The effect of digestive bypass macronutrients and age on stool quality (moisture and firmness) in dogs and cats is not well understood. Data were analyzed from digestibility tests (n = 2020, 361 dogs and 536 cats) including dry and wet product types. Both food and feces were measured for moisture and nutrients according to standard protocols; stool firmness was graded. Linear mixed modeling was used to evaluate the associations between nutrient bypass, age and stool quality. Bypass protein increased stool moisture (dog, cat p < 0.0001) and decreased firmness (dog p = 0.01, cat p < 0.0001), while bypass fiber decreased stool moisture and increased firmness (dog, cat p < 0.0001 for both). Both species manifested a negative quadratic effect of advanced age on stool firmness (dog p < 0.0001 and cat p = 0.02). However, the association of advanced age (quadratic effect) with metabolizable energy required to maintain body weight was different between species; dogs had a positive association (p = 0.028), while it was negative for cats (p < 0.0001). Taken together, these data may aid in the development of food formulations for companion animals, which can better meet changing nutritional needs across life stages.
Keywords: age; cat; digestibility; dog; fecal quality; macronutrients; stool.