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Why Is My Dog Suddenly Aggressive To Our Other Dog?

Understanding acts of aggression between two dogs who previously got along well requires us to identify a trigger point that lead to a sudden change in behaviour.

The most common reason why a dog is suddenly aggressive toward another dog from the same household is a dispute over one of three things:

  • Possessions
  • Food
  • Space / Territory

All three can be managed provided the problem is addressed promptly.

Aggression between two dogs from the same home is unpleasant and often shocking if it appears to come from nowhere. A dog being suddenly aggressive toward a dog who they are normally friends with can be jarring.

Key questions we need to establish the answers to when establishing the cause of sudden aggression between two dogs are:

  • Was this a one off incident?
  • Did you witness the event that lead up to the aggression?
  • How did the aggression manifest (i.e. snarling, lip curling, low growling or a full on bite)?
  • Did the aggression persist?
  • What was the other dog’s response to the aggression?
  • Has it happened more repeatedly since and what were the triggers?

Intact male dogs tend toward having more innate aggressive than either female dogs or neutered males. However, this is certainly no guarantee.

Aggression – including sudden aggression – can come from old dogs, young dogs, female to male and male to female.

Dogs are pack animals and the dynamic of the pack is established between dogs over a period of time.

I once had a client who came to me and asked this very question “why is my dog suddenly aggressive to our other dog?” when there had been absolutely no disruption to their previously harmonious relationship.

Upon further investigation the answer revealed itself. The aggressive dog, in this case a female, was spayed. The victim of her aggression – a young, intact male dog.

Another female dog in a yard nearby had come in to heat and the intact male dog had started showing sexual behaviour toward the female in his own household. The owner, unaware that this had happened, only caught the act of aggression but not the preceding behaviour.

The answer as to why this dog had suddenly become aggressive toward the other dog was discovered when we set up a secret camera.

As the amorous male started to bother his female housemate, she lashed out at him. This prompted further defensive aggression every time he came near her for a short time afterwards.

The problem eventually corrected itself with time, as if often the case, dogs can deal with other dogs quite well. Particularly dogs they know and have lived with for a long time.

So to summarise, if you have a dog that is suddenly aggressive to another dog in your own home you need to establish the exact trigger point. Look for the following:

  • Aggression related to food or toys
  • Aggression related to jealousy (one dog wants more attention from you)
  • Aggression related to fear
  • Aggression related to space / territory (as in the example provided above)

If aggression persists and you are unable to identify the trigger yourself, you should certainly seek the assistance of an experienced dog behaviour expert. Injuries between two dogs in the same home are more expensive and upsetting to deal with that fixing the problem before it gets that far.

Bonus tip: Is your dog’s diet responsible for aggressive behaviour? Click here.


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