Are dogs true carnivores? 🍖

Carnivore, herbivore, omnivore; the three classifications of animal diets. Many people consider dogs to fall under the carnivore category, but is this really true? In recent years, there has been a boom in the promotion of raw diets, with raw pet food manufacturers claiming that because dogs share “99% of its DNA” with the wolf, it should be fed the same. Dogs do generally prefer the taste of meat over plants but this does not mean that they do not benefit from plants in their diet as well. Let’s take a walk through dog evolution and take a look at what might make dogs a little different than a true carnivore species.

The beginning

Genetic dating has taught us that the genealogical link to the modern day dog is the wolf. Undeniably, wolves are a carnivorous species and absolutely require meat to survive but your contemporary canine companion is a little bit different than its ancestral counterpart.

Dogs were first domesticated approximately 15,000 years ago. Canids would enter human camps in search of food and slowly became accustomed to human interaction. Since then, dogs have evolved and changed greatly in the last 15,000 years and one major alteration is their diet. 

Dog morphology

Through selective breeding, dog morphology and physiology has greatly evolved. From the wild wolf in the forest to the nap loving dogs we see today, there are quite a few differences in how these canids function. The changes are quite clear (refer to image below).

The first and probably most notable change is to body size. Wolves are large creatures, designed to take down equally large prey. An animal the size of a wolf would have been a lot more difficult for humans to control during early domestication. As a result, the dog was selectively bred to be smaller and more manageable for feeding and training. This takes away some of its ability to hunt large prey like wolves do.

Many of the modern breeds have shorter, broader snouts than the wolf. This trait was selectively bred for aesthetic or working purposes and less so for hunting prey and foraging. Similarly, certain breeds have lost the perky, uprite ears of the wolf and traded them in for floppy ears that can be used for scent detection. Some breeds, like German shepherd and husky still carry some of the token wolf traits and are considered to be more closely related to the wolf.

Even with a different snout shape, dogs still have the same number of teeth as wolves do. However, those 42 teeth, along with the skull and jaw, are larger and stronger in the wolf than the dog. Dr. Huges, a veterinary geneticist at Wisdom Health, says “this is likely due to their need to bite and break things like bones in the wild, compared with dogs who evolved much more as scavengers of human refuse”.

Arguably the most important difference between wolf and dog nutrition is gastrointestinal morphology. Dogs have evolved to eat what humans eat and this means that the dog’s GI system has also evolved. Dogs can no longer process raw, wild meat without concern for microbial and parasite contamination. Unlike wolves, dogs can also not go days without eating and are accustomed to regular, daily feedings. This means that the high protein, high fat diet that wolves eat will provide them with enough energy to survive several days without food, something that domestic dogs just don’t need. A dog on a high fat, high protein diet, without the balance of a rigorous exercise regime is more likely to become obese.

Dog digestion is also a little different from that of the wolf. Dogs are more genetically equipped to digest starches and produce longer chain starch-digesting enzymes than wolves do. This means that it is easier for dogs to break down and absorb starch sources like potatoes, rice and peas. 

Swedish scientists at the University of Uppsala sequenced the genome of both the dog and the wolf. The researchers found that 36 genes differed between the dog and the wolf, with 10 of those being genes involved in starch digestion and fat metabolism. The mutations that were found were determined to aid the total digestion of starch and fat in dogs relative to wolves.

Overall, the adaptive and morphological differences between the dog and the wolf demonstrate that dogs are indeed equipped to handle plants and carbohydrates in their diet.

Digestibility of starch

Digestibility is the measure of how much of a specific nutrient is digested and absorbed in the gastrointestinal tract. This helps to estimate how nutritious certain diets and certain nutrients are to dogs. Various studies have shown that carbohydrates and starches are moderately digestible by dogs and do contribute to a dog's overall nutrition.

Salivary amylase is the first enzyme that catalyzes the breakdown of dietary starch. Unlike humans, dogs lack this enzyme and must rely on the small intestine for the breakdown and absorption of carbohydrates. Simple dietary sugars can be easily absorbed without much breakdown, while more complex carbohydrates require hydrolysis from enzymes, such as pancreatic amylase. 

Ground, cooked and extruded starches are almost 100% digestible to dogs, while the digestibility of uncooked starches varies from 30-65%, depending on the type of starch. This is part of the reason why dog kibble is most often extruded. Processing makes carbohydrates more digestible for dogs.

Lastly, undigested carbohydrates move from the small interesting to the large intestine, where complex starches undigested by pancreatic amylase, are fermented and broken down by microbes. This is part of the reason why it is important for dogs to maintain a healthy microbiome. Microbes also produce short-chain fatty acids from the fermented staches in the dog’s colon. Fatty acids help to absorb important minerals, including calcium, magnesium, and iron.

The debate

So, does this mean dogs are carnivores or omnivores? Actually they are neither. Dogs are considered obligate carnivores. This means that while dogs do need meat to survive, they can also benefit from plants in their diet as well. Since dogs can digest carbohydrates, they can benefit from the energy, vitamins and minerals that plants contain. Ultimately, just because your dog is descended from a true carnivore, does not mean that it needs to be fed like one.

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References

Kendall Curley. “8 Differences Between Dogs and Wolves.” (2018). https://www.petmd.com/8-differences-between-dogs-and-wolves-0

Axelsson, Erik, Abhirami Ratnakumar, Maja-Louise Arendt, Khurram Maqbool, Matthew T. Webster, Michele Perloski, Olof Liberg, Jon M. Arnemo, Åke Hedhammar, and Kerstin Lindblad-Toh. "The genomic signature of dog domestication reveals adaptation to a starch-rich diet." Nature 495, no. 7441 (2013): 360-364.

Hejjas, Krisztina, Judit Vas, Eniko Kubinyi, Maria Sasvari-Szekely, Adam Miklosi, and Zsolt Ronai. "Novel repeat polymorphisms of the dopaminergic neurotransmitter genes among dogs and wolves." Mammalian Genome 18, no. 12 (2007): 871-879.

Wayne, Robert K. "Evolutionary genomics of dog domestication." Mammalian Genome 23, no. 1-2 (2012): 3-18.

Murray, S. M., E. A. Flickinger, A. R. Patil, Neal R. Merchen, J. L. Brent Jr, and G. C. Fahey Jr. "In vitro fermentation characteristics of native and processed cereal grains and potato starch using ileal chyme from dogs." Journal of animal science 79, no. 2 (2001): 435-444.

Moore, M. L., H. J. Fottler, G. C. Fahey Jr, and J. E. Corbin. "Utilization of corn-soybean meal-substituted diets by dogs." Journal of Animal Science 50, no. 5 (1980): 892-896.

Silvio, Jennifer, David L. Harmon, Kathy L. Gross, and Kyle R. McLeod. "Influence of fiber fermentability on nutrient digestion in the dog." Nutrition 16, no. 4 (2000): 289-295.

Kienzle, E., B. Dobenecker, and S. Eber. "Effect of cellulose on the digestibility of high starch versus high fat diets in dogs." Journal of animal physiology and animal nutrition 85, no. 5‐6 (2001): 174-185.

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