Dogs fight for a number of different reasons, but quests for dominance often underlie much of the sparring. Aggressive incidents may be isolated to one or two specific situations, such as competition over specific resources or space guarding issues. Hierarchical disputes are more common among dogs of the same sex and fights between two females are typically more vicious. Any breed can develop such hierarchical disputes as this goes hand in hand with "pack" mentality, but it may be more difficult to maintain stable hierarchies with terrier breeds and other breeds that have been selected to work independently.
Dogs in the same household will fight if they are near equal in social status. This can occur in two distinct situations. Hierarchical disputes may arise if there is a change in dominance because the original top ranking dog loses status as he weakens with age or when a younger dog with a desire for a higher status reaches social maturity (18 months to 3 years of age) and begins to challenge the incumbent. Social relationships may also be affected when a new dog is introduced to the social group or when a dog is reunited with his social group following a period of absence. Under all of these circumstances, disputes are usually not life threatening and a new hierarchy will be established within a few weeks as long as the owners do not intervene.
Alliance aggression is more common. This occurs when the owner interferes with the establishment of a stable social hierarchy because he/she continually protects the submissive dog and punishes the top-ranking dog. Such misguided owner alliance effectively lowers the rank of the dominant dog and elevates the status of the submissive dog, which perpetuates and exacerbates the competition between the dogs.
Aggression due to owner alliance issues can be very dangerous and may persist for some time. The fights are often vicious and result in injury to one or both dogs. In alliance situations, the dogs generally fight only in the owner's presence, but can peacefully cohabitate in the owner's absence.
In most cases, both dogs are less respectful than they should be to the owner since the presence of a dominant individual within the social group tends to suppress aggression between other pack members.
Unfortunately, some dogs are socially dysfunctional and may never integrate well in a canine social group. In particular, dogs that have not received appropriate social contact with other dogs during their sensitive period of social development may never acclimate well to other dogs.
A complete physical examination is recommended to rule out any underlying medical condition that may be contributing to the dog's aggressive behavior. If the dog receives a clean bill of health, a behavior specialist can provide a diagnosis and an appropriate treatment plan.
Neutering may reduce aggression between dogs in the household since some aggression may be hormonally based.
The owner must establish a strong leadership role over all dogs in the household via a non-confrontational dominance program. Owner leadership is essential for safely establishing and maintaining a stable social hierarchy.
It is important to avoid further confrontations between the dogs to prevent reinforcement of the learned component of aggression. Owners need to identify all sources of conflict and competition and change their management strategy so that they can prevent future altercations between the dogs.
The owner must determine which dog is most likely to achieve and maintain a dominant status and reinforce his higher ranking position by ensuring that he is the first to receive access to all resources. The second ranking dog should be obliged to follow. This decision is based on the age, tenure, health, and temperament of the two dogs. In general, the elder, incumbent dog is the one to support ("senior support program") and this approach is usually the best one when setting out to correct such problems.
In the event that the dogs begin to compete over a resource, the subordinate dog should be removed from the situation while the top ranking dog remains in the company of the owners.
Verbal correction directed towards the subordinate may be effective at curbing aggression when the subordinate does not readily defer to the dominant dog's initiative.
If fighting is severe, the dogs may need to be separated and gradually reintroduced using systematic desensitization and counter-conditioning training methods.
In some instances, pharmacological therapy can facilitate the reintroduction of feuding dogs. Anxiety-reducing drugs or antidepressants are the medications of choice.
The usual background adjustments of providing appropriate daily aerobic exercise, an all-natural non-performance diet and regular daily obedience training sessions are highly recommended.
Training the dogs to wear a head halter or body harness with trailing leashes and a basket muzzle will increase the owner's level of control and safety when the dogs are together.
For safety reasons, it may become necessary to confine the dogs to crates or separate rooms. They should not be allowed to have visual contact when confined if they continue to threaten each other. This may increase their arousal levels thus perpetuating and possibly exacerbating their aggression towards one another.
Adopting a dog whose temperament is compatible with the personality of your other dog is of the utmost importance in terms of avoiding this problem. Some dogs (individuals and particular breeds) may be genetically predisposed to developing a dominant temperament so it is important that you research the breed as well as the breed lines before selecting a canine companion to join your canine pack. Establishing your role as the benevolent leader early on in your relationship with a new puppy is essential. Obedience training, early socialization, management styles that reduce conflict between the dogs, and proper introductions, all help promote positive social integration. It is often easier to introduce dogs of the opposite sex.