Digestibility and palatability of extruded dog food with <i>Aspergillus oryzae</i> fermented soybean meal and its influence on colonic fermentation Indicators

This study aimed to compare Aspergillus oryzae fermented soybean meal with traditional soybean products in extruded diets on digestibility, colonic fermentation and palatability when fed to dogs. Four diets using differed soybean products (30% soybean meal, SBM; 30% soybean meal + 1% dry A. oryzae biomass product, AMF; 30% fermented soybean meal, FSBM; and 18% soybean protein isolate, SPI) were fed to 12 adult dogs in a replicated 4 × 4 Latin square design. Dogs were adapted to diets for 9 days followed by a 5-day total fecal collection and fresh fecal collection. Apparent total tract digestibility (ATTD) was calculated by total fecal collection method and indirect marker (titanium dioxide) method. Data were analyzed with a generalized linear mixed model (GLIMMIX; SAS version 9.4) with diet as fixed effect and dog and period as random effects. Dogs fed with SPI had lower (P<0.001) fecal output and defecation frequency than dogs fed with other diets. Dogs fed with FSBM had ATTD of organic matter, crude protein and gross energy similar to dogs fed with SBM, but lower (P<0.05) than those fed with SPI regardless of estimation method. The ATTD of dry matter, as calculated by the marker method, was greater (P<0.001) in dogs fed with FSBM diet compared to those fed with SBM. Fecal pH was greater (P<0.05) in dogs fed with SPI than in those fed with SBM and AMF, with dogs fed with FSBM intermediate. While fecal ammonia content was similar across dogs, short-chain fatty acid (SCFA) content was the lowest (P<0.05) in dogs fed with SPI and the highest (P<0.05) in those fed with AMF. Acetate, propionate, and total volatile fatty acid (the sum of SCFA and BCFA) contents mirrored the ranking of SCFA. Percentage of propionate and SCFA to total volatile fatty acids were lower (P<0.05), whereas those for butyrate, isovalerate, and branched-chain fatty acids (BCFA) were higher (P<0.05) in dogs fed with SPI diet compared to dogs on other diets. Palatability trials were conducted with 20 dogs over 2 days. Data were analyzed with a 1-way ANOVA, a paired t-test and a Chi2 test at significance level of α = 0.05. Dogs showed preference (P<0.05) for SBM over FSBM, but differences between SBM, AMF, and SPI were insignificant. In conclusion, the A. oryzae fermented soybean meal-based diet was less palatable than regular soybean meal-based diet but they induced similar stool quality, nutrient digestibility and colonic fermentation pattern in dogs.