The Bullmastiff is a large-sized breed of domestic dog, with a solid build and a short muzzle. The Bullmastiff shares the characteristics of molosser dogs, and was originally developed by 19th-century gamekeepers to guard estates. The breed's bloodlines are drawn from the English Mastiff and the extinct Old English Bulldog. It was recognized as a purebred dog by the English Kennel Club in 1924.
|Domestic dog (Canis lupus familiaris)|
Bullmastiff males should stand 25–27 inches (64–69 cm) tall (American Kennel Club (AKC) standard) at the withers and weigh 110–130 pounds (50–59 kg). Females should be 24–26 inches (61–66 cm) at the withers, and 100–120 pounds (45–54 kg). Exceeding these dimensions is discouraged by breeders.
A Bullmastiff's coat may appear in fawn, red, or brindle. These are the only acceptable colours in the AKC standard. The fawn can range from a very light brown to a reddish brown. Red can range from a light red-fawn to a dark, rich red. Brindles are a striped overlay of the fawn or red. A Bullmastiff should have no white markings, except for on the chest where a little white is allowed.
Bullmastiffs are a large working breed originating in Britain in the mid 1800s as estate guardians to ward off poachers. They were bred by gamekeepers for strength, size and speed using a cross of the tough, heavy and aggressive Bulldog of the 19th century with the large, strong, less aggressive Mastiff. As a result, the Bullmastiff is known as the Gamekeeper's Night Dog. The preferred color, by gamekeepers, was brindle, as this color works as a more effective camouflage, especially at night.
The Bullmastiff breed was deemed pure by the English Kennel Club in 1924, with a genetic background of approximately 60% Mastiff and 40% Bulldog. In 1934, the AKC recognized the Bullmastiff. The first standard for the breed was approved in 1935. The standard has undergone several revisions since then; the most current version is available on the AKC website.
Bullmastiffs are strong, powerful, but sensitive dogs. For a Bullmastiff to become a well-behaved family member, consistency is needed. Training and socialization is of high importance, as the breed can be independent. Dogs of this breed are natural guardians of their home and owners. No special guard training is needed for a Bullmastiff to react appropriately if its family is endangered. During training, a Bullmastiff requires a special approach, because these dogs do not like to repeat the same actions again and again. Activities Bullmastiffs enjoy include obedience, agility, tracking, and carting.
A UK survey based on the lifespan of 96 Bullmastiffs found a median age of 7.5 years. A Bullmastiff does not stop growing until their second birthday.
Health concerns within the breed include hip and elbow dysplasia, progressive retinal atrophy, bloat, and cancer, with a relatively high incidence of lymphoma and mast cell tumours. Bullmastiffs are prone to certain hereditary diseases, including:
- Hip dysplasia, affecting 24.5% of individuals 
- Elbow dysplasia, affecting 13.8% of individuals,
- Entropion, hypothyroidism affecting 2.8% of individuals,
- Progressive retinal atrophy is a particular problem, since the trait is an autosomal dominant one. (This has recently been called into question by another medical team and has been proven that some Bullmastiffs have autosomal recessive PRA genes. In America, this is being investigated by the American Bullmastiff Health and Research Committee, and the DNA Optigen test only works for dominant genes, so it is considered inadequate at this time.)
- Gastric dilatation volvulus, also known as bloat.
Cosmetic genetic problems include longhairs and "Dudleys". Both are recessives and not common. The Dudley, named after a notable Bulldog breeder of the 19th century, the Earl of Dudley, is a lack of pigment in the mask. It can be liver colored or simply not present.
- Bullmastiff Page
- AKC standards
- "Get to Know the Bullmastiff", 'The American Kennel Club', Retrieved 29 May 2014
- Walkey B. The Bullmastiff Fancier's Manual. Sechelt B.C., Canada: Coast Arts Publishing; 1992
- "Bullmastiff". Animal Planet. Retrieved 12 March 2015.
- "1935 Bullmastiff standard" (PDF).
- American Kennel Club — Bullmastiff
- "Breed standard (Appendix A)" (PDF). Sabt.co.za. Retrieved 2012-09-18.
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- Orthopedic Foundation for Animals. "Hip Dysplasia Statistics". Retrieved 2013-06-11.
- Orthopedic Foundation for Animals. "Elbow Dysplasia Statistics". Retrieved 2013-06-11.
- Orthopedic Foundation for Animals. "Thyroid Statistics". Retrieved 2013-06-11.
- "PRA". Swedish Bullmastiff Club.
- Shepatin, Matthew (2009). "Then Madden Said to Summerall. . .": The Best NFL Stories Ever Told. Triumph Books. p. 134. ISBN 1617491985. Retrieved August 2, 2017.