If your younger dog always deferred to the older dog, but now they fight, one scenario may be that an older, previously dominant dog is challenged by a younger, more domineering dog. This may happen as the older dog ages, or as the younger dog reaches behavioral maturity at 12 to 36 months. This may be an attempt to alter the existing hierarchy but at other times the dog is being a “bully.” Sometimes the older dog will acquiesce and things are fine, but at other times the owners do not want the change and intervene. In some situations, the older dog will not relinquish the dominant role even though it cannot physically compete with the younger dog. This can result in severe, injurious fights.
Breaking up a fight can be a dangerous situation for people and dogs alike. Owners usually try to reach for the collar of the fighting dogs, or if one is small, pick it up. This can result in severe owner injury if the fighting is very intense. If both are wearing leashes, they can usually be pulled apart. If all else fails, you might be able to break up the fight with a water rifle, citronella spray, broom or another distraction (such as pepper spray or a fire extinguisher). Reaching for the dog is usually the worst thing to do, as you could be injured (either accidentally or intentionally).
When people intervene in dogfights, redirected aggression is possible. Aggression (growl, snarl or bite) can be redirected to a person, animal or object other than that which evoked the aggression. If during the course of a dogfight, you pick up one of the dogs, the other may continue to attack and direct it at you.
Aggression between household dogs can be difficult to treat. You will need to identify the subordinate dog and ensure that you are not encouraging the subordinate dog to challenge the more dominant. It is critical that you never come to the aid of the subordinate against the more dominant. If left alone, the dogs will often use posturing and threats to end encounters without injury. If one dog backs down, the problem may be resolved. However, when neither dog is willing to give up the dominant position (as in a young dog challenging an older dog in the home), fighting will usually result.
A common owner error is the desire to make life “fair.” This often results in owners allowing subordinate dogs access to resources, such as attention, treats, toys, or entry into territory that they would not normally have. Usually the subordinate dog would not behave in a manner that would challenge the dominant when no one is around to “protect” it. If you encourage or protect the subordinate dog, it may be “tempted” to break the “rules,” and the dominant dog may become aggressive to enforce the “rules.” If you then punish the dominant dog for aggression, the subordinate dog learns it can engage in prohibited behavior while the owner is present. This is why, in many households, there is no fighting when the owners are gone. The subordinate is aware of the hierarchy and does nothing to challenge the dominant dog, unless the owners are around to intervene.
Another potential problem may occur when the relationship between individuals is context dependent. In other words, one dog may be dominant about owner attention but may not care who eats first. This is why it is important to understand the entire social relationship between dogs.
Although the dominance relationship between the two dogs must be dealt with, the first step is for the owner to gain complete control over both dogs. As leader or alpha, your presence and commands should be sufficient to prevent all dominance challenges between dogs and to intervene as needed when threats emerge. Control of each dog is achieved through the use of verbal commands, by leaving a leash and head halter attached for immediate control and by withholding all rewards unless earned. Attention on demand not only encourages situations where one dog may challenge the other, but also allows your dogs to control you. Inattention on demand teaches the dogs that all rewards are provided only when you choose, and reduces or eliminates those situations where challenges might occur. Head halter with leash control and obedience-reward based training of each dog should first be done separately. With a head halter and remote leash on each dog you will have effective control, and a means of controlling and separating the dogs if needed. With control of the head and mouth, aggressive threats can be curtailed and either dog can be placed in a subordinate posture, by pulling up on the leash, closing the mouth, looking the dog in the eyes, or pulling the head sideways so that the dog’s gaze is averted. In severe cases muzzles may be needed to keep people and dogs safe while therapy is undertaken.
Next, treatment must be designed to identify and support the dominant dog. Several differing treatment plans exist. One is supporting the dog that has been in the household the longest; usually this is the oldest dog. Another treatment is to identify the dominant dog based on how the dogs interact, in other words, who threatens and who defers. Care must be exercised to watch for bullies who do not allow other dogs any status and are not consistent in the application of threats and response to deference. All dogs must have some status and the ability to respond in an appropriate manner and thus avoid aggression.
In some cases the dog that is chosen is the younger, larger, more physically capable dog, if this dog wishes to be the leader. Often, this is also the aggressor. You must allow the dominant dog priority to go outside, to come in, or to receive food or owner attention and affection. If you are petting the dominant dog and the subordinate dog approaches, make it wait. Importantly, you must avoid all circumstances that elicit aggression. If the more dominant dog approaches or challenges the subordinate dog and the subordinate dog assumes a subordinate posture, the owners are not to intervene as long as the dominant dogs stop. If the dogs are likely to fight when you are away or at homecomings, separate the dogs whenever you are out or are not available to supervise.