Why Is My Dog Attacking My Other Dog All Of A Sudden?

Like human siblings who squabble over toys or vie for parental attention, dogs sharing a household can experience their own form of sibling rivalry. When dogs suddenly start fighting or exhibiting aggressive behavior towards each other, it can leave pet owners concerned and confused, especially if they once coexisted in harmony.

Unexpected altercations between dogs can happen for various reasons, from developmental changes to competing for resources. While these conflicts can be jarring, identifying the root cause is essential if you want to restore peace in your household and ensure all your furry family members are happy and healthy.

Common Reasons for Cohabiting Dogs to Start Fighting

We spoke to a variety of experts on the topic, including dog behavior specialists and vets, to explore why dog fighting happens and what you can do to change it.

Shifting Dynamics, Hormonal Changes, or Health Issues

The most common explanation for why dogs might start fighting is that a shift in their dynamic occurs. This is common with hormonal changes that lead to resulting power changes, but there are other reasons that issues can bubble up.

Nicole Ellis, a certified professional dog trainer and pet lifestyle expert with Rover, shares, “Just because dogs got along once doesn’t mean they always will. Dynamics can shift over time — one dog grows more confident, another more fragile, and what used to be tolerated might become intolerable. Peaceful coexistence can be a phase, not a promise. Changes in hormones (especially as one hits adolescence or goes intact), pain, or illness are often causes that also often go unnoticed, or the slow buildup of unaddressed tension can tip the balance.”

Changes in the Environment or Their Routine

External changes outside the dogs’ relationships, like in their routine or home setting, can also impact them — think moving to a new house, bringing a new pet or baby into the home, undergoing noisy renovations, or changing your work schedule.

Dogs are creatures of habit who thrive on predictability, and when you make major changes in those habits, it can make them feel unsettled, leading to heightened stress levels and potential conflicts. To combat this, provide your dogs with as much additional structure and exercise as possible.

Resource Guarding

Dogs might compete for resources like food, beds, and toys, but Ellis shares that even attention can be a resource. If you regularly give more attention to one dog, the other might suddenly “guard” their access to you due to jealousy. If a dog perceives that another is threatening one of their resources, they can respond with aggression, even if they’ve been able to share in the past.

One reason early socialization is so important — and a common critique of removing puppies from their littermates too soon — is that dogs may miss out on developing key social skills. Without these skills, they can struggle to read other dogs’ cues and have trouble getting along later, leading to conflicts.

Poor Conflict Resolution

Early socialization is key for young dogs, and for those who don’t get it, this often manifests in an inability to handle conflict appropriately. Small disagreements can turn into a full-blown fight if a dog hasn’t learned these skills and escalates the situation too quickly.

Philip Tedeschi, human-animal connection expert with Rover, tells us, “One of the reasons to give young dogs plenty of early socialization, or even a critique of removing a dog from their littermates early, is that they fail to gain these necessary social skills that can show up later in terms of difficulty getting along and/or reading cues from other dogs resulting in conflicts. Older dogs can become increasingly frustrated or defensive in the face of constant play, bumping, competition, or jealousy, especially if they’re experiencing pain from the onset of arthritis.”

How to Restore Peace in Your Household

First things first: A tired dog is a happy dog. If your dog isn’t being sufficiently stimulated mentally and physically, it can be extremely detrimental to their well-being. A bored dog can experience mood changes and become destructive or aggressive with other dogs in the household.

If you need to be out of the house for more than six hours at a time, Ellis recommends hiring a dog walker, mentioning that in Sweden, citizens aren’t allowed to leave their dog alone for longer than six hours. When spending time with your dog, play games with them and take them on as many adventures as possible. For a younger dog with lots of energy, this might mean longer walks, a hike, or extended playtime with a ball and a Chuckit!

The next step is ensuring that clear leadership, boundaries, and training have been implemented. Training acts as a communication tool between humans and dogs, and harsh or punitive measures don’t convey expectations effectively. Ellis says, “Imagine your dog is excited to meet another dog and greet them or make a new friend, and what they routinely experience is your frustration at their excitement by harshly verbally reprimanding them or yanking their leash. Your dog might not only find this confusing and stressful, but also begin to associate the desire to interact with another dog as distressing.”

If the issue is resource guarding, consider feeding dogs separately and removing high-value toys if these hot commodities are the source of conflict. When dogs successfully share resources, reward this behavior. Teaching commands like “leave it” and “drop it” also reinforces the need for training, as these simple phrases can help defuse tension.

For dogs with poor conflict resolution skills, practice calm obedience skills and impulse control exercises. Working with a qualified dog behaviorist or trainer can help if you’re unsure where to start.

Finally, suppose you’re concerned that sudden aggression is due to a medical condition or your dog is experiencing pain. In that case, Dr. Aimee Warner, resident veterinarian at Waggel, shares advice on what to keep an eye out for. Warner says, “Check for small indications, which include limping together with flinching when touched and changes in appetite and avoidance behaviors. Before attributing aggression to behavioral issues, you should schedule a veterinary examination to determine if physical problems exist.”

She adds that unneutered male dogs or unspayed female dogs in heat can have elevated hormone levels that work as “intensity boosters” and increase aggression in conflicts. Getting your dog neutered or spayed should be combined with proper socialization and training, which can minimize these effects.

Understanding Canine Body Language

Along with training your dog, knowing their body language is an essential part of understanding them and avoiding a fight before it happens. Dogs are always communicating with us, and since they can’t vocalize their feelings, it’s essential that we know how to read them.

Tedeschi says to watch for signs of strong physical tension, such as tight lips and sustained snarling, stiff bodies, and difficulty disengaging from the situation. If your dog is completely still, giving another dog a hard stare, or blocking the other dog from accessing a doorway, couch, or human, something bigger could be brewing. As the dog owner and leader, it’s your job to be aware of these moments, catching and redirecting them to prevent fights.

What To Do if Your Dogs Are Fighting

To safely intervene in a fight, avoid grabbing collars, which may result in a bite. Ellis recommends using distraction tools like loud noises, a broom to separate them, or citronella or water spray. That said, if your dog gets into a serious fight, intervening can be dangerous, and most people don’t have the proper training to intervene.

Instead of figuring out how to stop dog fighting, the best thing you can do is to interrupt the tension before it becomes a fight, redirecting with cues or calling them apart calmly but with authority. Awareness, prevention, and early intervention are your best (and safest) bet to avoid getting hurt.

Most Relationships Can Heal

While conflicts can be upsetting, most dogs can recover if the owner invests time and work to reshape the relationship with the right boundaries and tools. Hiring a trainer can also help, but maintaining consistency at home is vital, as is properly understanding your pets’ body language.

Recognizing the issue and implementing the appropriate solutions (as outlined here) will make a difference. Try not to over-excite your dogs if you’re dealing with these issues, and exercise them individually to take the edge off their energy level. Finally, Ellis recommends ending each interaction on a success so that it normalizes and imprints a new positive pattern.