You’re looking at a photo of a st bernard mastiff mix puppies litter and thinking, "Wow, those paws are the size of dinner plates." You aren't wrong. These dogs, often called Saint Bermastiffs, are absolute units. But before you go dropping a deposit on a pup that looks like a fluffy marshmallow with a droopy face, we need to talk about the reality of living with a dog that can literally outweigh a grown man.
Giant breeds aren't for everyone. They just aren't.
Most people see the "Nanny Dog" vibe of the Saint Bernard and the "Guardian" stoicism of the English Mastiff and assume they're getting a gentle giant that sits quietly by the fireplace. Sometimes that happens. Other times, you get a 170-pound wrecking ball that doesn't realize it can't fit on your lap anymore. Honestly, the variability in these crossbreeds is wild because you're mixing two distinct histories of working dogs. One was bred to find people buried in Swiss alpine snow; the other was bred to guard English estates from intruders. When those genetics collide in a puppy, you get a beautiful, slobbery mystery.
The Reality of the Saint Bermastiff Size and Growth
Growth is aggressive. Not aggressive in personality, but in scale. A st bernard mastiff mix puppies growth curve is a vertical line. By six months, your "puppy" might already weigh 80 pounds. By a year, they’re pushing 120. They don't actually stop filling out until they are about three years old. This slow maturation is vital to understand because their bones and joints are under immense pressure during those first 24 months.
If you let a Saint Bermastiff puppy run up and down stairs or jump off a high truck bed, you are asking for orthopedic disaster. Their growth plates are soft. Veterinary orthopedic surgeons, like those at the Cornell University College of Veterinary Medicine, often emphasize that giant breed puppies need controlled exercise. Short walks are great. High-impact agility? Save that for the Border Collies.
Feeding is another beast. You can't just grab a bag of "puppy food" from the grocery store. Giant breed formulas are non-negotiable here. Why? Because the calcium-to-phosphorus ratio has to be precise. If they grow too fast, they develop conditions like Panosteitis (wandering lameness) or Hypertrophic Osteodystrophy (HOD). It’s painful for the dog and expensive for your wallet. You basically need to be a part-time nutritionist for the first two years of their life.
Temperament: Is the St Bernard Mastiff Mix Actually a Good Family Dog?
Usually, yes. They are famously affectionate.
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But here’s the thing—they are also stubborn. The Mastiff side often brings a "What's in it for me?" attitude to training. Unlike a Golden Retriever who lives to please you, a Saint Bermastiff might look at your "sit" command, look at the floor, decide it’s too much effort to move that much mass, and just keep standing. You need patience. Lots of it.
Socialization is the most important thing you will ever do. A 150-pound dog that is fearful or protective because it wasn't exposed to strangers is a liability. It isn't just about being "nice." It’s about being bomb-proof. They need to see umbrellas, hear sirens, meet people in hats, and watch kids on bicycles. Because if a Saint Bermastiff decides to lung at something, you aren't holding them back. You’re just a passenger on the other end of the leash.
They tend to be lower energy than most people expect. They are the kings of the "sploot." You’ll find them sprawled across the kitchen floor, usually in the exact spot where you need to stand to reach the stove. They don't need five-mile hikes. They need a solid 30-minute sniff-walk and a backyard to patrol. If you live in an apartment, it can work, but only if you have an elevator. Carrying a lame 150-pound dog down three flights of stairs is physically impossible for most humans.
Health Concerns You Can't Ignore
We have to talk about the "B" word: Bloat.
Gastric Dilatation-Volvulus (GDV) is the number one killer of giant breeds. The stomach fills with gas and twists, cutting off blood supply. It is a true emergency. Many owners of st bernard mastiff mix puppies opt for a "gastropexy" (stomach tacking) surgery when the dog is neutered or spayed. It’s a preventive measure where the surgeon stitches the stomach to the abdominal wall so it can’t flip. It’s an extra cost, but it saves lives.
