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The North American Mastiff: History, Characteristics, and Care - PawSafe

The North American Mastiff: History, Characteristics, and Care

Photo of Tamsin De La Harpe

Written by Tamsin De La Harpe

The North American Mastiff

The North American Mastiff (NAM) is a large emerging breed of dog that originated in the United States. These dogs are known for their massive size and gentle nature, making them popular family pets. They are also commonly used as therapy dogs due to their calm and affectionate demeanor.

Despite their intimidating size, North American Mastiffs are known for being gentle giants. Their massive sizes call for extra food, space, and joint supplements, but their loving personalities make it worthwhile.

These loyal and affectionate pups form strong bonds with their owners. However, creating a new breed is also controversial, and North American Mastiff Breeders face heavy criticism. We go through everything you need to know about the NAM and caring for mastiffs before you search for North American Mastiff puppies for sale.

This dog is bred to be an all-purpose, versatile mastiff that can adapt to most homes. The idea is to have a scary dog that is a strong deterrent for intruders but does not have the demands that come with working dog breeds. They should also have a mellower temperament than extremely dominant and powerful breeds like the Cane Corso.

Major kennel clubs like the American Kennel Club do not recognize the North American Mastiff. Still, some smaller organizations recognize it along with other massive designer mixes, including the XXL American Bully, Aussie Mountain Doodles, and Bernedoodles. These clubs include the Continental Kennel Club (CKC) and DRA (Dog Registry of America).

Some people may refer to this dog as a mixed breed dog since AKC does not recognize it. However, we’ll consider this an emerging breed. Remember that all dog breeds have to start as unrecognized mixed breeds until they become standardized and popular enough for the bigger kennel clubs to recognize them.

This breed is known for its loyalty and protective nature. They make excellent guard dogs and are great with children when properly trained and socialized. They are also known for their calm and gentle demeanor.

Origins of the North American Mastiff

Origins of the North American Mastiff

The North American Mastiff (NAM) or DeBoar X is a dog breed that originates in the United States. The breed began with Percy Dailey and Desiree Coleman from Missouri, USA, in their Monsterpiece Kennel with the aim of breeding a new kind of Mastiff.

Whenever a breeder attempts to create a new breed, they tend to face a variety of obstacles. Establishing a uniform dog that adheres to a specific breed standard takes many generations. One usually needs many breeders passionate about the project for the new breed to become viable.

Breeders trying to establish new breeds can also face heavy criticism over the issue of producing crossbred dogs that may add to the dog shelter population. Creating a new dog breed is no easy task and is almost always controversial.

It’s no different for the North American Mastiff breeders, who have faced conflict within their breeder’s society over their standards for ethical breeding and which dogs could be bred.

One of the early problems with the NAM was issues around color genetics, as many dogs were bred to be merles, and some breeders were breeding merles together to create double merle puppies that could fetch higher prices. Studies show that double merles (and breeding for color in general) can lead to far more health problems in dogs.

But the main question is, what breeds created the North American Mastiff? Desiree from Monster Kennels says they used seven foundational mastiff breeds, but she does not confirm what the seven breeds are. From what we can gather, some of the mastiffs that most likely went into the NAM are:

  • Great Danes; 
  • Cani Corsi (possibly); and 
  • and Neopolitan Mastiffs.

Owners who DNA tested their North American Mastiffs found genes that pointed to Dogue de Bordeaux, the American bulldog, and the XL American Bully in the genetics. There may also be Boerboel, Bullmastiff, or Rottweiler in the NAM.

Desiree Coleman explains the American Mastiff breeding process and provide more information in this video.

The main aim of the North American Mastiff is to have a mellower and easy-to-handle large mastiff suitable for families that can also function as a guardian. Today, around 16 kennels in the USA are working on producing the NAM and about five abroad.

Other names of the North American Mastiff include:

  • American Mastiff;
  • NAM Mastiff; and
  • De Boar X.

Recent Developments

The North American Mastiff has recently gained traction as a family pet and guard dog. The breed is known for its loyalty, intelligence, and protective instincts, all well-known Mastiff qualities.

The North American Mastiff is still a scarce breed, and there are only a handful of breeders in the United States who specialize in its breeding and development. Currently, Monsterpiece Kennel in the US and Titus Kennel in the UK are the most well-known breeders for North American Mastiff puppies for sale. 

Breeders are working to establish a standard for the breed, and there is an ongoing debate about what traits should be emphasized in breeding programs. Clubs that acknowledge the breed include: 

  • AMBC (American Mastiff Breeders Council);
  • BBC (Backwoods Bulldog Club);
  • CKC (Continental Kennel Club); and 
  • DRA ( Dog Registry of America). 

