Why Dogs Chew
By Myrna Milani, BS, DVM
(Originally written for DogWatch, a newsletter for the general public from the Cornell University College of Veterinary Medicine)
My dog, Duffy, seems to enjoy chewing, just for the sake of chewing. He chews a variety of toys and even some gum my son once dropped on the floor, but he's not destructive. Sometimes he wears such an unusual look on his face when he chews, I can't help wondering what's going through his mind.
Even though all animals must eat to survive, we know surprisingly little about mouth-related behaviors. However, we do know that many mental as well as physiological factors come into play. For the sake of convenience, we can view chewing behavior in dogs as part of a continuum that includes sucking and licking at one end and biting, tearing, and chewing at the other.
Although we typically think of canine teething as the process whereby adult teeth replace deciduous (baby) ones by about six months of age, pups experience continual mouth-related behavioral changes from their toothless birth until they reach full adulthood. Moreover, in the average pet those behaviors comprise a composite of wild, domestic, breed, and individual characteristics. Add how the dog's relationship with the owner and environment also may affect how these play out in a particular setting, and we can appreciate how deep and complex the roots of Duffy's chewing could be!
Like wild dogs, domestic dogs initially get nourishment from their mothers in the form of milk, and toothless sucking at this stage confers two advantages. One, a lack of teeth makes it easier for the pup to create the vacuum necessary to draw milk from the mother's breast. Two, toothless gums pose less of a threat to delicate nipples, a real plus because infected nipples can lead to infected milk glands (mastitis) and undermine the health of both the mother and the pup.
As their baby teeth grow in and mature, pups make the transition from milk to solid food and experience the behavioral changes that go with that. Instead of sucking, they pick things up and carry them around, chew on their mothers' ears and tails, jump on their litter mates and grab them by the neck. Mastering these gentler mouthy behaviors later enables adult animals to carry objects (including their own pups), play, and mate without harming the objects of their attention.
Because adult teeth enable the dog to hold and kill prey, then to tear, chew, and grind it up, their emergence signals another shift in the pup's mind set. Mouth-holds become much more powerful and any resistance causes the animal to bite harder rather than let go. Whereas too hard a bite to a member of its own species could result in discipline from a superior or loss of a playmate or mate, not hanging on to prey firmly enough could cost the dog a meal.
From this we can see that the domestic dog comes prepackaged with a full spectrum of wild dog mouthiness. However, in addition to this, domestic breeding comes into play. Humans found lap dogs who sat in their laps and lapped them more worthy of breeding than those who bit them. When people wanted dogs to retrieve but not crush fragile birds and other game, they bred velvet-mouthed animals who would hold gently rather than clamp. Those who wanted dogs for herding bred nippers who inflicted just enough of a bite to keep a reluctant sheep moving, but not enough to harm it. Humans who felt the need of canine protection selectively bred those animals known to bite hard.
Where wild dogs and domestic ones who actually perform their in-bred function live in a world where a checks-and-balance system ensures these animals display the right kind of mouthiness at the right time, the average pet may wind up with a lot of mouthiness and no idea what to do with it. Put that pet in a stressful environment with no owner guidance and it may combine the pup's desire for a comforting chew on mom with the predator's force and wind up destroying the owners' belongings to relieve any tension. With proper owner guidance, though, many dogs learn to use chewing not only to relieve stress, but also just to enjoy themselves, the same way we humans might sip a relaxing cup of tea.
When Duffy leisurely chews with that faraway look in his eyes, could the activity evoke ancient memories of the wild dog gnawing on a choice bit of prey with his packmates? Or could the chewing remind him of the times he chewed his mother's tail after he nursed? Better yet, could he be pondering how much fun he had playing fetch with his owner that morning?
Until we learn to think like dogs, we can only guess what goes through Duffy's mind during these idyllic interludes. Chances are, though, that contentment plays a role in it.