The digestibility of vegan and vegetarian diets for dogs and cats

Jade Alanya Warren^1*Billy Nicholles^1,2Andrew Knight^1,3,4,5Antonia Chan¹

• ¹Sustainable Pet Food Foundation, London, United Kingdom
• ²Bryant Research Ltd, London, United Kingdom
• ³University of Winchester Faculty of Health and Wellbeing, Winchester, United Kingdom
• ⁴Murdoch University School of Veterinary Medicine, Murdoch, Australia
• ⁵Griffith University School of Environment and Science, Nathan, Australia

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. While transitioning companion animals to veg*n diets could offer significant ethical and environmental benefits, it has been claimed that dogs and cats can more easily absorb and utilize animal-based protein than plant-based protein. This review collates and analyzes studies on the digestibility of veg*n diets for dogs and cats. Thirty-one studies were included: 22 were specific to dogs, two were specific to cats, and seven were applicable to both species. The collective scientific evidence demonstrates that veg*n diets are normally and effectively digested by dogs and cats when formulated to be nutritionally sound. Across various study designs, populations, digestibility metrics, dietary ingredients and processing methods, digestibility values were consistently high and broadly comparable to those of conventional meat-based diets. In all five studies identified 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). Current evidence also indicates that individual vegan protein sources are well digested by dogs and cats, including legumes (such as soy-derived ingredients), pulses, grains and microbial proteins. 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 veg*n pet diets, challenging the notion that such diets are inherently less digestible than conventional meat-based diets.