Animal proteins are commonly used in extruded dog foods. Plant-based proteins have a more consistent nutrient profile than animal sources but may contain antinutritional factors, including trypsin inhibitors and oligosaccharides. Bioprocessed soy protein (SP; HP-300; Hamlet Protein, Inc., Findlay, OH) is a processed soy-based product with low antinutritional factor concentrations and high protein quality. The objective of this study was to evaluate the effects of SP on apparent total tract macronutrient digestibility, fecal characteristics, and fecal fermentative end products. The study was also to determine whether SP could be a replacement for poultry byproduct meal (PBPM) in dog food.

Forty-eight Beagle dogs were randomly assigned to one of six treatments (0 (control), 4, 8, 12, 24, and 48% SP) and fed a 30% crude protein and 16% fat diet.  Palatability studies compared 0, 12, or 48% SP diets.  The palatability results suggest that of the 3 inclusion levels tested (0, 12, or 48% SP), the best inclusion of SP is 12%, which was preferred over 0 and 48% SP.   Digestibility of dry matter, organic matter, and energy did not differ from the control at any inclusion rate, except for a decrease (P < 0.01) at 48% SP.  Apparent total tract crude protein digestibility was not affected by treatment and ranged from 82.9 to 86.2%.   Stool output (on both an as-is and a DM basis) did not differ from the control except for the 48% SP treatment (P < 0.01).  Treatment had no effect on stool consistency scores.  The researchers concluded that SP is a suitable replacement for PBPM in dog diets up to a 24% inclusion level.