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Interdog Aggression in Dogs

Inter-dog aggression occurs when a dog is overly aggressive towards dogs in the same household or unfamiliar dogs. This behavior is often considered normal, but some dogs can become excessively aggressive due to learning and genetic factors.

Inter-dog aggression occurs much more frequently in non-neutered male dogs. Common signs usually start appearing when the dog reaches puberty (between six and nine months old) or becomes socially mature at 18 to 36 months. Generally, inter-dog aggression is more of a problem between dogs of the same gender.

Symptoms and Types

The most common symptoms of inter-dog aggression include growling, biting, lip lifting, snapping, and lunging towards another dog. These behaviors may be accompanied by fearful or submissive body postures and expressions such as crouching, tucking the tail under, licking the lips, and backing away. Typically, before a severe inter-dog aggression incident in the same household occurs, more discreet signs of social control will become noticeable. One tactic a dog may use is staring and blocking the other dog’s entrance into a room. A specific condition sometimes triggers the aggression, even though the dogs normally get along well.

Causes

The causes of this condition vary. A dog may have become overly aggressive because of its past experiences. For example, it may not have socialized with other dogs as a puppy, or it may have had a traumatic encounter with another dog. An owner's behavior may also influence a manifestation of the condition (e.g., if an owner shows compassion for a weaker dog by punishing the more dominant dog). Other reasons for aggression are fear, wanting to protect territory and social status, or a painful medical condition.

Selective breeding and genetics are also a factor. Dogs bred for fighting, such as pit bull terriers, tend to exhibit inter-dog aggression more frequently.

Diagnosis

There is no official procedure to diagnose inter-dog aggression. Some symptoms are very similar to canine “play” behavior and excited, non-aggressive arousal. Biochemistry, urine analysis, and other laboratory tests usually yield unremarkable results. But if any abnormalities are identified, they may help the veterinarian find an underlying cause for the aggression. 

If a neurological condition is suspected, an MRI scan may be necessary to determine whether it is a central nervous system (CNS) disease, or to rule out other underlying neurological conditions.