Dog and Cats are omnivores? This myth has a corollary in “dogs and cats have evolved into omnivores” and “cats and dogs are obligate scavengers’” myths. This myth is another perpetuation where if the facts don’t fit the theory, change the facts. Species behave in their own way, regardless of its genetic similarity to some other species. For a longer or shorter time, the species “dog” has been living in its own ecological niche and has become adapted to that niche. No matter what it started out as, and no matter when it stopped being a whatever else it was, the dog is now a dog, a facultative carnivore.
Let’s contextualise the role and importance of digestive enzymes for starch and other plant materials, and important point when considering the basis of this myth. Neither cats, nor dogs, unlike omnivores, have the enzyme, amylase, in their saliva. Amylase is required to begin the breakdown of carbs in the mouth – that first bite. This is required since the metabolism of carbs takes a long time! Let’s rephrase … the “omnivorous” dog has no enzymes or bacteria in his or her saliva to start the process of digestion of plant materials. He or she 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 or cat. 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 and cat to be so efficient he or she can fully digest plant materials in the time it takes to pass through the intestines and exit the back-end.
The herbivorous cow has both enzymes and plant eating bacteria in his saliva. This means that at first bite, digestion of plant materials is 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 (four) 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.
That the “omnivorous” dog physiologically tends highly carnivore (their teeth are designed for: “…are designed for grabbing, ripping, tearing, shredding, and shearing meat”1 , due to his digestive abilities and nutrient requirements, has been known since the dog was first used as a laboratory animal. The earliest published scientific paper we have been able to find stating this was written by Cowgill, G. R., 1928: “The energy factor in relation to food intake; experiments on the dog“. Amer. J. Physiol., 85, 45–642 . The pet food industry, AAFCO, the US National Research Council (NRC), all serious textbooks and reference material provided to hopeful vet school students … none deny that carbohydrates are not required by the dog. It is also agreed that the most efficient source of all required nutrients is animal tissue. Despite these facts agreed to by all, commercial McKibble and McCan continue to sell pet parents, guardians and slaves on the concept that the dog (and cat) is an omnivore! Please read the related post(s) to gain more insight into the topic.
References and Research
- 1.Mammalogy: Adaptation, Diversity, and Ecology. 2nd ed. McGraw-Hill Science/Engineering/Math; 2nd Edition (June 18, 2003); 2003. https://www.amazon.com/Mammalogy-Adaptation-Diversity-George-Feldhamer/dp/007290948X