Aggression between dogs can result in injury to dogs and/or to the people trying to separate them. The behavior can consist of growling, snarling, barking, lunging, snapping and biting. Aggression between unfamiliar dogs can be due to dominance, fear, or protective behavior over territory or owner. There are several reasons why dogs show aggression:
Dominance Motivated Aggression
This aggression can be elicited by dominant gestures or postures from either dog which can include placing the head or feet on the back of the other dog, dominant body postures such as eye contact, and high tail and stiff legged approach. Owners may inadvertently reinforce the behavior by leash tightening and giving vocal cues which signals to their dog that the impending approach is problematic.
Dogs of near equal dominance and those of the same sex are most likely to compete for dominance. Some extremely bold or assertive dogs will fight rather than back down when challenged. Although dominance challenges may be a source of aggression when two dogs are meeting each other for the first time, most dominance hierarchies are established with posturing and no fights. It is likely therefore that fear, territorial behavior and learned components would contribute to an attack. Dominant aggressive dogs may be over-assertive and/or overprotective if the owners do not have good control or have taken a subordinate position in relationship to the dog.
Territorial Aggression Towards Other Dogs
This aggression is primarily exhibited when unfamiliar dogs are on the resident dog’s property, or what the aggressor considers his territory. Some dogs get highly aroused at the sight of other dogs on their territory and may jump fences, or go through windows or doors to get to the intruder.
Fear-Based Aggression Towards Unfamiliar Dogs
This aggression is very common in aggressive encounters with other dogs. The diagnosis is made based on the body postures and reaction of the dog when faced with another dog. The fearful dog will often have the tail tucked, ears back and may lean against the owner or attempt to get behind them. They may be barking at the approaching dog and backing up at the same time. Often the dog avoids eye contact. Owners that try and calm their aggressive dog may serve to reinforce the aggression, while those that try and punish the dog will only serve to heighten the dog’s fear and anxiety in relationship to the stimulus. Good control can help to calm the dog, while owners who have their dogs restrained on a leash (especially with a choke or pinch collar) and have poor control often have highly defensive dogs. Dogs that are restrained on a leash or tied up are more likely to display aggression when frightened, because they cannot escape.
Learned Threats or Aggression
Should threats or aggression result in the retreat (or removal by the owner) of the other dog, the behavior has been successful. If the owner tries to calm the aggressive dog or distract it with food treats, this may only serve to reward the aggressive behavior. One of the most common mistakes is to punish the dog that is aggressive toward other dogs. This usually serves to heighten the dog’s arousal, and teaches the dog that the stimulus (other dog) is indeed associated with unpleasant consequences. Many owners, in an attempt to gain more control, then increase the level or type of punishment (e.g. prong collars) which further heighten the dog’s fear and in some cases may lead to retaliation and defensive aggression toward the owners.
Prevention starts with puppy training and socialization. Early and frequent association with other dogs will enable your pet to learn proper interactions and reactions to other dogs. This can be very helpful in prevention of aggression to other dogs.
You must also have good control of your dog who should reliably respond to commands to ‘sit’, ‘stay’ and ‘quiet’. If necessary, the dog may need a head halter to give you additional control.
How to Deal with an Already-Aggressive Dog
First and foremost, you must have complete control over your pet. This not only serves to calm the dog and reduce its anxiety, but also allows you to successfully deal with each encounter with other dogs. Leashes are essential and the use of head collars and/or muzzles are strongly recommended for dogs that will be in situations with multiple dogs.
Begin by establishing reliable responses to basic obedience commands. If the dog cannot be taught to ‘sit’, ‘stay’, ‘come’ and ‘heel’, in the absence of potential problems, then there is no chance that the dog will respond obediently in problematic situations. Reward selection can be critical in these cases, since the dog needs to be taught that obedient behavior in the presence of the stimulus (other dog) can earn the dog-favored rewards. The goal is that the dog learns to associate the approach of other dogs with rewards.
Long-term treatment consists of desensitization (gradual exposure) and counter-conditioning the dog so that the approach of the other dogs leads to a positive emotional response. In training terms the dog must be taught to display an appropriate, acceptable response when other dogs approach (e.g. ‘sit’, ‘watch’, ‘relax’) which can be reinforced (differential reinforcement or response substitution). This must be done slowly, beginning with situations where the dog can be successfully controlled and rewarded and very slowly progressing to more difficult encounters and environments.
Lastly, for fear-aggressive dogs in particular, anti-anxiety drugs may help to calm the dog enough so that the retraining session is successful. For situations where the problem has become highly conditioned and intense, antidepressants may be useful for regaining control. In most cases however, the best calming influence is a head halter, good owner control and some strong rewards.