Soybean Hulls As a Sustainable Dietary Fiber Source in Canine Diets

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 the use of 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), with the last diet formulated with no supplemental fiber (NF). All animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee. Eight adult female beagles (mean age = 4.6 ± 0.6 r; mean BW = 12.8 kg ± 1.7 kg) were used in a replicated 4x4 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. The data were analyzed using mixed model procedure of SAS and a P < 0.05 was considered statistically significant. Food intake (g/d) on a dry matter basis (DMB) did not differ among treatments. Fecal score was lower (P < 0.05) in dogs fed CL in contrast with other dietary treatments, 2.0 vs. 2.3, respectively, using a 5-point scale. As-is and DM fecal output did not differ in dogs fed BP, CL, or SBH and were approximately 50% lower (P < 0.05) in dogs fed NF. Apparent total tract (ATT) dry matter, organic matter, and gross energy digestibilities were greater (P < 0.05) in dogs fed NF when compared to dogs fed BP, CL, or SBH. Dogs fed CL had greater (P < 0.05) ATT fat digestibility (94%) among all treatments (avg. 91%). Dogs fed CL and NF had greater (P < 0.05) ATT crude protein digestibility, 87% and 86%, respectively, while dogs fed SBH was intermediate (83%) and dogs fed BP was lowest (79%). Serum metabolites were within reference ranges and animals remained healthy throughout the study. In conclusion, SBH resulted in similar ATT macronutrient digestibility when compared to BP and CL; fiber sources widely used in commercial pet foods. In general, moderate inclusion of dietary fiber sources decreased ATT macronutrient digestibility in dogs in contrast to NF.