There is a great deal of confusion (and opinion) today regarding how to classify the domestic dog. Those who identify dogs as carnivores (meat-eating) animals tend to focus on the predatory nature of the dog’s closest cousin, the wolf. Conversely, those who are inclined to classify the dog as an omnivore (consumes both plants and meat) rely upon the dog’s scavenging nature and ability to consume and digest a wide variety of food types. So, which is it? And, perhaps more importantly why does what we call the dog, carnivore or omnivore, seem to matter so much to us? (And why do discussions about this issue seem to quickly escalate into shrillness, name-calling and spamming?)
First, let’s all just calm down. From a scientific viewpoint, it appears that some confusion may arise from the dual use of the term “carnivore”. This term is used as both a taxonomic classification and as a description of a species’ feeding behavior and nutrient needs. Both dogs and cats are classified within the taxonomic order of “Carnivora”, a diverse group of mammals that includes over 280 different species.
Some eat meat…..some don’t: While many of the species within Carnivora hunt and consume meat, not all are predatory or nutritionally carnivorous. The species within the order Carnivora vary considerably in the degree of dependency that they have upon a meat-based diet. For example, all of the cat species, including our domestic cat, Felis catus, are obligate carnivores. In contrast, bears and raccoons consume both plant and animal foods, while the Giant Panda subsists on a vegetarian diet. Therefore, while all of the species within the order called Carnivora can eat meat, their typical feeding behaviors exist along a broader spectrum, ranging from the obligate carnivores at one end to animals that are almost completely herbivorous at the other end.
So, where does the dog fall along this spectrum?
Cats vs Dogs: Let’s consider this question by comparing our two best animal friends, the dog and the cat. The label “obligate carnivore” (sometimes called true carnivore) means that the cat is incapable of surviving on a vegetarian diet and must have at least some meat (animal tissue) in its diet. This means that a diet that is composed of all plant materials cannot meet all of the cat’s essential nutrient needs. Specific nutrients that are problematic if Fluffy is fed a vegetarian diet include Vitamin A, a type of amino acid called taurine, and an essential fatty acid called arachidonic acid. All three of these nutrients are found in a form that cats can use in meat products and but are not found in plant foods. During evolution, cats either lost or never developed the ability to produce these nutrients in the body from the precursor forms that are found in plant foods.
The Adaptable Canine: In contrast, most of the canid species, including the domestic dog, are more generalist in their eating habits and subsequently in their nutrient needs. In the wild, wolves and coyotes exist as opportunistic predators, hunting and eating the type of prey that happens to be available. In addition to the flesh of their prey, wild canids readily consume viscera (stomach, intestines) which contain partially digested plant matter. Canid species also scavenge carrion and garbage and regularly consume fruits, berries, mushrooms, and a variety of other plant materials. Similar to its wild cousins, the domestic dog is a predatory species that also consumes plant foods and scavenges, and is capable of consuming and obtaining nutrition from a wide variety of food types.
Not only does the dog naturally choose a wider variety of foods to eat than do cats; the dog is capable of deriving needed nutrients from plant foods more efficiently than do cats. Let’s look at the three nutrients that we mentioned earlier; Vitamin A, taurine and arachidonic acid:
Finally, anatomically, dogs’ gastrointestinal tracts, from their mouths to their intestines, are consistent with other predatory species (i.e. meat-eating) that consume a varied diet. They have some ability to grind food (molars), and possess a small intestine that is longer in length (relative to body size) than that of obligate carnivores, but that is shorter in length than that of herbivorous species.
Altogether, the nutrient, metabolic, and anatomical characteristics of dogs place them on the omnivorous side of the spectrum within the wide range of species who hunt prey, scavenge, and consume plant foods
When we look at the evidence, we see that both nutritionally and taxonomically, the dog is best classified as an omnivore, an animal that consumes and derives nutrition from both animal and plant food sources. More specifically, the dog evolved from a species that made its living primarily through hunting and consuming prey but that also consumed whatever was available through scavenging. (Anyone who lives with a Golden Retriever is well acquainted with the scavenging part).
Time to drag out the box.
So, why is it that we read multiple websites, listen to certain “experts” and talk to Joe next door (who happens to know a lot about dogs) and they insist that the dog is an (obligate) carnivore? Why are some folks so incredibly (and one might venture, obsessively) invested in this belief? Not to put too fine a point on it, many proponents of the “dog as carnivore” hold on to this conviction like a dog with a meaty bone. One may wonder, why is this distinction even important, except perhaps for academic interest?
My own opinion is that the keen interest that we see in recent years is caused by an unusual and somewhat unprecedented focus on a desire to “feed dogs naturally.” Oddly enough, prior to the development of commercially prepared dog foods in the early 1900’s, domestic dogs were fed naturally – they were fed scraps of human food…..in other words, they scavenged. So, we appear to have come full circle, with the only difference being that the fervent adherence to a mantra of “feeding dogs naturally” now focuses on the dog’s hunting and meat-eating history rather than on its equally significant existence as a proficient scavenger.
Do dogs thrive on diets that include animal-based ingredients (i.e. meat, poultry, fish) – Yes, definitely (and especially if those ingredients are of high quality). Do dogs enjoy (and probably prefer) meat in their diets. Probably. Do dogs have a nutritional requirement for animal-based ingredients in their diets? No, they do not.