There appears to be a lot of emphasis on breeding the NAM for rare colors. Ethical breeding is always a difficult and nuanced topic. Often, dogs are bred for specific jobs, such as seeing eye dogs or service dogs, and in those cases, the dogs need to be bred with specific genetics. However, we always need to be careful when breeders emphasize aspects like color in a dog. This can be a warning sign that health and temperament are overlooked. We encourage pet owners to always look into adoption before buying puppies.

Physical Characteristics of The NAM or De Boar X

What Does a North American Mastiff Look Like?

What Does a North American Mastiff Look Like?

North American Mastiffs have the typical Mastiff look with their massive, blocky heads and extremely powerful and muscular build. They have a deep chest and a broad, strong body. They often have a thick and strong neck.

Their ears are naturally droopy, even though many people crop them (not necessary) for a more imposing look. Their muzzles are slightly shortened, and they have heavy flews (upper lips) that can make them overheat quickly, leading to much drooling. They can also be quite wrinkled and need to have their wrinkles cleaned daily to avoid skin infections. 

Color and Coat

The coat of the North American Mastiff is short and dense, with a glossy appearance. The breed comes in a variety of colors, including:

  • Blue;
  • Tawny;
  • Chocolate;
  • Black;
  • Fawn; and
  • Buckskin.

Their coat also comes in the following patterns:

  • Brindle;
  • Merle;
  • Harlequin merle; and
  • Piebald.

 Some dogs may have a black mask on their face or white markings on their chest or feet.

How Big Does a North American Mastiff Get?

The North American Mastiff is a large breed of dog known for its massive size and muscular build. Males typically stand between 24-30 inches (60-76 cm) tall at the shoulder and weigh 54 – 81 kg (120 -180 lbs). Females are slightly smaller, weighing between 120 and 180 pounds, 40-68 kg (90 -150 lbs).

Temperament and Behavior of A North American Mastiff

How Does an American Mastiff Behave?

North American Mastiffs are known to be calm, gentle, affectionate, loyal, and smart. They are loving and devoted to their owners, making them excellent family pets. These dogs should be neither shy nor aggressive but have a steady sense of self-assurance.

The NAM is a heavy dog that will sleep most of the day. They are not working dogs, so they do not have the high working drive and domineering personality of the Cane Corso, a dog they are commonly mistaken for. Ideally, the North American Mastiff should have a more even temperament that is less easily triggered into aggression.

On the other hand, they are not as huge and heavy as the English and Neapolitan Mastiffs, meaning they are a bit more athletic and alert. The NAM should be so large that the dog can’t function or so small that they lose the impressive presence mastiffs are known for.

They love being around their humans, sometimes nearly to the point of clinginess. This neediness can quickly develop into separation anxiety if not addressed. They are independent thinkers and can make decisions for themselves about potential threats.

They can have a strong prey drive and may chase small animals, so it is essential to socialize them from a young age to avoid any unwanted behaviors.

Are North American Mastiffs Good With Kids?

American Mastiffs do love children and can make good companions for families. However, they are large dogs and can accidentally knock over and seriously injure small children by accident. They should, therefore, never be around kids without supervision. Responsible ownership is key with any breed, especially one with the strength of a mastiff. This includes teaching children and dogs to interact respectfully with one another and managing environments so that small children don’t play with a dog’s food or do other things that could lead to conflict.

Are North American Mastiffs Good With Other Animals

North American Mastiffs can be friendly towards other dogs and animals if they are adequately socialized. However, they may have a strong prey drive and more stamina than larger Mastiff breeds to chase down other animals.

They can also be dominant and may not get along with other dogs, especially of the same gender and size. It is important to supervise them when interacting with other animals to prevent any aggressive behavior. You can read our blog on how to discipline a dog after fighting if your American Mastiff has any aggression toward other dogs.

Are North American Mastiffs Aggressive?

The North American Mastiff is bred to be a family companion that is easy to handle, and it should not be aggressive. That said, we must remember that this is a new breed, so we need to remember who the parent breeds are. The Neapolitan Mastiff is one of the main parent breeds, with many NAMs showing a lot of similarity to the Mastino, only in a greater variety of colors.

The NAM has the same vigorous defense drive that the Neapolitan Mastiff has. And we must also note that this is a powerful breed that shares genetics with other powerful breeds. It’s essential to respect any breed of this size and to invest in early training and socialization to avoid any problems with aggression later in life. Always be a responsible owner with dogs of this size. Regardless of how friendly or loving your dog is, ensure they are never in a position that could result in tragedy.

