The role of starch and fiber composition on nutrient flow, site and extent of nutrient digestion, and microbial profiles in pigs

Abstract

Starch is the main energy substrate for monogastrics, including swine. Physico- chemical properties of starch and the cereal grain matrix can change the kinetics of digestion. Objectives of this thesis were to enhance the understanding of how the physico-chemical properties of purified starch and starch and fiber from whole grains can alter the site and extent of nutrient digestion, microbial and metabolite profiles, and efficiency of energy utilization. In study 1, weaned pigs (n = 32) were fed one of four diets containing 67% starch with 0, 20, 28, or 63% amylose for 21 d. Increasing dietary amylose linearly increased post-ileal flow of dry matter and starch, hindgut fermentation, and cecal and colonic digesta Bifidobacterium spp. However, increasing levels of dietary amylose linearly reduced feed intake and growth indicating high amylose may be less energy efficient than rapidly digestible starch. In studies 2 and 3, 5 whole grains: (% amylose, β-glucan, total dietary fiber (TDF)): 1) high-fermentable, high β-glucan hull-less barley (HFB) (0, 10, 22); 2) high-fermentable, high amylose hull-less barley (HFA) (18, 7, 18); 3) moderate-fermentable hull-less barley (MFB) (11, 5, 15); 4) low fermentable hulled barley (LFB) (11, 4, 17); and 5) low fermentable hard red spring wheat (LFW) (12, 1, 14) were fed to ileal cannulated pigs (n = 7) in a 6 (periods) × 7 (diets) Youden square design. Fermentability of grains was based on the β-glucan content. Highly fermentable whole grains, HFB and HFA, had decreased ileal digestibility of dry matter, starch, and amino acids. However HFB and HFA had increased hindgut substrate availability and starch and DM fermentation. Increased ileal flow of starch from HFB and HFA was positively correlated to a shift in fecal microbial profile towards Firmicutes, including ii genera Dialister and Sharpea. In study 4, weaned pigs (n = 6/treatment) were fed one of six diets in a 3 (wheat (W) (%amylose, %β-glucan, %TDF) (12, 1, 14), digestible hull- less barley (dHB) (11, 5, 15), and fermentable hull-less barley (fHB) (18, 7, 18) × 2 (SBM or autoclaved soybean meal (aSBM)) factorial arrangement for 18 days. Higher viscosity of dHB and fHB increased post-ileal β-glucan flow, providing a fermentative substrate to the hindgut. Increased hindgut substrate availability from hull-less barley shifted the colonic microbiota towards Firmicutes and Actinobacteria and increased total tract nutrient digestibility and piglet feed efficiency. The findings from this thesis provide evidence that physico-chemical properties of starch and fiber are important determinants of digestion kinetics. Dietary inclusion of high amylose starch or fermentable fiber has shown to increase hindgut substrate availability and shift microbial and metabolite profiles. Thus amylose or cereal grains high in fermentable fiber may be beneficial for dietary inclusion if careful consideration of efficiency of energy utilization and amino acid digestibility is taken to ensure adequate pig growth performance.