Carnivores or Omnivores

DOGS!

OMNIVORES OR CARNIVORES

YOU DECIDE!!

Veterinarians learned that cats are carnivores; horses, rabbits and ruminants (cattle, sheep, antelopes, deer, giraffes )are herbivores; and pigs and dogs like people, are omnivores. After attending a nutrition conference an audience of 300 plus nutrition researchers and veterinary professionals were treated to a strong argument in favor of dogs as carnivores. Urging us to rethink the “dogma” of dogs as omnivores, Dr. Wouter Hendriks of Utrecht University’s veterinary school in the Netherlands laid out a detailed and ultimately convincing argument in favor of canine carnivorous-ness at the Waltham International Nutritional Sciences Symposium in Portland, Ore. We’ve been studying the dog’s nutritional needs for a hundred years or more now. Why the sudden shift in thinking on something that seems so basic?

The Omnivore Angle

The answer is not so simple, but to understand how we might’ve been led astray, it helps to explain the science behind the omnivore “dogma.” To that end, here are three points in favor of the canine-as-omnivore theory:

1. Intestine size. Because meat is relatively easy to digest, the intestinal length of carnivores like cats is relatively short. Plant material is more difficult to break down, so herbivores have much longer intestines. And dogs, like omnivores, fall somewhere in between, with an intestinal length just slightly longer than the cat, so it makes sense that dogs might be classified as omnivorous in this issue.

2. Wolves eat grains too. The story goes that the dog’s wild ancestors ate plenty of grains. It’s said not only that wolves will indulge in the occasional berry but that they’ll binge on grains contained within their prey’s stomach.

3. Dogs are especially adapted to eating grains, anyway. It was recently found that dogs are different from their wild cousins in that they have three genes related to starch and glucose digestion. As such, it’s hard to deny that dogs are especially adapted to eating grains and other vegetation.

The Carnivore Perspective

Given these fine points, it makes sense that we might rightly consider a dog an omnivore. But it’s apparently not so cut and dry. Consider Dr. Hendriks’ rebuttal to the above:

1. Coefficient of fermentation.

It’s not about intestinal length, says Dr. Hendriks. In fact, when you figure in the wider girth of the feline intestine, the total volume of canine and feline intestines are actually quite similar. But when comparing animals' gastrointestinal systems, it might be best not to think about length, girth, volume, capacity or any of that. It might be more appropriate to look at a metric called the “coefficient of fermentation.” Herbivores have a high ability to extract nutrition from plant matter as the result of their ability to ferment it, and therefore have a high coefficient of fermentation. Carnivores aren’t equipped to do this and therefore have a low coefficient of fermentation. Interestingly, the coefficient of fermentation is similarly low in both dogs and cats.

2. The wolf myth.

Wolf researchers have concluded that wolves are clearly carnivorous. The current literature demonstrates that foraging is a tiny percentage of a wolf’s intake, and that wolves tend to leave stomach contents behind after a kill. Furthermore, a literature review in search of the source of the idea that wolves feast on stomach contents came up empty. Dr. Hendriks’ conclusion? It’s a myth. It’s not based on systemic observation.

3. Dogs have adapted well… but that doesn’t make them carnivores.

In the fifteen thousand years it’s now believed dogs have lived beside humans, they’ve evolved. So, too, have humans. We’ve shifted from that Paleolithic, hunter gatherer diet to one that reflects a way of life condition. In the case of dogs, we’ve found a few genes that reflect this adaptation. So, too, have we found genes that indicate a neurologic adaptation to cohabitation with humans. But just a few genes’ difference is regarded as an adaptive shift to a condition. These alone can’t possibly alter the entire digestive evolution of a species. Indeed, dogs still have plenty of traits that are 100 percent carnivorous: Dogs’ teeth are adapted to a carnivorous diet (for tearing muscle and crunching bone to extract marrow). Many of their innate behaviors are carnivorous in nature. Consider digging, for example. Like wolves, dogs dig to hide parts of meals for future ingestion. Dogs, like many large mammalian carnivores, are metabolically able to survive for long periods of time between meals. Dogs have a lot of flexibility in metabolic pathways to help make up for a feast-or-famine lifestyle and a wide range of possible prey. The result of these findings, argues Dr. Hendriks, is that the dog is undeniably a true carnivore. The dog just happens to have an adaptive metabolism as a result of living with humans for millennia. That’s why the dog is perfectly capable of eating a grain-based diet, as most commercially fed dogs do.

Why It's Important

But the issue is this:

Just because dogs are a domesticated species with an adaptive metabolism that allows them to cope with life as an omnivore doesn’t mean they’re not true carnivores. Accepting “this explanation derived from feeding ecology,” offered Dr. Hendriks in his final statement, “helps to improve our understanding of the dog’s digestive physiology and metabolism and may contribute to the ongoing optimization of foods for our pet dogs.” But that doesn’t necessarily mean we’ll be moving away from a grain-based diet for most dogs anytime soon — in fact, most will probably never experience the potential benefit of what may be a more biologically appropriate diet. Nonetheless, knowing what a dog’s ideal diet looks like is the foundation of any nutrition program.

