St Bernard Mixed with Mastiff: The Gentle Giant Crossbreed Guide

If you've been searching for a truly massive companion dog with a gentle soul, the St Bernard mixed with Mastiff — sometimes called the "Saint Mastiff" or "Mastiff Bernard" — might have crossed your radar. This designer crossbreed combines two of the largest dog breeds on the planet, and the result is a dog that can easily tip the scales past 150 pounds. But before you commit to sharing your home (and your couch) with a canine of this magnitude, you need to understand exactly what you're signing up for.

Designer mixes between giant breeds carry unique considerations that smaller crossbreeds simply don't. Joint stress, feeding costs, space requirements, and lifespan realities all demand honest evaluation. In this guide, I'll walk you through everything you need to know about the St Bernard mixed with Mastiff — from predictable traits to the variables that can make each individual dog quite different from the next.

The Parent Breeds: St. Bernard and Mastiff

Understanding any mixed breed starts with understanding the two parent breeds. Both the St. Bernard and the Mastiff have centuries of history, and their traits heavily influence what you'll see in their offspring.

Parent Breed Comparison: St. Bernard vs. Mastiff (English Mastiff)

Trait	St. Bernard	English Mastiff
AKC Group	Working Group	Working Group
Weight Range	140–180 lb (64–82 kg)	120–230 lb (54–104 kg)
Height	26–30 in (66–76 cm)	27.5–30+ in (70–76+ cm)
Coat Type	Short smooth or long rough	Short, dense, straight
Shedding Level	Moderate to heavy (seasonal blowout)	Moderate, year-round
Lifespan	8–10 years	6–10 years
Energy Level	Low to moderate	Low
Drooling	Heavy	Moderate to heavy
Original Purpose	Alpine rescue, draft work	Guardian, war dog, estate protector
Temperament Core	Gentle, patient, eager to please	Calm, courageous, dignified

The St. Bernard originated in the Swiss Alps, where monks at the Great St. Bernard Hospice bred them for search-and-rescue work in treacherous mountain passes. Their famous barrel of brandy is a myth (popularized by an 1820 painting), but their lifesaving instinct is very real. The English Mastiff traces back to ancient Britain, where they served as war dogs, estate guardians, and even fought in Roman arenas. Today's Mastiff is far removed from those combat origins — they're famously gentle with their families.

How Big Will a St Bernard Mixed with Mastiff Get?

This is the question every prospective owner asks first, and honestly, the answer requires some mental preparation. Both parent breeds are giants, so this mix will be enormous — but exactly how enormous varies.

St Bernard × Mastiff Size Range Estimates

Category	Low End	High End
Adult Male Weight	140 lb (64 kg)	230+ lb (104+ kg)
Adult Female Weight	120 lb (54 kg)	180 lb (82 kg)
Height at Shoulder	26 in (66 cm)	32 in (81 cm)
Full Maturity Age	18 months	24–30 months

Giant breeds grow slowly. Your St Bernard mixed with Mastiff puppy won't reach full skeletal maturity until 18 to 30 months of age. During the growth phase, it's critical to feed a large-breed puppy formula — look for AAFCO statements specifying "growth" or "all life stages" with the large-breed growth qualifier. Brands like Purina Pro Plan Large Breed Puppy, Royal Canin Giant Puppy, and Hill's Science Diet Large Breed Puppy are formulated to slow growth rate and reduce orthopedic disease risk.

Keep your puppy lean during growth. Research published in the Journal of the American Veterinary Medical Association has demonstrated that overfeeding giant-breed puppies significantly increases the risk of hip dysplasia and other developmental orthopedic diseases. Aim for a body condition score (BCS) of 4/9 throughout growth — you should easily feel ribs without pressing hard, and see a visible waist from above.

Understanding Generations: F1, F1B, and Beyond

Unlike Poodle mixes (Labradoodles, Goldendoodles) where multigenerational breeding programs are well-established, the St Bernard mixed with Mastiff is almost exclusively produced as an F1 cross. You'll rarely find F2 or multigen litters because the market demand isn't large enough to sustain dedicated multi-generation breeding programs.

What this means for you: most puppies you encounter will be F1s, and each puppy in a litter may inherit a different combination of parent breed traits. One puppy might look almost entirely like a St. Bernard with a rough coat, while a littermate might be the spitting image of a Mastiff with a fawn short coat. This is normal and expected for first-generation designer crosses.

Temperament: What to Expect (and What Might Surprise You)

Both parent breeds share some wonderful temperament traits — they're generally calm, loyal, and deeply bonded to their families. But combining two giant guardian breeds also introduces variables you need to plan for.

