Published by TSK Editor on

In certain breeds of dog, there is a coat pattern known as ‘merle’. It is sometimes referred to as a color, but it’s actually the result of a gene altering the way pigment appears in a dog’s coat. The merle coat pattern has recently become more popular — due to it’s unusual pattern and look.

Since the merle coat pattern is unique to each individual dog — some breeders have used this as a marketing ploy or a sales tactic, attempting to lure unsuspecting buyers (especially those who are new to the breed) into paying higher prices thinking they’re actually purchasing ‘rare’ colored Staffords.

Unfortunately, there are several health issues associated with the merle gene mutation — and the risk of these problems occurring only increases when two merle dogs are mated together.



  • Blue Merle

Though a variety of merle colors are referred to by breeders and dog owners, the two most commonly seen types of merle are blue merles and red merles. Blue merles are, in fact, grey. They appear like a tri-color dog (black, white and tan), but with patches of the black appearing ‘faded’ or grey.

  • Red Merle

Similarly, a red merle will have faded patches of red and will often look more mottled than the blue merle. While all of the breeds with the merle coat pattern produce blue merles, only certain breeds produce red merles. The strength of the other colors in the dog’s coat (tan and black, or red and tan) can vary as well, with some merles appearing to have extremely pale coloring all over, while others can have quite strong patches of color.

Blue merles with no tan markings at all are known as bi-blues, but a red merle does not necessarily have to have tan markings.


Merles commonly have blue eyes. Sometimes they may have one blue and one brown eye. They can also, on occasion, have two brown eyes. Sometimes dogs may appear to have normal coat coloring but are in fact still merles and will produce puppies with the merle colouration.

These are known as ‘cryptic merles’, but the exact reason why such dogs do not display the merle pattern remains unknown. This is one of the main reasons that we need to consider adding a disqualification of all merle Staffords to our Standard, but any dog with merle anywhere in it’s pedigree even if they are not visibly merle (cryptic merles).

The merle gene is usually dominant, so a merle dog will have inherited the gene from one of its parents. While a non-merle dog (unless a cryptic) will have inherited no merle gene. For example, in a litter of mixed color puppies the non-merles will be (mm), while a merle will be (Mm), meaning it has inherited one merle gene and one non-merle gene.


There is scientific evidence to suggest that the merle gene can be linked to a higher rate of ocular, auditory issues in addition to skeletal, cardiac and reproductive abnormalities.

  • Occular (Eye) Issues
  • Auditory (Ear) Issues
  • Skeletal, cardiac and reproductive abnormalities

A 2006 paper on the merle gene first published by the National Academy of Sciences of the United States of America attempted to identify the gene in dogs that caused the merle pattern.

One study reported 36.8% of dogs with the merle coat pattern (Mm) suffered hearing problems ranging from mild to complete deafness. While none of the dogs in the control group of non-merles (mm) had any hearing issues.

Another found merles had “significantly greater” frequency of eye abnormalities than non-merles. Other studies have found that the merle gene is associated with skeletal, cardiac, cancers, skeletal, temperamental, neurological and reproductive abnormalities.


All merle dogs have the genotype Mm — meaning they have one allele for merle and one allele for non-merle. All non-merles are mm. If you breed a merle (Mm) to a non-merle (mm) you will on average produce a litter in which a half of the puppies get the M allele so are Mm (merle) and half get the non-merle allele so are mm.

But, if you were to breed two merles together (Mm X Mm) you will produce on average a quarter mm (non-merle), a half Mm (merle) and a quarter MM (double-merle; also called double-dapple). And the double merles don’t look like typical merles. Instead, they’re mostly white with merle patches.

The main reason you want to avoid producing MM dogs is that they often have visual and auditory problems.


A double merle is created when two merle dogs are bred together. It doesn’t matter what color merle or what breed they are. If two merle dogs are bred together, each puppy in the litter has a 25% chance of being born a double merle. A double merle inherits the merle gene twice. One copy of the merle gene causes a marbling effect on the coat and creates lighter spots throughout the solid color coat.

In a double merle, the marbling/lightening effect is doubled and the coat becomes predominantly white.

Double merles also have a very high chance of being deaf, blind, or both because they lack pigment where it would normally be.

Puppies that do not inherit the gene twice are considered “normal” dogs.

Their coats are normally marked and they are not plagued with hearing or vision problems. These are the pups that a breeder wants, because they can profit the most from these pups.


The extreme lack of pigmentation is what makes these dogs unhealthy and prone to multiple conditions. It goes along with:

  • Hearing impairment — ranging from light deficits to complete deafness
  • Vision impairment — up to complete blindness
  • Microphthalmia: a rare condition causing very small eyeballs that sometimes have to be removed
  • Skin cancer due to the lack of pigmentation and no protection from UV light


The question many ask is — if breeding merle to merle has such a high chance of producing disabled puppies, why would anyone do it? There are several answers to this question, the first being plain ignorance.

