There is growing interest in vegan and vegetarian (veg*n) diets for dogs and cats, due to factors including pet health, environmental sustainability and farmed animal welfare. Such diets should be carefully designed and manufactured in order to be nutritionally sound. Digestibility is a key, although not the only, determinant of this, and it has sometimes been claimed that dogs and cats cannot effectively digest and utilize plant-based proteins. To evaluate this claim, studies assessing canine and/or feline digestibility of veg*n diets and ingredients were analyzed. Thirty-one studies were included: 22 specific to dogs, two specific to cats, and seven applicable to both species. Across various study designs, populations, digestibility metrics, dietary ingredients and processing methods, digestibility values of veg*n diets were consistently high and broadly comparable to those of conventional meat-based diets. In all five studies that assessed apparent total tract digestibility (ATTD) of veg*n pet diets, ATTD values exceeded 80% (dry matter), 85% (organic matter), 80% (crude protein), 89% (fat), 88% (nitrogen-free extract), and 86% (energy). These studies also indicate that individual vegan protein sources can be well digested by dogs and/or cats, including those derived from legumes (such as soy-derived ingredients), pulses, grains and microbial fermentation. Discrepancies exist regarding whether these ingredients are more, less or equally digestible compared to animal-based alternatives. Nevertheless, even in studies where vegan protein sources showed lower digestibility for specific nutrients, overall digestibility remained high. These findings support the use of nutritionally sound veg*n pet diets. Such diets are not normally significantly less digestible than conventional meat-based diets.
Andrew Knight (Sat,) studied this question.