Do dogs bite for no reason?

Aggression is one of the most common behavioural problems in dogs. Aggression is often easy to diagnose but difficult to manage, because it is often multifactorial. There are several different categories of aggression. Let's look at the different types of aggression in dogs.

Aggression in dogs

Aggression can be classified into several different categories. Fighting amongst dogs in the same household is probably the most common aggression problem, followed by aggression to unfamiliar people. It is not always possible to prevent aggression but it can usually be controlled with effective management. In some cases, re-homing an aggressive animal may be a suitable solution and in a few cases, euthanasia may be the only option.

Aggression can be classified as target based or motivation based.

Target based aggression includes:

  • Aggression towards people - familiar or unfamiliar
  • Aggression towards other dogs - familiar or unfamiliar

Motivation based aggression includes:

  • Fear related (defensive) aggression
  • Pain related aggression
  • Territorial aggression
  • Status related aggression
  • Possessive aggression (over resources such as food or toys)
  • Competitive (inter dog) aggression
  • Redirected aggression
  • Play aggression
  • Maternal aggression
  • Predatory aggression
  • Learnt aggression

In most cases, more than one type of aggression is demonstrated and learnt aggression can follow from any type of aggression. In general the most common cause of aggression towards familial people or dogs is status related, while aggression directed towards unfamiliar people or humans is most commonly territorial or fear related aggression.

Fear related aggression

This is the most common form of aggression in dogs. It is often triggered by something that the dog interprets as threatening and it initiates the flight or fight response. Early traumatic experiences or lack of appropriate social interaction often contributes to this type of aggression. Genetic factors, maturity, learning, the initiating stimulus and ability to escape may all play a role in the dog’s response. Fearful dogs may try to avoid a fearful stimulus (flight) but become aggressive (fight) if they cannot flee (for example when they are leashed, confined, cornered or physically restrained). Fear related aggression may also be triggered when a dog is forced to remain in one area without the option of escape (for example on the property or between the owner and the stimulus, or near a resource such as food). Aggression could also be encouraged by offering a reward after removing a threat in an aggressive manner. Inadequate socialisation, reinforcement of aggressive behaviour, and aggressive punishment for undesirable behaviour can all lead to fear related aggression.

Pain related aggression

Pain related aggression is often associated with chronic, low-grade pain that increases irritability and defensiveness. An old, arthritic dog could for instance fall into this category. Treating the problem may resolve the issue but the learnt behavior may persist. An acutely painful incident will be remembered and may also trigger this behavior. If a dog had, for instance, a painful injection in the past, just seeing a syringe on another occasion may lead to fear or aggression.

Territorial aggression

Territorial aggression can be stationary (house or yard) or mobile (car). It is most often severe around entrances to territory with fences, doors and gates being the most common spot. It is usually most intense at the periphery of the entrance but the dog will be fine and probably friendly once the person or other animal has entered the property. Territorial aggression is often inadvertently reinforced as the target appears to retreat in response to the aggression when passing the territory. The behavior is often exacerbated when the dog is restrained.

Status related aggression

Status related aggression may be referred to as irritable, conflict or impulse control aggression, and was previously referred to as dominance aggression.  It is directed towards family members (both other dogs and people) and familiar people. It is generally associated with preferred resources such as food, toys and sleeping areas (resource guarding). Interactions such as petting, handling, moving or reprimanding the dog may elicit a response. Some reactions may be impulsive, unpredictable and intense.

When a dog successfully uses aggression to achieve a goal or remove a threat, the dog learns that aggression is successful (negative reinforcement). This behavior is most commonly seen around social maturity (one to three years of age) and is mostly associated with anxiety, poor communication and lack of consistency and structure. Treatment includes providing clear leadership with consistency and structure in the interactions with the dog. Avoiding potential problem situations is the first step. Dogs should learn to sit for food and treats. The person should initiate attention and owners should not respond to attention seeking behavior from the dogs. In some cases, dogs may need medication to alleviate anxiety. 

Possessive aggression

Possessive aggression occurs when aggression is directed towards a person or dog over resources such as food, toys and beds. It is often quite normal but can become more serious if the aggression is learnt. Food has an intrinsic value so if a dog growls when it is approached during a meal and the bowl is removed, the aggression is founded and exacerbated. A puppy may learn that certain objects such as toys attract attention (extrinsic behavior), particularly if it is forcibly removed. Forcibly removing the item and punishing the puppy may instill fear. As the puppy matures, the anticipation of punishment may turn into aggression as an owner tries to retrieve the object. This problem can be avoided if puppies are taught to give up items from an early age by rewarding relinquishment. Food aggression is treated by desensitising the dog to approaches from people while it is eating.

