to the diets followed by a 3 d collection of feces and then a 2 d collection of ileal digesta. Diets included 96.6% HTS or LTS as the only source of dietary energy and nitrogen. The AID and ATTD of dry matter, GE, and CP in HTS were lower than those in LTS (P < 0.05). There was no difference in HGD of nutrients between LTS and HTS. Eight out of fifteen amino acids in HTS had lower AID values (P < 0.05). In conclusion, HTS provided lower small intestine digestibility of nutrients and lower large intestine fermentation parameters, implying that condensed tannins in sorghum grain may impede the nutrient digestibility in the foregut and limit the fermentability in the hindgut segment of pigs. Hence, digestion and fermentation characteristics of sorghum grain may vary depending on the condensed tannins.