Aggression Between Family Dogs

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Aggression Between Family Dogs

Interdog Aggression Explained

In addition to actual fights, aggressive behavior can include mounting, blocking, standing over another dog, posturing, staring, and vocalization. Dogs in the same household can become aggressive toward each other for a variety of different reasons. Aggression may be dominance-related, territorial, possessive, or caused by fear/anxiety. Some dogs have “alliance aggression”. This occurs when dogs only show aggression in the presence of their owners and are peaceful when they are alone. These dogs typically fight over owner attention and many times have problems when they try to greet the owner simultaneously. If the dogs are intact, aggression may be hormone driven. This type of aggression is suspected if intact males are aggressive to other males, if females are aggressive during their heat cycles, or if a mother is protecting her pups. In these cases, spaying and neutering the dogs may help. Other common causes of aggression involve changes within the household that lead to an unstable hierarchy, such as the addition of a new dog, social maturity of a puppy (occurs around 3 years of age), declining health of an aging pet, or loss of a canine or human family member. Owners must be aware that dog social structure is not necessarily straightforward. A dog’s position within the hierarchy can be fluid and change over time or with different circumstances (e.g. one dog may get priority with toys, while another may be the top dog when it comes to food). This can make identifying the “alpha dog” tricky. Some dogs may be predisposed to aggression if they were not well socialized as puppies, have experienced social trauma (human or dog related), or lack good training. Studies have shown that up to 50% of aggressive dogs also suffer from separation anxiety, while 30% suffer from phobias or generalized anxiety. This supports the theory that many of these dogs use aggression to control situations that make them uncertain, anxious or fearful. Up to 20% of interdog aggressive dogs also show aggression toward owners, indicating that owner conflict is often also a problem. Owner behavior that may inadvertently contribute to aggression includes: interference with normal social rituals, reinforcement of aggressive behavior, frequently scolds/yells/gets upset (increases dog’s tension and arousal), owners that respond inconsistently to dog’s behavior, and lack of training/control of dogs. Aggression can be treated. First, the dogs should be examined to rule out physical problems that may contribute to aggression, such as hormone disorders or painful conditions (e.g. arthritis). The overall safety of the situation should also be evaluated. If severe bites have occurred to humans or dogs, aggression triggers are unpredictable, or the home situation is such that treatment would be difficult, then re-homing may be recommended.

Aggression Treatment

Treatment for aggression takes time and effort. It may take weeks to months before improvement is seen. With proper management, improvement is seen in 96% of cases, with median improvement in aggression rated at 69%. Treatment involves:

1) Avoiding aggressive situations and triggers

2) Starting a “nothing in life is free” program

3) Giving preference to one dog

4) Desensitization and counter-conditioning

5) Medication, such as fluoxetine, to reduce anxiety and aggression

Depending on the situation, one or all of these techniques may be recommended. Medication alone does not usually lead to successful resolution of the aggression. Some form of behavior modification (#1-4) is very important to success. Spaying and neutering of intact dogs may also help. Exercise can have a calming effect, so taking the dogs for walks or runs may be recommended. Punishment should be avoided as it may either escalate the aggression or redirect it toward the owner. Every human member of the household must be on the same page so that household routines and interactions with the dogs are consistent. Treatment protocols that are inconsistently used over time or between household members sends mixed messages to dogs, resulting in ambiguity and treatment failure.

Avoiding Triggers

First you want to avoid situations that may trigger aggression. Common triggers include competition for resources. Resources may include food, treats, toys, preferred resting places, owner proximity or owner attention. In theses instances, dogs should only be fed, given treats, played with, and allowed to greet owners separately. Deny both dogs free access to food, toys, treats, or preferred resting places. Other common triggers include situations that induce excitement, such as when greeting people, play sessions, walks, car rides, running the property line, barking at passerby, etc. Separating the dogs or intervening before the dogs become too excited may help in these situations. In some cases, dogs must be completely separated then gradually reintroduced with desensitization and counter-conditioning training. If the dogs are separated, make sure they cannot see and aggressively posture at each other through gates, doors or windows.

