Whole-Grain Fiber Composition Influences Site of Nutrient Digestion, Standardized Ileal Digestibility of Amino Acids, and Whole-Body Energy Utilization in Grower Pigs

Background: Variant chemical composition and physical structure of whole grains may change the site of energy digestion from the small to the large intestine. Objective: We determined the site of nutrient digestion, standardized ileal digestibility (SID) of amino acids (AAs), and net energy (NE) value of barley cultivars that vary in nutrient composition compared with wheat. Methods: Ileal-cannulated barrows (27.7 kg initial body weight) were fed diets containing 800 g whole grains/kg alongside a basal and nitrogen-free diet for calculations in a 6 (period) x 7 (diet) Youden square. Diets included 1 of 5 whole grains-1) high-fermentable, high-beta-glucan, hull-less barley (HFB); 2) high-fermentable, high-amylose, hull-less barley (HFA); 3) moderate-fermentable, hull-less barley (MFB); 4) low-fermentable, hulled barley (LFB); and a low-fermentable, hard red spring wheat (LFW). Intestine nutrient flow and whole-body energy utilization were tested and explained by using whole-grain and digesta confocal laser scanning. Results: Starch apparent ileal digestibility was 14-29% lower (P <0.05) in HFB and HFA than in MFB, LFB, and LFW due to the unique embedding of starch within the protein-fiber matrix of HFB and the high amylose content in HFA. Starch hindgut fermentation was 50-130% higher (P < 0.05) in HFB and HFA than in MFB, LFB, and LFW. The SID of indispensable AAs was lower (P< 0.05) in HFB and HFA than in MFB, LFB, and LFW. NE value was 18% higher (P< 0.05) for HFB than for HFA and was not different from MFB, LFB, and LFW. Conclusions: Whole grains high in fermentable carbohydrates shifted digestion from the small intestine to the hindgut. NE value depended on the concentration of fermentable fiber and starch and digestible protein, ranging from 2.12-1.76 Mcal/kg in barley to 1.94 Mcal/kg in wheat. High-fiber whole grains may be used as energy substrates for pigs; however, the reduced SID of AAs requires titration of indispensable AAs to maintain growth.