DR. PATTY KHULY VMD

Welcome to the Age of Choice

In spite of their natural carnivorous design, dogs have still managed to evolve over thousands of years… surviving on the meat and non-meat scraps and leftovers of human existence. So, over time, dogs have proven to be fully capable of thriving on a variety of foods. Today, the dog food marketplace has become a living, breathing witness to the animal’s adaptive ability… and is abounding with an astonishing array of product designs. Some favor meat. Some feature vegetables. And others are made almost entirely of cereal grains and beans; So, how do you choose the right one for your pet?

The Bottom Line

Knowing that dogs are optimized for eating meat can make it easier to recognize better dog foods. Even though dogs do demonstrate a notable omnivorous capacity, we believe it’s important to give preference to meat-based products.

That’s because…

Whether you believe they’re carnivores or omnivores, dog’s possess an undeniable carnivorous bias Meat-based dog foods are closer to a dog’s natural ancestral diet. They’re more like the real thing. Footnotes So! Are dogs carnivores… or omnivores? The Great Debate goes on. And on. When it comes to choosing dog food, it’s important to know the answer to that question. So, if you’ve already been told dogs are indifferent omnivores with no natural preferences…Or that they’re strict carnivores with an innate aversion to eating fruits and vegetables… All scientific evidence clearly points to the fact that… Dogs have a natural carnivorous bias. From DNA studies, we know dogs evolved directly from the wolf somewhere around 15,000 years ago. And, of course, it should come as no surprise. Wolves are clearly carnivores. So, by their very genetic pedigree, dogs also demonstrate similar and noticeable carnivorous traits. Their teeth, their digestive systems and their behavior clearly confirm this fact. Yet dogs must also be recognized for their significant omnivorous ability. Their proven ability to digest carbohydrate-based foods has been known for many years. After all, modern genetic research has proof that ten canine genes play key roles in starch digestion and fat metabolism. However, a dog still shows unmistakable evidence that its body is optimized for eating meat.

Dogs Don’t Grind… They Chop

For comparison, think about a typical herbivore… a dairy cow. Picture the way they “chew their cud”. Cows chew widely from side-to-side. And they have broad, flat back teeth. And flat teeth are ideal for grinding grains and plant material into finer particles. True omnivores (like humans) share this same combination of boxy back teeth and sideways grinding motion common to herbivores. Think of your own mouth and how you chew. Dogs, on the other hand, don’t have flat teeth. Like all carnivores, they have narrow pointy back teeth. Plus dogs can’t chew from side-to-side. Their jaws can only move in an up-and-down, chop-chop motion. It’s the perfect combination for cutting meat into smaller chunks.

No Salivary Amylase

Herbivores and omnivores possess one aid to digestion carnivores typically lack. Carnivores do not produce amylase in their salivary glands. Amylase is a specialized enzyme most herbivores and omnivores produce in their saliva. It helps begin the break down of starchy carbohydrates into simple sugars… before they enter the stomach. Although dogs do produce amylase, the enzyme is added further down the digestive tract… in the pancreas and small intestine.

Digestive Anatomy

Since they consume fewer but larger meals, carnivores have bigger stomachs than their grazing, plant-eating counterparts. What’s more, meat-eating animals exhibit a higher concentration of stomach acid. This allows faster digestion of animal protein. The stronger acid kills the disease-causing bacteria abundant in decaying meat. What’s more, herbivores have an unusually long gastrointestinal tract… exceeding ten times the animal’s body length. Longer systems like this are needed for consuming a plant-based diet.

A Dog’s Ancestral Diet vs. Today’s Kibble

So, what should the nutrient content of a dog’s diet look like? Well, let’s compare a dog’s natural ancestral diet with the nutrient content of a typical dry dog food… Notice the higher carbohydrate content of the kibble compared to the dog’s natural ancestral diet, and the dramatically lower protein and fat. These two feeding profiles are nowhere near alike. So, using a natural ancestral diet as a benchmark, doesn’t it make sense for a dog’s diet to be more balanced? A dietary design that includes…More protein, More fat, Fewer carbohydrates.

The Bottom Line

Keeping in mind this picture of the ideal dog food, here are seven characteristics you may wish to look for when shopping for a good dog food…

1. Higher in quality meat-based protein

2. Higher in natural fats and oils

3. Lower in carbohydrates

4. Formulated from a named (non-generic) animal source

5. Free of artificial flavoring, coloring or preservatives

6. Complete in all essential vitamins and minerals

Lindblad-Toh K, Wade CM, Mikkelsen TS, et al, “Genome sequence, comparative analysis and haplotype structure of the

domestic dog”, December 2005, Nature 438 (7069): 803–19

Axelsson E. et al, The genomic signature of dog domestication reveals adaptation to a starch-rich diet, Nature, 2013 Jan 23,

doi: 10.1038/nature11837, Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, 75237 Uppsala, Sweden

Animal Health Diagnostic Center, Cornell University School of Veterinary Medicine

11/17/2014 Removed: “So, without salivary amylase, a dog’s carbohydrate digestion can be decidedly more difficult.”

