Are Bullmastiffs good with cats?

Why Bullmastiffs struggle with cats

Bullmastiffs have instincts that make cat cohabitation a real risk. Whether it's a high prey drive, territorial behaviour, or simply the low energy level that leads to relentless harassment, the combination often doesn't end well for the cat.

The loyalty these dogs have toward their family sometimes extends to other animals in the household, including cats they've known from an early age. A naturally calm dog reduces the daily stress level in a shared home. Cats settle around dogs that are settled. The baseline energy matters more than most people expect. Protective instincts sometimes redirect toward the cat in the form of resource guarding, especially around food bowls, beds, or favoured spots near the owner. Devoted dogs sometimes view the cat as a rival for owner attention. Not aggression, but friction, particularly early on when the cat disrupts established routines.

Even without intending harm, a Bullmastiff that constantly chases a cat causes chronic stress — which has serious health consequences for cats. A dog doesn't need to injure a cat to make the cat's life miserable.

The size factor with Bullmastiffs

At 41–59kg, a Bullmastiff can cause serious injury to a cat even unintentionally — physical size makes every incident higher stakes.

Be honest about this before committing to keeping both. The question isn't just "will they get along?" but "what happens when they don't?" The answer changes significantly depending on the physical size of the dog involved.

Training won't fully solve it

Training Bullmastiffs requires consistent effort. A "leave it" command and reliable recall are achievable, but they need repetition and patience to make stick. The good news: it is achievable.

Even the most well-trained Bullmastiff will still have prey instincts — training suppresses the behaviour in controlled situations, but cannot remove the underlying drive. A startled dog, a running cat, a moment of inattention — these are the situations where training alone isn't a reliable safeguard.

Stress in the shared home

Their naturally quiet temperament is a plus in a mixed household — Bullmastiffs are unlikely to alarm a cat with sudden loud barking, which reduces general stress levels for both animals.

Cats under chronic stress show it through hiding, reduced appetite, changes in litter box behaviour, and over-grooming. A cat that "seems fine" but spends most of its time in one room, avoids the dog's areas, and rarely relaxes fully is not fine — it's managing a situation it has no good way out of.

When it might work

Exceptions exist. Some individual Bullmastiffs — particularly those raised alongside cats from puppyhood — develop a genuine tolerance or even friendship. The key factors that improve the odds:

• Dog and cat raised together from very young ages
• The specific dog has a lower-than-typical prey drive for the breed
• The cat is confident and not a runner (running always triggers chase instinct)
• Permanent separation capability if things don't work out

If you have both, do this

Never leave them unsupervised until you are absolutely certain the dog will not chase. Even then:

• The cat must always have escape routes the dog can't follow
• Baby gates give the cat safe zones throughout the house
• Separate feeding areas and litter tray in a dog-free space
• Be honest about whether the cat is stressed. A cat hiding permanently is not "fine"

The most important question to ask yourself honestly is whether you can permanently commit to a home setup that keeps both animals safe. This means baby gates that stay up for years, not weeks. It means a cat with reliable access to at least one room the dog can never enter. It means routine supervision, not occasional supervision. Many people start with good intentions and let the arrangement slip — with consequences that are hard to undo.

If you're getting a Bullmastiff puppy into a home that already has a cat, you have the best possible starting point — puppies socialised with cats early are far more likely to develop a genuine tolerance than dogs introduced to cats later in life. Even then, the breed's natural instincts don't disappear; they require active management and a home layout that protects both animals throughout the dog's life. With a lifespan of 7–9 years, you're committing to that management for a long time.