Health and Lifespan

Common Health Issues

The Foundation Kennel, Monsterpiece, stresses that they test their foundation stock for diseases like dysplasia and degenerative myelopathy (DM). As an emerging breed, it’s still impossible to know whether there are any breed-specific health issues. However, we can turn to what Dr. Alex Gough identifies as health issues common in mastiff breeds:

  • Hip dysplasia is when the hip doesn’t fully cover the socket. The condition is arguably the most significant risk in large dogs like AM Mastiffs. A study of 36000 dog radiographs found that Mastiff-type dogs ranked among the highest in dysplasia prevalence. Monsterpiece Kennel does emphasize that they test their dogs for hip dysplasia. However, it’s still very possible that these dogs may suffer some kind of joint issues in their lifetime.
  • Bloat or Gastric Dilation and Volvulus (GDV), where the stomach twists and fills with gas, affecting circulation. As a large breed with a massive chest, American Mastiffs have an increased GDV risk.
  • Heart issues like Dilated Cardiomyopathy (DCM), where the heart is enlarged.
  • Eye problems like cataracts and cherry eye
  • Cancer like osteosarcoma, lymphoma, hemangiosarcoma, and Mast Cells tumors are most common in mastiffs. A study on Mastiff breeds found that cancer accounted for about 47% of all deaths.
  • Common health issues like skin infections, obesity, dental problems, allergies, ear infections, and stomach sensitivity

It’s important to schedule regular vet check-ups and keep up with their vaccinations to ensure your North American Mastiff stays healthy. Additionally, feeding your dog a healthy diet and regular exercise can help prevent some health issues.

How long does the North American Mastiff live?

Since the North American Mastiff is still a new breed, the average lifespan is unclear. They live about as long as most mastiffs their size, typically 7 to 10 years.

Care and Maintenance

What Should an American Mastiff Eat?

North American Mastiffs are large-to-giant dogs requiring a nutrient-rich diet to maintain health. Feeding them high-quality dog food that contains a balanced amount of abundant protein (25 to 30%), fat, carbohydrates, vitamins, and minerals is recommended.

It’s essential to keep these dogs on a low-calorie diet and restrict their eating, especially when growing. Veterinary sources confirm that excess weight and calories for giant breed puppies lead to far more joint issues as they grow older.

The food given to the dog should be based on weight, age, and activity level. Overfeeding can lead to obesity, which can cause health problems such as joint pain and heart disease. Additionally, break apart their food into two meals to reduce GDV risk.

Exercise & Housing Needs

The North American Mastiff needs a fair amount of space to live, as they are very big dogs. They are attached to their families, and they do need to live inside if they are to be effective home guardians. These dogs do not like change, and they need a stable household with a family that is home most of the time. They do not like to move homes.

Because of their size, all exercises should be low-impact. One or two 30-minute walks per day are fine for a dog of this size. Swimming or hydrotherapy is also a great, low-impact activity for the North American Mastiff. They must stay active to maintain their health and weight, but they should never do high-impact activities like running or jumping because it places too much wear and tear on their joints.


North American Mastiffs have a short, smooth coat that is easy to maintain. They shed moderately throughout the year and require regular grooming to keep their coat healthy and shiny.


It is recommended to brush their coat once a week to remove loose hair and dirt and improve circulation in their skin while spreading natural oils through the coat to keep it glossy.


They should also be bathed monthly to keep their coats clean and free of odors. Opt for a gentle oatmeal shampoo to keep their coats clean without risking stripping the natural coat oils. This is vital for the North American Mastiff as they can be prone to skin issues like hot spots and often have sensitive skin.

Other Grooming

Additionally, trim their nails with pet nail clippers regularly to prevent them from growing too long and causing discomfort. Also, clean their ears regularly with canine ear wipes to prevent infections.

Although American Mastiffs are less wrinkly than some Mastiffs, be sure to keep the few wrinkles they do have dry and clean from debris to avoid infection.

How to Train the North American Mastiff

Training Techniques

Training a North American Mastiff requires a firm and consistent approach. They are intelligent dogs that respond well to positive reinforcement methods.

One effective training technique is clicker training. This involves using a clicker to mark the desired behavior and then rewarding the dog with treats or praise. Another technique is leash training, which helps to establish boundaries and control the dog’s movements.

Socialization is also important for North American Mastiffs. Exposing them to different people, animals, and environments at a young age can help prevent aggression and fearfulness.

Common Challenges in Training American Mastiffs

One of the biggest challenges in training a North American Mastiff is their stubbornness. They can be independent and may not always listen to commands. It is important to remain patient and consistent in your training approach. They are soft dogs, and harsh methods will only create problem behaviors.