Best-Case Temperament Scenario

Your Saint Mastiff inherits the St. Bernard's eager-to-please attitude and the Mastiff's calm confidence. The result is a dog that's gentle with children, welcoming (if reserved) with guests, easygoing in the home, and responsive to training despite a mild stubborn streak. Think of a 170-pound dog that considers itself a lap companion and greets visitors with a wagging tail and a leaned-against-their-legs hello.

Challenging Temperament Scenarios

Some individuals may lean heavily into the Mastiff's guardian instincts, becoming protective of the home and wary of strangers. This isn't aggression — it's a deeply ingrained territorial instinct. Without proper socialization during the critical 3-to-14-week window, a protective giant dog becomes a management challenge. A 180-pound dog that doesn't want visitors entering your home is not something you can physically restrain.

Additionally, both breeds can be stubborn. The St. Bernard was bred to make independent decisions in avalanche rescues, and the Mastiff was bred to assess threats without waiting for commands. This independence can manifest as selective hearing during training sessions.

Socialization and Training Essentials

Start socialization early and keep it positive. Giant breeds have a shorter socialization window than smaller dogs because they mature more slowly, but the urgency is higher — you simply cannot manage an unsocialized 200-pound dog. Enroll in a force-free puppy kindergarten class by 10–12 weeks of age (after your veterinarian clears your puppy for controlled group exposure post-vaccination).

Use positive reinforcement exclusively. Food motivation tends to be strong in both breeds, which works in your favor. Avoid any aversive training methods — shock collars, prong collars, and alpha rolls are inappropriate for any dog, but especially counterproductive with giant breeds where fear-based reactions at that size become safety hazards. Look for trainers certified through the Certification Council for Professional Dog Trainers (CCPDT) who use LIMA (Least Intrusive, Minimally Aversive) methodology.

Coat, Shedding, and Grooming Realities

Is the St Bernard mixed with Mastiff hypoallergenic? No. Neither parent breed carries the low-shedding gene, and this mix will shed — the only question is how much.

Coat Possibilities in the St Bernard × Mastiff Cross

Coat Type	Inherited From	Shedding Level	Grooming Frequency
Short, dense, smooth	Mastiff (more common)	Moderate, year-round	Brush 2–3× weekly
Medium-length, slightly wavy	Blend of both	Moderate to heavy	Brush 3–4× weekly
Long, rough, dense	St. Bernard (rough coat)	Heavy, seasonal blowout	Daily brushing during shed season

Most F1 puppies inherit a short-to-medium coat closer to the Mastiff's, since short hair is generally dominant. However, if the St. Bernard parent is the rough-coated variety, you might get a medium-length coat with feathering on the legs, chest, and tail.

Grooming Toolkit for This Mix

• Undercoat rake or de-shedding tool: The Furminator for Large Dogs (short or long hair version depending on coat) works well for seasonal blowouts. Use weekly during spring and fall.
• Slicker brush: For medium or longer coats, a large slicker brush handles tangles in feathering areas.
• Rubber curry brush: For short-coated individuals, a Kong ZoomGroom is excellent for daily quick passes and distributes natural oils.
• Nail grinder: Giant breeds need nail maintenance every 2–4 weeks. A Dremel 7300-PT or the Casfuy Dog Nail Grinder is safer than clippers for thick giant-breed nails.
• Drool management: Keep drool rags handy. Both parent breeds drool, and your mix likely will too — especially after drinking, eating, or in warm weather. Wipe facial folds daily to prevent moisture-related skin infections (intertrigo).

Health Considerations: The Hybrid Vigor Myth vs. Reality

Let me be direct: hybrid vigor does not eliminate health risks in this mix. The concept of heterosis (hybrid vigor) is real in animal breeding, but it primarily benefits traits controlled by many genes (polygenic traits) and reduces the expression of recessive inherited disorders that are breed-specific. It does not magically protect against conditions that both parent breeds share.

Unfortunately, the St. Bernard and the Mastiff share several health vulnerabilities, and your crossbreed puppy can inherit any of them.

