Is it possible for dogs to have a vegetarian diet?

Question

I have seen some people claim that dogs can be kept healthy on a vegetarian diet, while other people emphatically deny this and yet more say "No! Unless you're really careful".

Can dogs be kept healthy — not just alive, but healthy — on a vegetarian (or vegan, or pescatarian) diet?

I've been curious about this for some time, but the answers I've seen have been contradictory, often based on the author's own diet as a human, and in many cases either unsourced or from clearly biased groups like PETA and The Vegetarian Society.

One consistent part of both "yes" and "no" answers is the need for taurine in their diet, but apparently this is available in synthetic form. I am therefore also curious about the effectiveness of synthetic dietary supplements for whatever would be missing from an "natural" vegetarian/vegan/pescatarian diet.

I'm especially interested in references to scientific papers on this topic, if they are available.

Answer 1

In brief summary, "Yes, but."

To answer my own question, there is some real research on vegetarian diets for canines:

Nutritional and ethical issues regarding vegetarianism in the domestic dog

(Citation: W.Y. Brown, Recent Advances in Animal Nutrition – Australia 17 (2009))

Summary

Many dog owners wish to feed their dogs a vegetarian diet for the same ethical reason that they themselves are vegetarian. To meet this demand, there are an increasing number of vegetarian diets and recipes available for dogs. However, proof for their claims of nutritional adequacy is often lacking. There is little doubt that a dog’s nutritional requirements can be met from a diet that does not contain meat; however, the difference between the amino acid profiles of plant and animal proteins must be considered. It has been shown that exercising dogs may develop anaemia when fed unbalanced plantprotein diets but will remain in good health if the meatfree diet is correctly balanced. Many plant ingredients contain high levels of non-starch polysaccharides and other anti-nutritive factors, which may reduce the availability of some nutrients. A diet devoid of animal ingredients is also likely to be of low palatability to dogs. All diets should be correctly formulated to meet nutrient requirements based on chemical analysis and predicted or measured apparent digestibility, should be sufficiently palatable to ensure adequate dietary intake and should maintain good health when consumed. If a vegetarian diet meets all of these criteria, then it is a suitable diet for the dog, irrespective of the owner’s motivation for feeding a vegetarian diet.

Conclusions

The nutritional adequacy of a diet, vegetarian or otherwise, should be based on the ability of the diet to meet nutritional requirements. Palatability and digestibility are key considerations. A large number of dogs are currently fed meat-free diets, and there is a small but growing niche market for vegetarian pet foods. The major pet food manufacturers are unlikely to enter this market until there is greater acceptance of this type of product. Should this eventuate, it is hoped that their participation will ensure that the nutritional adequacy of commercial vegetarian dog foods is validated by recognised feeding protocols and digestibility trials.