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Why Is One Of My Dogs Aggressive To The Other? (Solved)

Having dogs that get along with each other well is critical for a happy home. So, what happens when dogs who were once great friends suddenly start to fight?

This article explains everything you need to know.


Signs of Canine Aggression To Look Out For

You may think it is always easy to tell when a dog is showing aggression towards another. However, signs can be subtle and are often missed by less experienced owners. It can help to learn more about canine body language; so you know what to look out for.

The obvious and best-known signs of aggression include growling, snapping, lunging, and biting.

However, there are plenty of additional signs a dog can show before it escalates to this point. These include:

  • Staring directly into the other dog’s eyes
  • Slowing ‘whale eyes’. This is when the whites of the eyes are more visible than usual
  • Freezing still
  • Stiff tail movements or abrupt tail wags
  • Lip curling
  • Teeth baring

If your dog is becoming angry and hostile towards their four-legged companion, it is important you notice the warning signs before a fight breaks out.

10 Reasons Why One Dog Becomes Aggressive To The Other

There is a wide range of reasons that dogs who once got along swimmingly will suddenly have a falling out. Sometimes, you need to play the role of detective, thinking back to before the fight, to determine why it broke out.

1. Resource guarding

This is one of the most common triggers. While dogs are pack animals and are usually good at sharing their resources, this is not always the case. We see most issues when it comes to items that are perceived to hold a high value. 

Things like bones, long-lasting chews, and ‘favorite’ toys may be a point of contention. Even the best ‘spot’ on the sofa can be fought over. Take a look around the room during a tussle; are there any items nearby that your dogs may have been fighting over?

2. Over excitement

Some dogs find it hard to channel their energy when their adrenaline is pumping. If your other dog is in the wrong place at the wrong time, they may become a target for all of that pent-up excitement.

This sort of thing can happen on walks in those who get amped up to be outside, perhaps if they’ve gone a little longer than they should have before being brought out. This is especially true if they feel restrained when on their lead.

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3. Previous bad experiences

It’s not only elephants that have good memories. If your dogs have fought in the past, they are more likely to lock horns again. When a fight happened recently, dogs are often on edge and waiting for something to kick off.

4. Getting Startled

It isn’t uncommon for one dog to scare another by e.g. yelping loudly or sneaking upon them. Some dogs will react by suddenly snapping, which may give both canines a fright!

Older dogs whose hearing and eyesight have declined will tend to startle a lot easier. 

5. Stress at home

A lot of dogs are naturally sensitive souls. They need a calm environment in order to keep stress levels low. If there is turmoil within the home, this can lead to high levels of anxiety in your four-legged friends.

Raised voices, lots of new people about or the arrival of a new pet or baby could make for a dog that is on edge. Any new stressor could be the reason for a dog to lash out.

6. Anxiety inducing events

For some dogs, things like local construction work, fireworks, or a storm are their idea of hell. They may get so anxious that they find it hard to cope and might become aggressive if another dog approaches.

These dogs may show additional signs of stress including whining, panting, and trembling.

7. Reduced exercise

Perhaps the weather is getting colder or you’ve sustained an injury and are less able to walk your dogs. Or maybe your country has gone into (yet another!) lockdown and you’re forced to stay home.

Less opportunity for dogs to expend their energy is a recipe for disaster, especially in those who can be more highly strung such as Collies, German Shepherds, and Spaniels.

Leaving your dogs alone for prolonged periods and not giving them enough to do is also a recipe for disaster.

8. Illness or injury

If your dog is suddenly acting completely out of character, consider that there may be a medical issue. Dogs who feel unwell or are in pain can become very defensive all of a sudden.

These dogs may choose to hide away and become aggressive if another dog encroaches on their ‘hiding spot’. They may also lash out if another dog bumps against them, causing pain.

9. Old age

If your dog has always been tolerant but starts lashing out in their old age, this is not uncommon. Dogs become less tolerant as they get older, especially when young and energetic pups are about.

The combination of hearing and sight loss alongside the start of painful issues such as arthritis can make some older dogs a bit grumpy. It is always important to have your older dog examined by a vet routinely.

