Two aggressive dogs
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Why can dogs be aggressive with other dogs?

By Nick Whittle Author

Updated on the

Sometimes dogs just don't get on. This can be the case between unknown dogs or even between dogs of the same household, who may get bored of each other or step over an invisible line in the sand when it comes to food or their owner's cuddles.

Dog-on-dog aggression is a common occurrence but also one that causes upset and anxiety for owners. Households with more than one dog might experience some kind of rivalry and this will manifest itself in anything from short squabbles to sudden and violent brawls. In most cases, these moments of aggression are few and far between, but sometimes they can get out of hand.

This is more likely to happen with entire male dogs that have reached or passed 'puberty'. Most dogs will reach their equivalent of human puberty between six and nine months of age. However, all dogs may be aggressive, as it is normal form of communication for them.

How to spot aggression in dogs

Dogs will always give warning signs that they are uncomfortable before they lash out aggressively. It is important to pay attention to your dog's body language so you can notice some of the signs that your dog is going to react aggressively towards other dogs. Here are some of the tell-tale signs that your dog is about to behave aggressively:

  • Growling

  • Lip-lifting

  • Snapping

  • Lunging

  • Blocking of the other dog’s route

  • Staring at the other dog

Why is my dog suddenly aggressive to our other dog?

Most of the time, dog-on-dog aggression is seen in uncastrated male dogs. It is a symptom of the animal’s powerful hormonal drive to compete for reproduction. While female dogs are, on average, less likely to show dog-on-dog aggression, this doesn't mean that they are not capable of it.

Other times, aggression occurs out of fear or frustration. It’s very important to find the root cause of your pet’s aggression so that you can properly treat it. Indeed, fear aggression is very different from sex-related aggression, and so on. Again, you must remember that showing aggression between dogs is normal. It is as much a part of the dog’s life as it is the human’s.

Dog-on-dog aggression can be triggered by any dog for a variety of reasons. Some dogs have a natural tendency to look threatening; their breeding may have given them an erect posture with tall ears and a tail that is always raised (e.g. Spitz-type breeds or German Shepherds). Although not a look that is necessarily deliberate, it may spur on other dogs to respond in kind, and start posturing.

However, dog-on-dog aggression can sometimes be due to a dog’s lack of training and socialising. This is why it’s so important to socialise your puppy from a very young age. Once the problem behaviour has already set in, socialisation won’t fix it - you’ll have to go down the desensitization route instead.

A traumatic experience may also be triggering your dog. For instance, dogs that have a past in the dog-fighting industry can remain very reactive towards other dogs all throughout their lives. Cases are not always this drastic though. One bad experience with a big dog at the park and your pooch may be forever scarred. Indeed, these bad experiences may cause her to become pathologically scared of another dog’s presence, or, in other cases, over-protective of her 'property', such as her treats and toys.

Dealing with dog aggression

Knowing why your dog is being aggressive all of a sudden is a big step in knowing how to control the problem. Owners must learn how to avoid situations that encourage aggressive behaviour in the dog. In situations where aggressive behaviour is more likely to occur, the dog must be kept away from potential flashpoints. Here are a few ways by which we, as owners, can handle (and avoid) dog-on-dog aggression:

1. Don’t punish your dog for being aggressive with another dog

If your dog shows aggressive behaviour toward another dog, and is reprimanded in the form of tugging on the lead, hitting, or yelling, then your dog will not only learn to fear you, but will also associate the presence of another dog with this harsh punishment. This will in no way help your dog become more comfortable around other dogs. If your dog does show aggressive behaviour toward another dog during an on-lead walk, just remove her from the situation by walking away silently.

2. Stay calm and positive when meeting another dog

When it comes to what their owner is feeling, dogs are very good at picking up subtle signs. If we were to meet another dog while on a walk and we begin to tense up, our dog will feel the rising anxiety and will either become anxious herself or try to work out what is causing the anxiety.

Instead, stay calm, as if there is nothing to worry about, which there indeed shouldn’t be. Try to associate positive things with seeing other dogs (even from far away, especially at the start), such as receiving treats, or lots of fuss. Of course, always do this in the safest way possible, with your dog safely restrained. If she feels too uncomfortable, remove her from the situation, and try again next time. Positive reinforcement is key - always praise your dog when she behaves appropriately!

3. Outside of training sessions, avoid undue contact with other dogs

When you are out for a walk, you do not need to meet other dogs. Some owners seize the chance to talk to others but if you have a dog that is prone to aggression or is at the receiving end of aggression it is best to avoid such situations. You can take a different route and cross the street. If your dog is uncomfortable with other dogs, best to give her some space.

4. Create a void between the dogs

If crossing paths is unavoidable try to make sure there is sufficient space between both dogs. If you have dogs that are prone to sudden outbursts of aggression in the house, separate their cosy space, their beds, their food and drink bowls and avoid at all costs a situation in which they find themselves in close proximity. Baby gates may be very useful in these situations.

If you are out walking and you see an owner and their dog ahead of you, avoid walking directly towards them. Cross the road, swerve around a parked car or try to block your dog’s view of the other dog.

5. Keep dog meetings short

When your dog meets another dog while on a walk keep their meeting short. Your aim in a situation such as this is to prevent your dog from becoming so preoccupied with the other dog that she forgets you are there and, more importantly, forgets you are in charge. Interrupt her every few seconds in some way and do not linger in proximity to the other dog.

Of dogs that are prone to aggression keep them separate. 

For dogs that are suddenly aggressive to other dogs living in the same house, you may need to consider fundamental changes to your living arrangements, such as keeping the dogs in separate rooms and avoiding flashpoints throughout the day (e.g. dinner, play, cuddles and sleep). 

If all else fails and your dogs show no promise of ever being friends, you may have to consider rehoming one of the dogs. Some dogs are just more independant than most and do better in single-dog homes. Rehoming one of your dogs could relieve the whole family (dogs included) of a lot of stress. 

Final considerations

A dog that is prone to being suddenly aggressive in the house or outdoors may not have been brought up correctly. This is why it is so important to make sure you expose your puppy to as many different meetings (canine and human) as possible from a very young age! The more experience your pup has interacting with others of her kind, the less likely she is to act inappropriately with them when she is older.

Puppy classes may not be everyone’s cup of tea but they are a supremely effective way to get your dog used to meeting other dogs in a controlled way. For juvenile dogs, lessons of etiquette teach the dog what is expected of her behaviour when she meets another dog.

Keep in mind that if your dog is already showing dog to dog aggression, you should absolutely seek out a professional dog trainer/behaviourist. These professionals can help you work on desensitizing your dog to other dogs, all in the safest and most effective way possible.

Finally, it's important to note that in some cases, sudden aggression might be a big red flag that your dog is in pain, possibly due to an undiagnosed medical condition. Be sure to consult a vet before ruling out this possibility.

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