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High amylose starch increases post‐ileal nutrient flow, microbial fermentation, and bifidobacteria in pigs

Starch chemistry affects enzymatic digestion of starch and thereby starch availability for microbial fermentation. The effect of starch chemistry on post‐ileal nutrient flow and microbial activity was studied in 8 ileal‐cannulated pigs (29.4 kg BW) each fed 4 diets containing 70% purified starch (amylose content, < 5, 20, 28 and 63%; reflected by in vitro maximal digestion rate; 1.06, 0.73, 0.38, and 0.22%/min, respectively). Amylose content and in vitro digestion rate of starch quadratically affected (P < 0.001) post‐ileal starch flow (4.1, 3.7, 4.1 and 405 mg/g starch fed; respectively, for low to high amylose and rapid to slow digestion rate), fecal total SCFA (10.5, 9.6, 16.2 and 28.7 μmol/g of DM fed) and butyrate concentration (1.1, 1.0, 2.5, and 2.9 μmol/g of DM fed), and fecal bifidobacteria (5.6, 5.2, 5.1, and 6.6 log rDNA gene copies/g). Gene copy numbers of the Lactobacillus group, Enterococcus, Streptpcoccus, Enterobacteriaceae, Bacteroides‐Prevotella‐Porphyrmona and Clostridial clusters I, IV and XIV in ileal digesta and feces did not differ (P < 0.05) among starches. In conclusion, starch with high amylose and low in vitro digestibility increased post‐ileal nutrient flow and microbial fermentation, and selectively promoted growth of bifidobacteria in the distal gut. Substantial changes of starch chemistry (≥45% amylose and ≤0.34%/min in vitro digestion rate) were required to alter the post‐ileal variables in pigs.