Health Conditions of Concern in the St Bernard × Mastiff Cross

Condition	Shared Risk?	Prevalence Notes	Screening Recommendation
Hip Dysplasia	Yes — both breeds	St. Bernard: ~47% affected (OFA data); Mastiff: ~14%	OFA or PennHIP evaluation of both parents
Elbow Dysplasia	Yes — both breeds	Common in giant breeds generally	OFA elbow evaluation of both parents
Gastric Dilatation-Volvulus (Bloat/GDV)	Yes — both breeds high risk	Deep-chested giant breeds; lifetime risk estimated 5–20% in susceptible breeds	Discuss prophylactic gastropexy with your veterinarian
Dilated Cardiomyopathy (DCM)	Yes — both breeds	St. Bernard predisposed; Mastiff also at elevated risk	Cardiac evaluation, annual auscultation
Osteosarcoma (Bone Cancer)	Yes — both breeds	Giant breeds carry significantly elevated risk	Monitor for lameness; early radiographs if suspicious
Entropion/Ectropion	Yes — both breeds	Eyelid conformation issues common in loose-skinned giants	Ophthalmologist evaluation (OFA/CERF)

Bloat: The Emergency You Must Prepare For

Gastric dilatation-volvulus (GDV), commonly called bloat, is a life-threatening emergency that kills within hours if untreated. Both St. Bernards and Mastiffs are among the highest-risk breeds. Your crossbreed inherits a deep, narrow chest conformation that predisposes to this condition.

Risk reduction strategies:

• Feed 2–3 smaller meals per day instead of one large meal
• Use a slow-feeder bowl (the Outward Hound Fun Feeder in XL works for giant breeds) to prevent rapid eating
• Avoid vigorous exercise for 60 minutes before and after meals
• Do not elevate food bowls — research from a study published in JAVMA found that elevated feeders actually increased bloat risk in large and giant breeds
• Ask your veterinarian about prophylactic gastropexy — a surgical procedure that tacks the stomach to the abdominal wall to prevent rotation. This can be done during spay/neuter and reduces GDV risk by approximately 95% (though it does not prevent gastric dilatation itself)

Recommended Health Testing for Parent Dogs

If you're purchasing from a breeder, insist on seeing documented health clearances for both parents. According to the Orthopedic Foundation for Animals (OFA), responsible breeders of giant breeds should provide:

• Hip evaluation (OFA Excellent/Good/Fair or PennHIP DI ≤ 0.60)
• Elbow evaluation (OFA Normal)
• Cardiac evaluation by a veterinary cardiologist
• Ophthalmologist evaluation (CERF/OFA Companion Animal Eye Registry)
• Thyroid panel (autoimmune thyroiditis screening)

Always consult your veterinarian about a health monitoring plan specific to your giant-breed dog.

Lifespan, Costs, and the Financial Reality

I want to be transparent about both lifespan and costs, because giant breeds require a different kind of financial planning than smaller dogs.

Expected Lifespan

The St Bernard mixed with Mastiff typically lives 7 to 10 years. This is the difficult reality of giant breeds — they age faster and have shorter lifespans than smaller dogs. Some individuals may reach 11 or 12 years, but this is the exception rather than the norm. Osteosarcoma and cardiac disease are the most common causes of premature death in giant breeds.

Purchase Price and Acquisition

Acquisition Cost Ranges for St Bernard × Mastiff

Source	Price Range	Notes
Responsible breeder (health-tested parents)	$1,500–$3,500	Includes health clearances, early socialization, take-back clause
Backyard breeder / online listing	$500–$1,500	Typically no health testing; higher risk of inherited conditions
Rescue / shelter	$100–$500	Rare to find this specific mix; check giant breed rescues like Saint Bernard Rescue Foundation or Mastiff Club of America Rescue

Annual Care Cost Estimates

This is where giant breed ownership hits hard. Budget realistically:

• Food: $1,200–$2,400/year. A 170-pound dog eats approximately 8–12 cups of high-quality kibble daily. Premium large-breed formulas (Purina Pro Plan Large Breed, Royal Canin Giant Adult, Orijen Large Breed) cost $60–$100 per 30-lb bag.
• Preventive medications: $600–$1,200/year. Heartworm preventives (Heartgard Plus, Interceptor Plus) and flea/tick treatments (NexGard, Simparica Trio) are priced by weight, and giant-breed doses are the most expensive tier.
• Veterinary care: $800–$2,000/year for routine care. Giant breeds often require higher doses of sedatives for procedures, which increases costs. Joint supplements (Dasuquin Advanced for Large Dogs, approximately $50–$70 for a 60-count bottle) are commonly recommended.
• Pet insurance: $80–$150/month for giant breeds. Companies like Trupanion, Healthy Paws, and Fetch by The Dodo cover giant breeds, but premiums reflect the higher veterinary costs. Consider enrolling as a puppy before any conditions are documented as pre-existing.
• Emergency fund: Set aside $3,000–$5,000 minimum. A GDV surgery alone costs $3,000–$7,000. Orthopedic surgery (TPLO for cruciate ligament repair) runs $3,500–$6,000 per knee.

