Extruded feline diets formulated with high inclusion of soybean hulls: effects on apparent total tract macronutrient digestibility, and fecal quality and metabolites.

Dietary fibers have gained renewed interest in companion animal nutrition as a means to manage pet obesity and improve gut and host health. Soybean hulls (SBH), a coproduct of the soybean oil extraction process, is an accessible and economical fiber source. However, limited research is available on the use of SBH in feline nutrition. Thus, the aim of this study was to determine the effects of a high SBH inclusion level on daily food intake, apparent total tract (ATT) macronutrient digestibility, fecal quality, and fecal fermentative end products in diets of adult cats. Four diets were formulated with either SBH, beet pulp (BP), or cellulose (CL) as the main source of dietary fiber, with the control diet formulated with no added fiber (NF). The fiber treatments were formulated to achieve approximately 15% total dietary fiber (TDF). Eight adult male cats (mean age = 10.5 yr ± 0.1; mean BW = 6.1 ± 0.8 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. Food was offered twice daily and cats were fed to maintain BW. Food intake on a DM basis (DMB) was lower (P < 0.05) in cats fed BP (55.2 g/d) when compared with SBH (70.8 g/d). As-is fecal output did not differ in cats fed BP or SBH, and when expressed on a DMB, fecal output did not differ among fiber treatments. The ATT digestibility of DM, OM, and GE was greater (P < 0.05) in cats fed NF when compared with those fed BP, CL, or SBH. Cats fed CL had the greatest (P < 0.05) ATT CP digestibility (88.5%), followed by cats fed NF (84.9) and SBH (81.7%) with the lowest values (77%) noted for cats fed BP. Acid-hydrolyzed fat (AHF) digestibility was greater for cats fed CL (92.9%) than for cats fed BP (86.9%) and SBH (88.6%). The TDF ATT digestibility was lowest for cats fed NF and CL (8.5% and 15.1%, respectively), followed by SBH (18.0%), with BP having the highest digestibility (33.7%). Total short-chain fatty acid concentration was greatest (P < 0.05) in cats fed BP (699.7 μmole/g) when compared with the other 3 treatments, whereas phenol and indole concentrations did not differ among treatments. In conclusion, a high inclusion level (15% TDF) of SBH appears acceptable in diets for adult cats, resulting in no negative effects on daily food intake, fecal scores, and similar ATT digestibility for most macronutrients when compared with BP and CL.