Sunday, June 6, 2010

Do Wolves/Dogs Eat the Vegetable Contents of Herbivores' Stomachs?

A major argument to justify vegetable matter in dogs' diets is the claim that wolves eat the stomach contents of their herbivore prey. The stomach contents of wild herbivores are partially digested and undigested gasses.

Do wolves, in fact, eat the stomach contents of prey? Not according to David Mech (1), who has studied wolves in various parts of the world for more than 30 years. Mech observed wolves attack large herbivores, such as moose and elk. When wolves open the abdominal cavity and begin to eat digestive organs, they shake out the contents of stomachs before eating the organs. Thus, according to Mech, wolves eat a small amount of  digested grasses that cling to the rough lining of stomachs, but they shake out large volumes of undigested grasses from herbivores' stomachs.

I feed my dogs green tripe, as well as many other raw meats and meaty bones. Green tripe is the stomach of cattle that, when grass-fed, closely resembles the stomachs of wild herbivores. Fortunately my dogs eat  grass-fed beef from local ranches.

I noticed a curious phenomenon: When first handed a whole green tripe, my dogs shake it, before settling down to eat it. Why on earth would they shake green tripe? There is nothing inside the tripe to shake out. It's contents were shaken out at the meat-packing plant. The dogs don't shake other meats, even other organ meats, such as heart, kidney, lung, and spleen. They shake only green tripe.  Yesterday, I asked a friend to take rough videos of the phenomenon with my small digital camera.  The quality is not good, but the dogs' behavior is clear.  As I handed dogs green tripe, he filmed what they did with it.  Here's the video.

My hypothesis about shaking green tripe is that dogs and wolves are hard-wired for the behavior  Dogs are hard-wired for certain behavioral sequences in hunting and shepherding.  The Coppingers (2) detail the selection of dog breeds for specific, hard-wired behaviors.  Before you become outraged over genetic determinism, I hasten to add that all mammalian behaviors have learned elements.  Dogs must be raised with sheep to become good shepherds.  Hunting dogs need early experience on hunts to develop their hunting skills.

Natural and artificial selection for specific behaviors simply predispose some dogs to show the behavior and to learn the behavioral sequence more readily than other dogs.  Here's an important caveat: The desired behavior must appear spontaneously, before it can be reinforced with experience.  If the dog never shows the behavior, there is nothing to reinforce, and the dog cannot learn how to use the behavior. So, gene-based wiring for a behavior to appear at some point in development is essential for continuing and shaping the behavior.

In an earlier blog entry, I cited a specific Labrador retriever behavior that was selected in a breed specialized for bird hunting: Dogs dive into the water to retrieve ducks and geese, and when they return are pulled into the boat by other dogs, thereby allowing the hunter to continue firing.  The behavior of pulling other dogs from water shows up inappropriately when my Labs try to pull each other out of the swimming pool -- a behavior that is not much appreciated by other dogs.  Yet, they are "driven" to do it.

I think wolves and dogs evolved to shake the contents from ruminant's stomachs before eating the organs.  Carnivores are not equipped to use vegetable matter as food, unless the vegetable matter is predigested.  Digested grasses that cling to the stomach lining of green tripe are perfect for wolves and dogs' diets.

When confronted with an herbivore stomach, dogs shake it, even though the green tripe is empty.  It's curious to observe behaviors that have no function in their present context.  The fact that they appear at all suggests they were hard-wired in evolution.

The implication of this discovery is that wolves and dogs do not need or want large amounts of vegetation in their diets.  They are carnivores who eat prey.  A little bit of digested veggies is sufficient.

(1) L. David Mech & Luigi Boitani (Eds.) Wolves: Behavior, Ecology, and Conservation,Chicago: U. of Chicago Press, 2003.
(2) R. Coppinger & L. Coppinger, Dogs: A New Understanding of Canine Origins, Behavior, and Evolution, Chicago: U.of Chicago Press, 2001.
It is most unfortunate that the Coppingers' book was written before wolf and canine genetic mapping was completed.  They exaggerate genetic differences between dogs and wolves.  Their observations of wolf and dog behaviors, however, are extremely valuable.


  1. I'm looking to get a dog soon and I'm putting him or her on the raw diet so this was very informing. Don't you love a real comment and not spam :)