The contribution of digestible and metabolizable energy from high-fiber dietary ingredients is not affected by inclusion rate in mixed diets fed to growing pigs.

Effects of inclusion rate of fiber-rich ingredients on apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of GE and on the concentration of DE and ME in mixed diets fed to growing pigs were determined. The hypothesis was that increasing the inclusion rate of fiber decreases digestibility of GE, and thus, the contribution of DE and ME from hindgut fermentation because greater concentrations may reduce the ability of microbes to ferment fiber. Twenty ileal-cannulated pigs (BW: 30.64 ± 2.09 kg) were allotted to a replicated 10 × 4 incomplete Latin Square design with 10 diets and four 26-d periods. There were 2 pigs per diet in each period for a total of 8 replications per diet. A basal diet based on corn and soybean meal (SBM) and a corn-SBM diet with 30% corn starch were formulated. Six additional diets were formulated by replacing 15% or 30% corn starch by 15% or 30% corn germ meal, sugar beet pulp, or wheat middlings, and 2 diets were formulated by including 15% or 30% canola meal in a diet containing corn, SBM, and 30% corn starch. Effects of adding 15% or 30% of each fiber source to experimental diets were analyzed using orthogonal contrasts and t-tests were used to compare inclusion rates within each ingredient. The AID and ATTD of GE and concentration of DE and ME in diets decreased (P < 0.05) with the addition of 15% or 30% canola meal, corn germ meal, sugar beet pulp, or wheat middlings compared with the corn starch diet. However, inclusion rate did not affect the calculated DE and ME or AID and ATTD of GE in any of the ingredients indicating that concentration of DE and ME in ingredients was independent of inclusion rate and utilization of energy from test ingredients was equally efficient between diets with 15% and 30% inclusion. Increased inclusion of fiber in the diet did not influence transit time in the small intestine, but reduced the time of first appearance of digesta in the feces indicating that transit time was reduced in the hindgut of pigs fed high-fiber diets. However, this had no impact on DE and ME or ATTD of GE in test ingredients. In conclusion, fiber reduced the DE and ME in the diet. However, inclusion rate of fiber-rich ingredients in diets did not affect calculated values for DE and ME in feed ingredients indicating that microbial capacity for fermentation of fiber in pigs is not overwhelmed by inclusion of 30% high-fiber ingredients in the diets.