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Aggression itself is usually defined by canine behaviorists as "the intent to do harm". Many dogs show "displays of aggression" such as barking, growling, or snapping in the air, which are considered distance-increasing actions, those that intend to get the person or dog to move away from the dog. Some dog-aggressive dogs display aggression that is mainly defensive, and they harm another dog only if they perceive that they have no option. Yet, other dogs may develop dog-aggressive behaviour due to medical reasons, such as hormonal imbalances.
Dog aggression is a common dog behavior, and can be seen in all breeds of dogs. The breed standard usually spells out whether dog aggression is common in the breed and to what degree it is allowed. Most of the terrier breeds and the bull breeds are believed to have a higher likelihood of developing dog-aggression upon reaching maturity. Individual dogs may or may not display the level of aggression that their breed standard suggests.
As well as breeding, a dog's experiences may affect his chance of developing dog aggression. A dog that is attacked as a puppy may develop fear-based dog aggression towards all dogs, or perhaps only towards dogs that resemble the dog that attacked him. Although people tend to bring these reactions out of dogs more often than dogs themselves, dogs only pay attention to what their owners allow.
Dogs that display dog-aggressive behaviour do not necessarily show aggressive behaviour towards humans. The two types of aggression are not necessarily related, and do not always occur in the same animal.
Factors contributing to aggression
- Anxiety, fear or phobia
- Lack of structure
- Lack of proper exposure to other dogs during the critical socialization period
- Early imprinting by an aggressive or nervous dam
- A traumatic experience
- Territorial behavior
- Thyroid malfunction or other medical conditions
- Abuse from owners
- Medical or physical ailments
- Breeding and genetic predisposition
- Taken from mother too soon
- Lack of clear direction from owner
Dog aggression manifests at the age of adolescence to social maturity (6 months to 4 years). Warning signs such as fear and/or nervousness around other dogs, displays of aggression only under certain circumstances (while on leash, in the presence of food, in the presence of the owner, etc.), or most commonly, over-the-top play behavior can be seen at any stage of the dog's development. Play behavior such as tackling, chasing, mouthing, nipping, pawing, and wrestling are all normal canine behaviors that serve the evolutionary function of preparing the young dog for later combat and hunting. Young dogs that engage in excessive amounts of these behaviors are much more likely to develop dog aggression as they age.
Dog-dog aggression should not be confused with dog-human aggression (in the past, this was referred to as "dominance" aggression when directed at the owner, but is now simply called owner-directed aggression).
Many people commonly mistake fear and anxiety-related aggression as "dominance aggression," which is inaccurate. Dominance is rarely the cause of aggressive behaviors in dogs, with fear and anxiety being the greatest cause of both dog- and human-directed aggression.
Lack of exercise is not a cause of aggressive behavior, although exercise boosts serotonin levels, which offsets stress hormones such as cortisol, and can complement a behavior modification program. However, it is a common misbelief that aggressive dogs are "not exercised enough." Many aggressive dogs are exercised regularly.
Fading dog aggression
The form that treatment for dog aggression takes depends on the underlying cause of the aggression, and an accurate assessment is therefore essential. Most reputable trainers recommend that a dog has a vet screen for medical changes that may cause aggression before attempting any form of behavioural modification.
Dogs that are aggressive from fear can be that way either from genetic predisposition ("weak nerves"), or from a traumatic experience. With these dogs, a programme of gradual desensitisation (DS) and counter-conditioning (CC) is often used to reduce the dog's reactivity to the stimulus that triggers the aggression. This can be accomplished through management (minimizing the dog's exposure to situations where he can practice the behavior while working on the training program) food rewards, toy/play rewards and praise as a reward. Ignoring aggressive behaviors is not standard or sound advice when implementing a DS/CC program.
Behavior Adjustment Training (BAT) is a newly publicized treatment option that uses functional analysis and systematic desensitization. With BAT, the dog's original function of increasing (or decreasing) distance is used as a reinforcement for alternate behavior (head turns, ground sniffing, body turns, etc.). This is done by creating set-up situations in which the dog is able to offer alternate behavior, and allowing/encouraging the dog to walk away. With repetition, the dog learns to turn her head, sniff the ground, etc. as a way to increase distance without aggression, and gradually becomes comfortable with the former trigger.
Punishing aggressive behaviors through the use of leash "corrections" or leash "pops" and/or the use of training collars such as choke, prong or shock, is not recommended in cases of fear-based aggression, as these measures run a high risk of increasing the dog's anxiety in those situations. Further, it is difficult to control what the dog associates the punishment to, as it is often what the dog is looking at the moment it is corrected, so sloppy application of punishment can create a more negative association to the stimulus than before. The final risk with punishment in treating aggression is that it runs the risk of punishing the aggressive display, such as growling, barking, baring teeth, etc., which are all warnings. Punishment decreases behavior, but does not modify it, so the dog may stop exhibiting aggressive displays (designed to increase distance between the dog and the stimulus) and skip straight to aggressive actions, such as biting.
"Dominance" based approaches are highly controversial and more formal study is needed to validate these methods. Further, these approaches carry a greater risk of behavioral fallout, such as the escalation of the aggressive behavior and/or redirected aggression on the owner or other family members.