Competitive (inter dog) aggression

Competitive aggression between dogs within the same household is usually manifested when one or both dogs reach social maturity between one and three years of age. The dogs will have been fine with each other up to this stage and suddenly start fighting. Inter dog aggression is most commonly seen between dogs of the same gender and size but can occur between any two animals. Fights are often triggered over access to resources such as food or sleeping places or may occur over excitement of their owner arriving home. Some dogs are inappropriately aggressive where the level of aggression is not in line with the level of the threat, for instance the dog continues to attack even when the other dog backs down. Inter dog aggression may be appropriate and it is important that owners establish effective leadership through good resource management and reinforcing the natural inter dog hierarchy. Inter dog hierarchy may not always be very clear and may be dynamic. Different dogs may be top dog in different situations with different resources. The most important aspect of inter dog aggression is that dogs realise and recognise the leadership of the people in the household.

Redirected aggression

Redirected aggression occurs when a dog is aggressive towards a target that it cannot access (for example a dog or person on the other side of the fence), and the aggression is then redirected towards another target, usually the dog next to it. The most practical management of this behavior is removing the dog from the arousing stimulus by calling the dog away from the fence.

Maternal aggression

Maternal aggression occurs when a bitch with a litter of puppies attacks another dog or person approaching or interfering with the puppies. It may also be seen in bitches that are pseudo-pregnant and nesting. It usually subsides as the litter matures or as the influence of hormones decreases. It is controlled by spaying the bitch.

Predatory aggression

Predatory aggression is highly instinctive and directed at prey or something resembling prey (small cat or dog or squealing child). It is difficult to modify this behavior and the best solution is to keep the dog away from any potential victim. In some cases, re-homing the dog may be the best option.

Learnt aggression

Learnt aggression is often a complicating factor in dealing with a dog. A dog learns a behaviour by repeating things that have a desired effect. A dog that has learnt that bearing teeth has a desired effect, for example to gain food or a toy may not always show the warning signs before biting. It is an acquired behaviour and is often seen as an unprovoked, sudden attack. Learnt aggression is often not directed towards other dogs, as dogs are far more aware of the subtle warning signs before an attack. It is important to try and work out when the dog started being aggressive as this gives important clues as to how the aggression has progressed. On the surface it appears that the dog had no reason to attack so it is important to work out when the biting first started.

Management of aggression in dogs

It is important that medical conditions causing aggression be eliminated first.  Painful conditions, hormone imbalances and metabolic issues can be the sole reason for aggression but may also be part of a bigger problem. For example, arthritic dogs can be treated with anti-inflammatories and joint supplements to alleviate the pain.

It has been shown that the sex hormones, testosterone and oestrogen are key factors in aggression in dogs and cats. Testosterone is a powerful modulator of aggression in males and oestrogen has been found to increase aggression in females. Sterilisation may help reduce the incidence of aggression. It has been shown that inter-dog aggression responds favourably to sterilisation. It is usually advised to sterilise the less dominant, or losing dog, first. If fighting persists, the other dog should then be sterilised. Sterilisation appears to decrease the intensity of fights, while increasing the aggression threshold, which means it takes more for dogs to fight. Castrating males also tends to decrease roaming behaviour and urine marking, which are also undesirable behaviours.

Behavioural modification is an important tool in managing aggression. There are a few important tips to remember. Aggressive dogs should not be punished as this may worsen the aggressive behaviour. Positive reinforcement is helpful in training and inducing relaxation behaviour. Restraint techniques such as “wait” and “stay” as well as commands such as “sit”, “down” and “leave” are important in managing the dog. Consistency remains an important factor in training. It is important that all members of the household are on board and use the same techniques and commands when dealing with the dog. Desensitisation is important in the long term management of most types of aggression. This means dogs are exposed to a certain trigger for short periods until they become used to it.

What do you do when faced with a dog fight?

Preventing a dog fight before it happens is the best measure to follow. Watch for the subtle signs between two dogs. This may include a high tail posture, raised hackles (the hair along the back stands on end), circling and snarling. The best thing you can do when you see a dog fight looming is to get up and leave, keeping quiet while you do so. Shouting may cause one dog to launch an attack. If a dog fight is in the process, the best thing you can do is keep quiet and walk away. If you need to separate the dogs, use a broomstick to force in between the dogs’ jaws and throw a blanket over them or pour water over them to prevent them from getting oxygen. If the jaw grip has been released, pick up the smaller of the dogs immediately or grab it by its back legs and pull it away from the other dog as fast as you can and move it to another room so you can close a door in-between the dogs to separate them.  Sticking hands into the action zone will probably result in injury to you so be extremely careful. Once the dogs are separated, keep them away from each other until they are both calm. Do not punish either dog involved.

Aggression is the most common behavioural problem in dogs but it can be very difficult to manage. An aggressive personality cannot be completely altered so management of the aggressive behaviour may require a lifelong commitment from the owner. If the environment cannot be suitably managed, re-homing the animal may be the best option. In some cases, due to the dog being a danger to other dogs and people, euthanasia may be the best and kindest option. There is unfortunately no quick fix to any behavioural problem and it requires effort and consistency from everyone involved. Dealing with aggressive dogs can also be dangerous so it is important to seek professional assistance and advice.