Effects of high inclusion of soybean hulls on apparent total tract macronutrient digestibility, fecal quality, and fecal fermentative end-product concentrations in extruded diets of adult dogs.

Soybean hulls (SBH) are a fiber-rich co-product of the soybean oil extraction process that corresponds to 8% of the soybean seed. Despite being readily available and priced competitively, SBH are underutilized in monogastric nutrition. Thus, the objective of this study was to evaluate SBH as a dietary fiber in canine diets. Four diets were formulated with either SBH, beet pulp (BP), or cellulose (CL) as the main source of dietary fiber (15% total dietary fiber [TDF]), with the control diet formulated with no supplemental fiber (NF). Animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee. Eight adult female Beagle (mean age = 4.6 ± 0.6 yr; mean BW = 12.8 ± 1.7 kg) were used in a replicated 4 × 4 Latin square design. Each period consisted of 14 d, with 10 d of diet adaptation followed by 4 d of total fecal and urine collections. At the end of each period, a blood sample was collected and analyzed for serum chemistry. Food was offered twice daily and fed to maintain body weight. Food intake (g/d) on a dry matter basis (DMB) did not differ among treatments. Fecal score was lower (P < 0.05) for dogs fed CL (2.0) in contrast with other dietary treatments (2.3), using a 5-point scale (1 = hard, dry pellets; 5 = diarrhea). Fecal as-is and DM output did not differ for dogs fed BP, CL, or SBH, and were approximately 50% greater (P < 0.05) than dogs fed NF. Apparent total tract digestibility (ATTD) of dry matter, organic matter, and gross energy were greater (P < 0.05) for dogs fed NF when compared with dogs fed BP, CL, or SBH. Dogs fed CL had greater (P < 0.05) AHF ATTD (94%) compared with all other treatments (mean = 91%). Dogs fed CL and NF had greater (P < 0.05) CP ATTD, 87% and 86%, respectively, while dogs fed SBH were intermediate (83%) and dogs fed BP were lowest (79%). Total short-chain fatty acid (SCFA) concentration was greatest in dogs fed BP (582.5 μmol/g) and SBH (479.7 μmol/g) when compared with NF and CL (267.0 and 251.1 μmol/g, respectively). Serum metabolites were within-reference ranges and dogs remained healthy throughout the study. In conclusion, SBH resulted in similar macronutrient ATTD when compared with BP and CL. Dogs fed SBH were also observed to have an increase in fecal SCFA concentration. In general, high level addition of SBH were well-utilized by the dog, resulting in no untoward effects on dog health, nutrient digestibility, or fecal characteristics.