The Omnivorous Dog Part 1: Digestion of Plants

Is the dog an omnivore?  I guess is it depends on your definition of “omnivore’.

To most of us, an omnivore eats both meat and plants.  Alas!  This ‘definition’ is incorrect!

Any organism can eat any food, but whether or not a particular organism can reduce a food item to the point where nutrients can be extracted is an entirely different matter.  In the case of the omnivore, the ability to reduce plants to the point nutrients can be extracted is the wildcard.




Fun Fact For You:  There is no animal on the planet, visible to the naked eye, that is able to digest (and for our purposes, “digest” will mean reduce to the point nutrients can be extracted) plant materials.  Not even an herbivore has the ability to do this!

Specialized enzymes start to break down the rigid walls of plant cells, making them easier to consume – not by the animal who ate the plant – but the bacteria that reside in the animal’s digestive system.   These bacteria are the only animals in the world that have the ability to digest plants at the cellular level.

The herbivorous cow has both enzymes and plant eating bacteria in his saliva.  This means that at first bite, digestion of plant materials are well underway – not just reducing the size of food particles through chewing, but actual digestion of plant materials at the cellular level as food particles are coated with plant cell reducing agents.  Despite this jump-start, the cow has 4 stomach chambers – think of them as fermentation chambers – where massive amounts of bacteria feed on ever reduced food particles.  Even then, it’s not enough, ergo the cow’s ability to regurgitate stomach contents back to the mouth for further chewing /particle reduction (the term is rumination) which is then swallowed back down into the fermentation chambers. Enzymatic and bacterial action continue through the intestines right up to the point that ingested plant material becomes a cow patty on the ground.



The omnivorous human does not have the plant cell reducing powerhouse combinations of enzymes and bacteria of the herbivore.  For this reason, the human can only eat certain plant materials – fruits, vegetables, certain grains and roots, and others along those lines.  Enzymes, at the very least, and limited bacteria depending on the published research reviewed, starts reducing the plant material at the cellular (cell wall) level in the mouth via the saliva.  As the food particles are being reduced through chewing, they are also being coated with enzymes (possibly limited bacteria) which begins opening the plant cell walls for…  the bacterial population residing in the stomach.  By the time the plant material leaves the stomach, it’s pretty well broken down, but just to be sure, more enzymes and bacteria continue the digestion process in the intestines, ending at ….  well I think you can figure it out.




The omnivorous dog has no enzymes or bacteria in his saliva to start the process of digestion of plant materials.  He has no plant cell wall reducing enzymes or bacteria in his stomach.  Only at the point the food leaves the stomach and enters the intestines does any mechanism for the digestion of plant materials appear – enzymes and bacteria.  The food has passed through nearly half of the digestive system in a form (intact cell walls) that contributes absolutely nothing to the nutrition of the dog.  Not even the herbivore’s digestive system is efficient enough to digest all plant material when the process starts in the mouth with saliva, but we expect the “omnivorous” dog to be so efficient he can fully digest plant materials in the time it takes to pass through the intestines and exit the back-end.



The natural dog, free from human interference (think feral, not Fifi on the couch), tends toward 3 types of plant materials:

  1.  The stomach contents of prey.    These plant materials would be in various stages of digestion in the animal consumed. Enzymes and bacteria in the dog’s intestines would be able to do the ‘finishing’ digestion and extract nutrients from the plant materials.
  2. Rotting fruits and vegetables.  The cell walls of these plant materials are broken down through the process of decomposition.  The breakdown of the cell walls allows the intestinal enzymes and bacteria to extract nutrients from the material, however, significant nutrient loss has occurred through the process of decomposition.
  3. Fecal matter of herbivores.  Because no digestive system is 100 % efficient, partially digested food exits the back end of the herbivore.  Refer back to partially digested – all the intestinal enzymes and bacteria in the dog’s intestine have to do is finish the digestion.

OK, show of hands:  How many of you will chase down a rabbit, rot fruits and vegetables in the sun or collect Road Apples (the end result of horse digestion) to provide the plant materials most appropriate to your dog’s digestive abilities?  Anyone?



It’s much more civilized, socially acceptable and much less disgusting to stick to peas, carrots and green beans, isn’t it?  Bummer is, cooking them makes them more ‘digestible’ to the dog, but most of the nutrients leach out in the cooking process.  Raw is out of the question because the dog, more particularly the chemicals and organisms in his intestines, simply can’t extract enough nutrients to make it worthwhile.  Yes, you can grate raw, and more nutrients will be extracted, but it still falls short of nutritional requirements.

If all one considers is the presence of plant material specific enzymes and bacteria in the digestive system, yes, dogs are omnivores.  However, a more correct description would be that dogs are Limited omnivores.  The dog has no ability to extract sufficient nutrients from plant materials to survive on a diet of plants alone or as the majority of the diet unless those plant materials are highly processed, so much so that they have lost all or most of the possible nutritional value.  No one knows this as much as those who feed their dogs vegetarian or vegan – just look at their collection of supplements!

We’re going to continue the discussion of the omnivorous dog through his macro nutrient requirements in the next installment.  I just want you to consider what I’ve said here and how it applies to how and what you feed your dog.  I also want you to do a little research:  Look up digestion of the cow and human, 2 critters that have been studied extensively without political, moral or marketing bias.   You can’t do the same lookup for dogs because most of our Internet available information is based on a belief that dogs didn’t eat before the creation of commercial dog food where plant materials passed meat as the dominant ingredients.  I’ll give you some resources later on, once we have finished our discussion of the omnivorous dog.


Until then….

Humans and dogs have existed separate and together for millennia and tales of friction are legion.   Can we all agree that stories of feral dogs, either individually or in packs, taking down small or baby livestock is the primary complaint?  If dogs are natural and human-like (more efficient) omnivores, how come there are no accounts of packs of feral dogs taking out crop fields?  Think about it.