Another challenge is their size and strength. North American Mastiffs can weigh up to 180 pounds, so using proper training equipment, such as a sturdy leash and harness is important. They may also require additional training to prevent jumping or pulling on the leash.

Separation anxiety is another common issue with North American Mastiffs. They are loyal dogs that thrive on human companionship, so it is important to gradually acclimate them to being alone and provide plenty of mental stimulation when you are away.

Training an American Mastiff is necessary because their size and power can become dangerous otherwise. This is not to say that small dogs shouldn’t be trained, but the situation is much worse when you have an ill-trained canine that can overpower you.

Ideal Home for An American Mastiff

  1. A home with a secure yard;
  2. Non-allergic household;
  3. Experienced owners; and
  4. Adult supervision if kids are around.

Frequently Asked Questions (FAQs)

How much do North American Mastiff puppies cost?

The cost of a North American Mastiff puppy for sale can vary depending on the breeder, location, and pedigree. On average, a North American Mastiff puppy can cost anywhere from $1,500 to $3,000 or more.

Do North American Mastiffs Bark A lot?

American Mastiffs are not known for excessive barking. When they bark, they want to alert you to a stranger or other unusual activities. Training also goes a long way in reducing excessive barking.

What breeds are used to create a North American Mastiff?

Seven breeds went into creating the North American Mastiff or NAM. However, the foundation kennel, Monsterpiece, has yet to specify which breeds these are. We know that two of the seven foundation breeds are Great Danes and Neapolitan Mastiffs. Other possible influences are Bullmastiffs, Dogue de Bordeaux, Cane Corsos, American Bulldogs, Pitbulls or XXL American Bullies, and possibly other mastiffs like Rottweilers or Boerboels.

Are North American Mastiffs known for being aggressive?

No, North American Mastiffs are not known for being aggressive. They are typically calm, gentle, and loyal dogs. However, like any dog, they can become aggressive if they are not properly socialized or trained. As with any powerful breed, responsible ownership is essential.

Is the North American Mastiff a good guard dog?

Yes, North American Mastiffs can make excellent guard dogs. They are large, powerful dogs that are naturally protective of their family and home. However, they must be properly trained and socialized to be effective guard dogs. Most of these dogs work well as guardians simply as a deterrent because of their intimidating appearance. Dogs that are too aggressive with strangers may be a problem. 

Can North American Mastiffs be good family dogs?

Yes, North American Mastiffs can make great family dogs but we recommend owners that are experienced with large and powerful dogs. They are affectionate and loyal to their family members, especially children. However, due to their size and strength, they may not be suitable for families with very young children.

What is the difference between the Cane Corso and the North American Mastiff?

The Cane Corso and North American Mastiff are both large, powerful breeds. However, the North American Mastiff is an emerging breed derived from seven mastiff breeds. At the same time, the Cane Corso is a purebred Italian Mastiff. The North American Mastiff is typically larger and has a more laid-back personality, while the Cane Corso is more agile, athletic, domineering, and challenging for inexperienced owners.

Final Thoughts

The North American Mastiff is a large, powerful breed that requires an experienced and dedicated owner. This breed is known for its loyalty and protective nature, making it an excellent choice for families or individuals looking for a devoted companion.

While the North American Mastiff can be a great addition to the right home, potential owners should be aware of the breed’s potential health issues, such as hip dysplasia and bloat. Regular exercise and a healthy diet can help mitigate these issues, but it is important to work closely with a veterinarian to ensure that the dog remains healthy throughout its life.

Meet Your Experts

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Tamsin De La Harpe


Tamsin de la Harpe has nearly two decades of experience with dogs in rescue, training, and behavior modification with fearful and aggressive dogs. She has worked closely with veterinarians and various kennels, building up extensive medical knowledge and an understanding of canine health and physiology. She also spent two years in the animal sciences as a canine nutrition researcher, focusing on longevity and holistic healthcare for our four-legged companions. Tamsin currently keeps a busy homestead with an assortment of rescue dogs and three Bullmastiffs.

Tamsin de la Harpe has nearly two decades of experience with dogs in rescue, training, and behavior modification with fearful and aggressive dogs. She has worked closely with veterinarians and various kennels, building up extensive medical knowledge and an understanding of canine health and physiology. She also spent two years in the animal sciences as a canine nutrition researcher, focusing on longevity and holistic healthcare for our four-legged companions. Tamsin currently keeps a busy homestead with an assortment of rescue dogs and three Bullmastiffs.