38 Increasing dietary amylose increases hindgut fermentation of starch and thereby alters microbial metabolites, gut immunity, and energy metabolism in weaned pigs.

Abstract Starch with increasing ratio of amylose to amylopectin decreases ileal starch digestibility in pigs. Microbes in the large intestine ferment undigested starch producing short-chain fatty acids (SCFA). Benefits of SCFA for gut health stimulated interest in dietary strategies to increase carbohydrate fermentation and thus SCFA concentration in the gut. This study elucidated effects of increasing dietary amylose on nutrient digestibility, metabolite profiles, gut immunity, and lipid metabolism in weaned pigs. Weaned pigs (n = 32) were randomly fed 1 of 4 diets containing 67% purified starch varying in amylose content (0, 20, 35, or 70%) for 21 d. Pigs were euthanized to collect digesta, feces, blood, and tissue samples for measuring starch digestion, metabolite profiles, and genes associated to metabolite transport, butyrate production, gut immunity, and lipid metabolism. Increasing dietary amylose quadratically decreased ileal digestibility of starch (P < 0.001) and quadratically increased hindgut fermentation of starch (P < 0.001) and cecal (P < 0.001) and colonic (P < 0.05) digesta SCFA concentration. Increasing dietary amylose upregulated expression of SCFA transporters in the mid colon (P < 0.05) but downregulated GPR109A in the proximal colon (P < 0.05). The 35%-amylose diet upregulated mucosal expressions of tight junction proteins in ileum and proximal colon (P < 0.05). Increasing dietary amylose quadratically downregulated expression of fatty acid synthase in abdominal fat and liver (P < 0.05) and quadratically increased butyrate production pathway genes (P < 0.05). Total SCFA concentration was negatively correlated with pro-inflammatory cytokines (P < 0.05). Butyrate concentration was positively correlated with mucin-2 (P < 0.05). In conclusion, increasing dietary amylose enhanced hindgut starch fermentation and total SCFA levels in weaned pigs. The increased carbohydrate fermentation was associated with increased butyrate production enzymes and improved gut health mechanisms including maintenance of gut barrier function and reduced proinflammatory cytokine. High-amylose starch reduced lipogenesis by downregulating lipogenic enzyme gene expression.