Rivalry can occur between dogs living in the same household and is characterized by repeated conflicts between them. These conflicts may initially involve growling, snarling or snapping, but they can build to serious, and potentially dangerous, fighting.

Rivalry occurs because animals who live together establish a dominance hierarchy, or a social structure within their group. If that hierarchy is not stable, if there is uncertainty or contention about the ranking or social position of each dog, then conflicts may arise. There are many reasons why this may occur, including the recent introduction of a new animal in the house, the death or removal of an animal, or the return of an animal after an absence. Problems may also occur when social maturity is reached by a young, subordinate dog or when an older, dominant dog can no longer maintain dominance. Further, owners can play a part in creating this conflict too. For instance, an owner may not support the dominant dog's position but try to treat both equally instead, they may give preferential treatment to the subordinate dog and interrupt or interfere with the dominant dog's ability to control certain items like toys, beds or attention, or they may stop or prevent dogs from expressing dominance-related signals and behavior.

It's important that you deal with canine rivalry. There is always the potential for the dogs or family members to be injured. Because this can be a difficult problem to combat on your own, it often helps to get the assistance of a professional animal behaviorist. They can help you utilize counterconditioning and desensitization techniques to bring about and reinforce nonaggressive behaviors.

There are several things that you can do on your own. First, you can support the dominant dog's position. If you're unclear about which dog is the dominant one, there are some signs that you can look for. Dominant dogs may stand over another dog, placing his neck or paws on the shoulders of the other dog. Also, if one of your dogs demands to be the first at everything – the first petted, the first to go outside, the first to be fed, the first at the toys – then that one is likely the dominant one. Keep in mind, however, that your dogs may be dominant in different situations, one with food, another with toys and so on. Once you've determined who is dominant, do not prevent that one from asserting his position. Also, it's important that all humans in the pack have established dominance over the dogs. If your dogs have not been spayed or neutered, doing so can make a big difference. Your dogs may also need to be checked by your veterinarian to rule out any health problems. It's also very important not to punish your dogs as this can actually worsen the situation.