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Behaviour & Training


Every dog, and every breed of dog, is capable of showing aggression. It's just that some are more likely to show it than others, in many different ways:

  • Growling
  • Snarling
  • Baring teeth
  • Lifting the lip
  • Raising of the fur along their back (‘raised hackles')
  • Wagging the tail stiffly
  • Barking
  • Lunging
  • Snapping
  • Biting

While most of these are obvious in their intent, others can be quite unclear and contradictory, especially wagging the tail stiffly.

If you're looking for answers about your dog's aggression levels, take into account all observable behaviour signs to help identify the type of aggression your dog has, as well as the possible underlying causes.

What Are The Different Types Of Aggression?

It usually depends on the situation the dog is in, and who else is present.

Resource-guarding Or Possessive Aggression

Dogs show this type of aggression when they have something they don't want to share, but then are approached by a person or another dog. It might be a bowl of food, a bone or even their favourite bed.

Fear Aggression

This is an attempt by a dog to increase their personal space and to try and stop a fearful thing from getting closer to and affecting them – be it a stranger, another dog or even a visit to the veterinarian.

Inter-dog Aggression

This is aggression directed at other dogs, both known or unfamiliar.

Irritable Aggression

Shown by dogs when they're in pain or unwell. Most commonly displayed by older dogs (and grumpy old men...).

Territorial/Protective Aggression

Dogs being aggressive from behind a fence are a classic example of this type of aggression. They're being protective of their patch. Some dogs even do this when walking on a leash – they're being protective of their owner.

Play Aggression

We've all seen this at the local off-leash park – two dogs playing like they're ripping each other's heads off! Usually, they keep themselves in check without it escalating.

Other Causes

Sometimes we don't even know why it is occurring.


Aren't Only Certain Breeds Of Dog Aggressive?

No, any breed can be aggressive. And given the right (or wrong) circumstances, every dog has it in them to bite.

What Causes A Dog To Be Aggressive?

As with people, there can be a lot of different catalysts behind a dog's aggressive behaviour. Correct diagnosis is the starting point to management, treatment and re-training.

Poor Social Skills

The critical socialization period for every dog occurs at an early age – from 3 weeks to 4 months of age. This is when a dog needs to have lots of enjoyable, varied experiences with lots of different dogs and people. A puppy that misses out on these formative experiences can become aggressive when they're older. But the learning doesn't end there. As a dog gets older, it still needs regular, fun exposure to different people and dogs so it continues to develop and refine its social skills.

Bad Past Experiences

A negative experience in a dog's past can make them aggressive in that situation in the future. For example, if a pup was attacked by a small white dog, it might grow up to become aggressive to all white dogs.


Sometimes a single bad experience can snowball to become applied to many different future situations. For instance, using the same example above, the pup attacked by the small white dog may grow up to project this experience onto all small white dogs, and then to all white dogs, and then to all dogs, and so on.

Individual Temperament

Some dogs have a genetic basis to their aggression. Their mum or dad may have been aggressive and passed this trait on. This may not become evident until the dog is older.

Social Maturity

Some dogs start showing aggression at around 18-36 months of age. This indicates a gap in their social maturity.

The Current Situation

How a dog feels about being in a certain situation can determine whether they react to it aggressively. For example, not all dogs show aggression at the veterinary clinic, but some dogs do. Most vets understand that this is a ‘normal' occurrence as the unfamiliar sights, smells and sounds can unnerve many otherwise well-behaved dogs.

My Dog Is Showing Aggression. What Should I Do?

Aggression is a serious problem. If an incorrect diagnosis of the cause of aggression is made, the wrong management approach is likely to be implemented, which could make the aggression worse.

Additional Information

The Merck Veterinary Manual

Veterinary Partner: The Canine Behaviour Series
By: Kathy Diamond Davis, Trainer

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