Then there are the joints. Hip and elbow dysplasia are common in both parent breeds. When looking for a puppy, you absolutely must ask for OFA (Orthopedic Foundation for Animals) or PennHIP scores from the parents. If the breeder says "the parents look healthy" but has no paperwork, walk away. Actually, run. A cheap puppy from a backyard breeder will cost you $10,000 in surgeries by age five.
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- Entropion/Ectropion: Eye issues where the lids roll in or out.
- Dilated Cardiomyopathy (DCM): Heart health is huge. Keep them lean to reduce strain.
- Lifespan: You’re looking at 8 to 11 years. It’s the "short time, big love" trade-off.
The "Slobber Factor" and Home Maintenance
If you are a neat freak, stop reading and go look at Poodles.
The Saint Bermastiff has "jowls." These are essentially gravity-fed slime dispensers. When they drink water, they don't just swallow it; they take a gallon into their mouth and then distribute half of it across your hardwood floors as they walk away. You will find dried "shmoo" on your walls, your ceiling, and your nice clothes. Most owners keep "drool rags" in every room of the house.
Shedding is also a factor. The Saint Bernard side usually brings a thick double coat. They "blow" their coat twice a year, which means your vacuum cleaner is going to be fighting for its life. Regular brushing helps, but you're still going to find tumbleweeds of fur in the corners of your dining room.
Training Needs and Positive Reinforcement
Force-based training does not work with these dogs. If you try to bully a Mastiff mix, they will shut down. They become statues.
The most effective way to train a st bernard mastiff mix puppies is through high-value rewards and relationship building. Use chicken. Use cheese. Start the day you bring them home. Loose-leash walking is the priority. Again, you cannot physically restrain this dog if they decide to bolt. They must choose to walk with you because they enjoy your company (and the treats in your pocket).
Be prepared for the "Teenage Phase." Between 8 and 18 months, they will test every boundary you’ve set. They’ll "forget" their potty training or suddenly decide they don't know what "stay" means. Stay consistent. They are just big toddlers with more muscle than brains at that stage.
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Finding a Responsible Breeder or Rescue
Don't buy these dogs from pet stores. Ever. Those puppies almost exclusively come from puppy mills where health testing is non-existent.
If you want a puppy, look for breeders who focus on temperament and longevity. They should be able to show you where the dogs live (hint: it shouldn't be a cage). A good breeder will interview you more than you interview them. They want to make sure you have the space and the financial stability to care for a giant.
Alternatively, check breed-specific rescues. There are plenty of Saint Bernard and Mastiff rescues (like the Gentle Giants Rescue) that often have mixes. Many of these dogs are "teenage" surrenders—people who got a cute puppy and realized they couldn't handle a 130-pound dog that eats $100 worth of food a month. Adopting an adult gives you a clearer picture of their health and personality.
Actionable Steps for Future Owners
If you're serious about bringing one of these giants home, you need a plan that goes beyond buying a leash and a bowl.
- Budget for the "Giant Tax": Everything costs more. Heartworm prevention for a 150-pound dog is triple the price of a Lab’s. Boarding is more expensive. Vet bills are higher because sedation and medication doses are based on weight.
- Audit Your Vehicle: A Saint Bermastiff isn't fitting in the back of a Mini Cooper. You need an SUV or a van with a low load floor. Many owners eventually buy ramps so the dog doesn't have to jump in and out, protecting those joints.
- Find a "Giant-Friendly" Vet: Not all vets are comfortable or experienced with the specific anesthesia needs of giant breeds. Find one who knows their way around a Mastiff’s heart and a Saint’s joints.
- Proof Your House: Move the breakables off the coffee table. A single happy tail wag can clear a surface in seconds. Also, get a raised slow-feeder bowl to help prevent gulping air, though the research on whether raised bowls help or hurt bloat risk is still debated—talk to your vet about the latest findings.
- Commit to the First Two Years: This is the "infrastructure" phase. Focus 100% on joint health, slow growth, and massive socialization. If you get the foundation right, the next decade with your Saint Bermastiff will be the most rewarding experience of your life.
These dogs are massive commitments, but they offer a level of companionship that is hard to find elsewhere. They are soulful, observant, and deeply tied to their "pack." Just make sure you’re ready for the slime.