There has long been debate as to whether the dog is a carnivore or an omnivore. The National Research Council of the National Academies and some larger dog food companies consider dogs as omnivores. However, most holistic veterinarians believe dogs are carnivores. All mammals have evolved over time to maximize their survival and have adapted physically to their environment in order to optimize their health and survival. So before deciding whether the dog is an omnivore or a carnivore, it’s important to first look at the unique physical features that their evolution has created.

The Gastrointestinal System

Since we’re talking dietary evolution, the gastrointestinal system is the most obvious adaptation to start with. The digestion of a plant based diet is by nature very different then the digestion of a meat based diet. Plants contain quite a bit of cellulose and starches. In order to break these materials down, the body requires unique digestive enzymes as well as the proper dentition to grind and break down these large components. Amylase and cellulase are the digestive enzymes a body needs to convert plant based starches and cellulose into sugars, which can then be absorbed by the small intestine, or in the case of cellulose, further fermented to develop usable food macronutrients. Herbivores and omnivores secrete amylase in their saliva to begin the breakdown of starches into glucose as soon as the plant enters the mouth. Because carnivores eat very little plant food, they haven’t adapted to produce salivary amylase. Cats and dogs don’t produce salivary amylase.

Dentition Adaptation

The size, shape and dentition (the way the teeth fit together) of an animal’s mouth have also adapted to fit their diet. Herbivores, such as horses and cattle, have long, large, wide molars with flat surfaces to allow for proper grinding of their high fiber plant source diets. This grinding breaks down plant material into smaller, more usable matter. The incisors of herbivores are designed to pick the plant material, such as grass. The long tongue then pushes the grass to the inside back of the mouth for grinding by the very strong and efficient molars. The final, mechanically ground food is then swallowed for further digestion. The dentition of a carnivore is very different, however. The carnivore teeth are designed to rip and tear meat from the bone and then gulp it down for further digestion in the stomach. The canine teeth are long, pointed and sharp to allow deep penetration into the prey. The teeth also have a tight inter-digitation to lock in place to allow the carnivore to rip the flesh away from the prey. There is little to no grinding – the meat is mechanically broken down by only two or three chomps of the molars before the food is swallowed. Dogs and cats possess these long canine teeth and tight digitation of the molars. To better understand the difference, the teeth of the omnivorous human more closely reflect the herbivore teeth with short canines and large strong molar arcades that allow for the grinding of fruits and vegetables.

Length of the GI tract

As we proceed down the path of food digestion, the differences between the species are even more apparent. Herbivores have the longest GI tracts, at about 100 feet in length. Their GI tract includes areas for the fermentation of cellulose, which is difficult to break down. Even after the mechanical breakdown of grasses by the grinding teeth and salivary amylase, and the further breakdown by the stomach acid and its digestive enzymes, the cellulose may still need to be fermented in the rumen or the cecum. Omnivores such as humans have medium length GI tracts of about 20 to 40 feet. The appendix is actually the remnant of a fermentation system in the large intestine. Cats have the shortest GI tracts of all the species, at 12 to 15 inches. This is because carnivores typically eat easily digestible food such as meats. The canine GI tract is also quite short, at about two feet. This is drastically shorter than the herbivore but also much shorter than the omnivore. Neither the cat nor the dog has an area of the GI tract where the fermentation of cellulose can take place. A carnivore wouldn’t need it.

Omega-3s

All animals need Omega-3 fatty acids to support health. An Omega-3 fatty acid is considered an essential fatty acid, meaning the animal’s body doesn’t produce it, so it needs to be consumed. There are both vegetable and fish based

sources of Omega-3. Vegetable based sources of Omega-3 are in the form of alpha-linolenic acid, known as ALA. ALA is found in green leafy vegetables as well as flax, hemp, chia and other plant oils. The ALA needs to be converted to eicosapentaenoic acid, EPA, and docosahexenoic acid, or DHA. EPA and DHA are the active forms of Omega-3 fatty acids. Herbivores and omnivores can convert plant based ALA sources to EPA and DHA through a series of enzymatic reactions. Cats, however, completely lack the enzymes necessary for this conversion, and dogs can only convert approximately 5 to 15 percent of the ALA sources.

Omnivore or Carnivore?

Although they differ somewhat from cats, dogs should be considered carnivores based on their dentition, as well as the length of their canine teeth. A dog’s teeth reflect the mechanics of the ripping and tearing of food. They also possess a shortened gastrointestinal tract, versus the longer GI tract of an omnivore or herbivore. In addition, dogs don’t have amylase, an enzyme that breaks down sugars, in their saliva, like an omnivore and herbivore would have. The relative inability to convert plant based sources of Omega-3 fatty acids into EPA and DHA is also a strong indication of carnivore status. Based on their digestive tract adaptations, I believe that dogs are scavenger carnivores, while cats are true carnivores. A scavenger is an animal who will sort through discarded material or eat dead carcasses to take advantage of what it finds. Although dogs would prefer meat, they can survive on whatever is available.

Angelica McLoughlinJune 3, 2021