Aggression is probably the most common reason an otherwise healthy dog is euthanized (put to sleep). We sometimes forget dogs are predators and can inflict serious and even fatal wounds. A truly aggressive dog is terrifying -- and rightfully so.
You need to understand if your dog is really displaying aggression. The word aggression has a specific meaning in the field of animal behavior. It's also relative: What would be aggressive to us may be perfectly ordinary to a dog. A good example is play. A child who chased another child across a field, bit him on the back of the neck, and pulled him down to the ground at a dead run would be acting pretty aggressively. However, to a pair of playing dogs, that's an accurate description of a good time. Play is often viewed as practice for real-life skills, so it's not unusual to see stalking, chasing, hunting, and even killing behaviors as part of normal dog play.
So how can you tell? Usually by the look and sound. Does the dog have a play face (wide-open eyes and relaxed-open jaws, like a big, toothy grin)? Is the behavior accompanied by furious or loud snarling and barking? Or is it play-growls and happy yips? A surefire sign is if the roles reverse: If there's a chase on and suddenly the chasing dog changes direction and is being pursued, you can bet it's play.
There are several reasons why your dog may display aggressive behavior. Here are the types of aggression.
Defensive. Here's a classic scenario for defensive aggression: The dog does something wrong; the owner catches the dog and scolds him; the dog then retreats under the bed; the owner reaches under the bed to pull the dog out and reprimand him for the misdeed; and the dog bites the owner.
Any dog will bite when he feels threatened. In this case, the dog gave ground and made himself "invisible," which is submissive behavior in dog society. The only reason the dog could think of to explain why the owner was still pursuing him after he had submitted to the owner's dominance was the owner intended to do him harm. So the dog protected himself. The best thing to do if your dog retreats is to just leave him alone.
Territorial. Territorial aggression is one of the reasons we like living with dogs. They will defend their territory -- which can include our home, our possessions, their food, and us -- against all comers. Without territorial aggression, there would be no watchdogs.
But territorial aggression can get out of hand. It can pop up in things as minor as jumping up, as frustrating as marking territory, or as serious as biting. Again, a good dominance relationship with your dog is crucial. If you're the dominant dog, he'll feel secure when you feel secure -- and won't defend territory against friendly visitors, meter readers, and letter carriers -- but will still defend you and your home when the need arises.
Agonistic (pain-related). A sick or injured dog knows he is vulnerable. The same is true for an aging dog, whose senses have dulled, reactions have slowed, and mobility has decreased. Even ordinary situations can make a vulnerable dog feel the need to lash out in his own defense.
Sometimes the dog's pain is obvious, and you can be ready for possible aggression. Other times, however, it's not so easy to tell until it's too late. If you're petting or playing with your dog as usual, for example, and he suddenly growls or snaps at you, you should suspect something hurts and call the vet right away. Arthritis is a common cause for this type of behavior.
Reproductive. This one probably needs no explanation. If there's a female dog in heat anywhere in the known universe, unneutered male dogs know it and will try to get through everything -- including each other -- to reach her. The drive to reproduce can trigger fighting with other dogs and even uncharacteristic aggression toward family members.
The surefire solution for this type of aggression is obvious but important: You must neuter or spay your dog, preferably before the age of six months.
When to Call the Vet
Aggressive behavior isn't something that can be ignored or laughed off. Your dog's life depends on it. If your dog is launching serious attacks, especially without warning or provocation, get him in for a thorough veterinary exam as soon as possible. Your vet can help you determine a course of treatment or refer you to a competent behaviorist. Though aggression can sometimes be related to a physical problem, such as a brain tumor, encephalitis (infection of the brain), lead poisoning, low blood sugar, or liver disease, it is usually a behavioral problem. If your dog shows any form of aggressive behavior, call your vet or an animal behavioral specialist immediately.
One of the most characteristic types of aggressive behavior in dogs is biting -- something we dread whether we own a dog or not. We cover this behavior in the next section.