Nothing in Life is Free

This program helps to create better communication and consistent interactions between the dogs and owner. Basically, the dogs have to earn everything they get, including food, treats, toys, petting and owner attention. They do this by calmly following owner commands. These commands can involve a simple come-sit-stay to a full obedience session. If the dogs have not previously received obedience training, work on the come, sit and stay commands first. Each dog only receives the resource (food, attention, treats, etc) after he has obeyed the command. Ignore attention seeking or pushy behavior. Every interaction should be initiated and stopped by the owner, not the dog. Work with each dog individually first, then together once it is safe to do so. By learning to sit or lay down in the presence of a resource, dogs learn to remain calm in a situation that may have previously triggered a fight. If fights are caused by alliance aggression, independence training may be helpful.

Showing Preference

Another helpful approach is to select one dog to consistently receive first access to resources such as food, treats, favorite resting places, toys, having the leash put on first, access to door ways, and attention. This dog should also receive the best resources (preferred place on the couch, favorite toy, etc). Initially, you may choose the older dog or the dog that was acquired first to receive preference. If no improvement is seen after 6 weeks, try switching preference to the other dog. Giving one dog priority access to resources reduces conflict because it reduces unpredictability and provides structure. When used in combination with the Nothing in Life is Free program, dogs learn the order in which each will receive a resource, and the dog that receives the resource second must wait until the first dog has the opportunity to earn the resource.

Densensitization & Counter-Conditioning

This program involves gradually exposing the dogs to each other in such a way that they learn positive experiences occur when the other dog is near. The dogs should be under absolute control with leashes, head halters, and/or basket muzzles as necessary. Each handler and dog should be far enough away from the other handler and dog that neither dog shows any signs of aggression. The pets are then asked to obey obedience commands and rewarded with treats, play or attention. The tone of the handlers should be happy and upbeat. Avoid sounding angry or frustrated and avoid any punishments. For each consecutive session, gradually decrease the distance between dogs during obedience training. If aggressive behavior is seen, increase the distance and proceed with distance reduction more slowly. Sessions should be short and frequent. If the dogs are not aggressive on leash or during walks (most are not unless aggression is severe), walking the dogs together is a good way to help the pets bond and release some energy. Use head halters and start with the handlers walking between the dogs, then progress to the dogs walking side by side. Dogs should be taught to sit and stay at a safe distance apart when stopping to cross streets.


Your veterinarian should determine whether medication is appropriate for your pet to help treat aggression. If the dog is aggressive because of pain, pain medication may be indicated. The most common medication prescribed for aggression is fluoxetin. Fluoxetin is an SSRI (selective serotonin reuptake inhibitor). It can take up to 2-4 weeks before results are seen. Adjustments in dosage may also be recommended by your veterinarian to achieve desired results. In addition to reducing aggression, fluoxetine also helps treat anxiety. Side effects of fluoxetine are uncommon and include sedation, vomiting, decreased appetite, constipation, agitation, and seizures. Fluoxetine should be used cautiously with Tramadol or in patients with a history of seizures. It should not be used concurrently with MOI medications.

Other tips

Some dogs may benefit from anti-anxiety products such as Adaptil (spray, collar, diffuser) or Thundershirts. Obedience training, regular exercise and spaying/neutering are also helpful.


In addition to avoiding triggers, head collars (e.g. Gentle Leader) with a trailing leash may be worn by both dogs. If aggressive behavior or fighting occurs, the trailing leashes can be grabbed easily and used to separate the dogs. Aversive citronella spray (e.g. Spray Shield) can be used during dog fights to startle the dogs apart without harming them. Basket muzzles can be considered, but all dogs in the household must wear them. Dogs can eat, drink and pant with basket muzzles. Traditional muzzles that close the mouth should not be used in this situation. If fighting is severe, dogs should be completely separated until conditioning and other treatment protocols can be put in place. Re-homing should be considered if the aggression poses a significant safety issue. Please ask your veterinarian for more information.


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