Who Is This Mix Best Suited For?

The St Bernard mixed with Mastiff is not a dog for everyone. Here's an honest assessment of who thrives with this crossbreed and who should consider a different option.

Ideal Owner Profile

• Experience level: Intermediate to experienced dog owners. If this is your first dog, the combination of giant size, potential guardian instincts, and health management complexity is a lot to learn simultaneously.
• Living space: A home with ground-floor access (stairs are hard on giant-breed joints), enough room for a dog that takes up an entire doorway when lying down, and a fenced yard. Apartments are technically possible if the dog gets adequate outdoor time, but the logistics of a 170-pound dog in a walk-up are challenging.
• Family composition: Generally excellent with children when properly socialized — both breeds are known for patience. However, a 150-pound puppy can accidentally knock over small children, so supervision is essential until the dog reaches maturity and impulse control.
• Time commitment: Moderate exercise needs (30–60 minutes of walking daily), but high management needs — grooming, feeding, health monitoring, and simply cleaning up after a giant dog.
• Climate: These dogs do better in cooler climates. Both parent breeds are cold-weather adapted, and a 170-pound dog with a dense coat can overheat dangerously in hot, humid conditions. Air conditioning is non-negotiable in warm regions.

This Mix May Not Be Right If You:

• Live in a small apartment without elevator access
• Are a first-time dog owner without mentorship from an experienced handler or trainer
• Cannot budget $4,000–$7,000+ annually for care
• Want a highly active running or hiking companion — these dogs are moderate-energy at best, and giant breeds should not do sustained high-impact exercise due to joint stress
• Need a hypoallergenic or low-shedding dog
• Travel frequently and need easy boarding options — giant-breed boarding is limited and expensive

Frequently Asked Questions

What two breeds make up the St Bernard mixed with Mastiff?

This designer cross combines a purebred St. Bernard (Swiss Alpine rescue dog) with a purebred English Mastiff (British guardian breed). Both are members of the AKC Working Group and rank among the largest dog breeds in the world by weight.

How big will a St Bernard mixed with Mastiff get?

Adult males typically weigh 140–230+ lb (64–104+ kg) and stand 27–32 inches at the shoulder. Females are somewhat smaller, typically 120–180 lb (54–82 kg). Full physical maturity isn't reached until 18–30 months of age.

What is the temperament of a St Bernard mixed with Mastiff?

Most individuals are calm, gentle, deeply loyal to their families, and moderately friendly with strangers. Some may inherit stronger guardian instincts from the Mastiff side, making early socialization essential. Both breeds are known for patience with children, but the sheer size of this dog means supervision around small kids is important.

Is the St Bernard mixed with Mastiff hypoallergenic or low-shedding?

No. Neither parent breed is hypoallergenic, and this mix will shed moderately to heavily year-round, with increased shedding during seasonal changes in spring and fall. Regular brushing is required regardless of coat type.

What health issues might this mix inherit?

The primary concerns shared by both parent breeds include hip dysplasia, elbow dysplasia, gastric dilatation-volvulus (bloat), dilated cardiomyopathy, osteosarcoma, and eyelid abnormalities (entropion/ectropion). Hybrid vigor does not protect against conditions that both parent breeds are predisposed to. Always purchase from a breeder who health-tests both parent dogs.

How much does a St Bernard mixed with Mastiff cost?

From a responsible breeder with health-tested parents, expect to pay $1,500–$3,500 for a puppy. Annual care costs (food, preventives, veterinary care, insurance) typically run $4,000–$7,000+ per year. Emergency veterinary care for giant breeds is especially expensive — a single GDV surgery can cost $3,000–$7,000.

Can I find a St Bernard mixed with Mastiff in a rescue?

It's uncommon but possible. Check giant breed-specific rescues like the Saint Bernard Rescue Foundation, Mastiff Club of America Rescue, and local giant breed rescue networks. Petfinder.com allows you to search by mixed breed. Adopting an adult gives you the advantage of knowing the dog's full-grown size and established temperament.

Are St Bernard mixed with Mastiff dogs good with other pets?

Generally yes, when raised together or properly introduced. Both breeds tend to have low prey drive compared to terriers or hounds. However, same-sex dog aggression can occur in Mastiff-type dogs, particularly as they reach social maturity around 2–3 years of age. Introduce new pets gradually and consult a certified positive-reinforcement trainer if you notice tension.