Snappiness or a reduced tolerance tells us something is up with our golden oldie. If suffering from joint pain, most will benefit from prescription medications such as anti-inflammatories and pain relief. For most, once their pain is controlled, the improvement is dramatic.

10. Hormonal

If your dogs aren’t neutered, sex hormones may be at play here. Females in season, who are pregnant or who have recently given birth can be more aggressive. Also, males who’ve caught the scent of a female in season can become hyper-aroused.

In multi-dog households, when not breeding, it is often easiest to have the dogs neutered once they have matured physically. Otherwise, you need to keep females well away from males once in season.

Anecdotally, uncastrated males are naturally more aggressive. This seems to be true in some breeds more than others, including the Cane Corso, Mastiffs, and Akitas. These are naturally ‘protective breeds’.

If you have two males, the dog to dog aggression can become a huge issue for some. Talk to your vet first, but neutering is often part of the solution.

How To Help Your Dogs Get Along Better

The first step in reducing canine aggression is to identify the cause of the outburst. Once the trigger is discovered, implement a plan so that your dog’s environment is managed going forward.

All family members must be on the same page and should stick to the plan. We cannot expect an instant fix but, with time, we should be able to prevent the aggression from occurring the majority of the time.

Regardless of the issue, it is always sensible to consult a canine behaviorist. Indeed, a good one is worth their weight in gold and can help set you on the right track from day one. Your vet will be able to direct you to a local behaviorist that comes recommended.

Get good at monitoring your pets’ body language. This will allow you to step in before any escalation; ensuring it never gets to the point of a physical fight.

Regardless of age and breed, all dogs need exercise. If enough is not provided, dogs can get a little ‘stir crazy’. Keep activities fun and varied, going on different hiking routes and allowing your dog to sniff and explore.

If you don’t have the time to bring your dogs out, hire someone else to do it for you. Dog walkers are a great solution when you’re working or away from the home. Another option would be doggy day-care.

As well as giving your dog physical activities to do, provide plenty of mental stimulation. A bored dog is more likely to be an unhappy one. Offer a range of brain games and training opportunities to keep your dogs content.

Remember, training is not just for puppies. Keep up lots of positive reward-based training, building confidence and trust in your dogs. All dogs love to ‘get it right’ and get a real endorphin rush from a good training session.

Consider using physical barriers within your home. Things like crates can be really useful if you have crate-trained dogs. Equally, stair gates and baby gates can provide ‘safe zones’ where dogs know they can relax without being disturbed.

This is especially important for older dogs who are finding it hard to tolerate a more rambunctious youngster. Barriers are also key when it comes to feeding dogs that can resource guard.

Be sure to provide equal care and attention, to avoid jealousy. Even if one of your dogs puts on a hard front, they still crave your companionship and input. Don’t spend all your time with your needier dog, as this can lead to envy.

If one of your dogs is not a sharer, make sure they are not forced to resource share. This will mean feeding separately, providing individual bowls and toys and managing your dog’s space well.

It is key that any underlying anxiety is well managed. This may entail natural calming supplements, pheromone releasing plug-ins, prescription medicine, and behavioral modification programs.

Some dogs are genetically more prone to anxiety or may have had a stressful start in life. These dogs need some extra TLC and veterinary input in order for them to relax and settle.

Implement a solid and predictable routine. While it can sound boring to feed and walk your dogs at the same time every day, they thrive on consistency. For some, a manic routine can cause their anxiety to build.

Remember, a calm and anxiety-free dog is much less likely to be reactive or aggressive. When combatting aggression, we need to take a look at our dog’s lifestyle as a whole.

Rule Out Health Issues

Don’t forget that sudden aggression is commonly caused by medical issues. This is true regardless of breed, sex, and age.

Any source of pain can result in a short fuse and a tendency to snap or growl. This can mean anything from a sore back tooth or ear infection to joint disease, an anal gland abscess or abdominal ache. 

Some dogs are good at hiding signs of illness, so an unexpected change in behavior always warrants a vet check.

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Before making any decisions that could affect the health and/or safety of your dog, you should always consult a trained veterinarian in your local area. Even though this content may have been written/reviewed by a trained veterinarian, our advice to you is to always consult your own local veterinarian in person. Please read our full dislcaimer if you have any questions.