Not everyone knows the risks of purchasing a merle Staffordshire Bull Terrier or worse yet — breeding two merle dogs together. Ideally, breeders that sell merle puppies should explain the risks associated with breeding merle to merle, especially if the Customer already has a merle dog of the opposite sex.

But, as this is unlikely to happen, accidental creations of double merles will continue to occur.


As long as there are merle coated dogs, double merles will be produced — either by accident or through ignorance on the part of the breeder. However, a great deal can be done to discourage the breeding of double merles and to educate the public on the dangers.

Official bodies and Kennel Clubs can lead the forefront in discouraging the deliberate breeding of double merles, but educating puppy buyers will also help. Uneducated customers are often sold double merles as ‘rare white’ or ‘albino’ versions of a certain breed, without knowing that their pup may go deaf or blind.

Equally, pet owners with two merles may breed their dogs without realizing the consequences. Spreading the word about the dangers of breeding merle to merle is, just part of the answer.


The following breeds carry merle and are recognized by the AKC as an acceptable color:

  • Australian Shepherds
  • Pyrenean Shepherd
  • Great Danes
  • Koolies
  • Collies
  • Shetland Sheepdog
  • Catahoula Leopard Dog
  • Welsh Cardigan Corgi
  • Olde English Bulldog
  • Pomeranian
  • Poodles
  • French Bulldogs



Merle Coats are not accepted by the AKC in most dog breeds and are only accepted in breeds where the merle coat naturally occurs such as Leopard Dogs, and Border Collies. Merle does NOT exist in the Stafford, therefore if you find them it is 100% a mixed breed.

The same goes for the UKC in the United Kingdom with the exception of Poodles as the UKC stopped accepting them in 2020.


The merle gene is being introduced into new breeds everyday. Merle is now present in Poodles, Bulldogs, American Staffordshire Terriers, American Pit Bull Terriers and American & Exotic Bullies. It’s become even more prevalent in many of the newer “designer breeds.”

The overabundance of these dogs is heartbreaking. There are rescues all over the country committed solely to rescuing merle dogs — that should speak volumes by itself. One online article on merle in the breeds it currently exists in cites:

“these are 100% preventable. Don’t breed two merle dogs, and you won’t have double merles.”

I agree with that very general statement: “don’t breed merle to merle and there won’t be double merles.” True. Sounds good on paper as well.. Yes, if you don’t breed merle to merle, there won’t be any double merles — in that particular litter. And again, remember, merle DOES NOT OCCUR NATURALLY in the Stafford!

While the self appointed “ethical merle breeders” boast online about being “responsible” merle breeders — they are still contributing to serious health issues in our breed. Yet pat themselves on the backs for indirectly contributing to the problem instead of being directly responsible. Don’t fall for the gaslighting.

So why is it that unethical Staffordshire Bull Terrier breeders continue to breed merle — when it’s proven to be linked to serious health problems, issues and abnormalities and never existed without mixing in other breeds?


  • Money

Most merle breeders in the Stafford breed make the decision to purchase merle dogs or have merle litters because they heard or were told that’s “where the money’s at.” But it’s simply not true. Quality, fully health tested Staffords meeting the breed standard will always produce healthier dogs than a short term fads. Healthier dogs require fewer visits to the vet. Therefore, the cost of a PURE BRED Stafford of acceptable coat color/pattern will cost you less in the long run.

Setting health concerns aside for a second and looking at things strictly from a business perspective — merle isn’t “where the money is at.” Maybe if you were an Stafford breeder that struggled to sell pups at a decent prices— a gimmick like “rare colored” or a fad like “merle” could result in higher sales prices short term, but there’s no longevity to it.

  • “Rare” & Unique Colors

The second biggest reason that breeders choose to go the merle route is the belief that there’s higher demand for “unique and rare” colors in the Staffordshire Bull Terrier breed. This is true.. to an extent. Color is in right now, but it can be added without merle and the issues that come with it. Staffords already come in many wonderful colors, piebalds and brindles!

Breeders can add color without sacrificing structure, health, temperament — and have a breeding program with longevity — instead of cashing in on a short term fad, having a couple of litters then disappearing.


  • They Don’t Know Any Better
  • They believe they’re buying “rare” color Staffordshire Bull Terriers

My concern is for the Stafford — to help educate those who might be new to the breed or considering breeding. To the ones thinking about having a litter or breeding — do your homework. Be aware of the time and cost involved before jumping in blindly. Have a set plan and an emergency back up one in place. Understand that it’s your responsibility to place pups that you bring into the world, into good homes with responsible owners. Get yourself a good mentor. Join breed clubs, including the AKC parent club SBTCA and your local clubs.

Stop introducing new health issues that are both unnecessary and completely avoidable.


Although they’ve been popping up on social media sites and advertised as “rare colored” Staffords  — the Merle coat pattern is not rare, its a mutt. It’s the result of a gene mutation and riddled with health problems and can only occur by bringing in other breeds.

Merle is a fad, nothing more. And it’s not anything new. This is the third or fourth wave of merle becoming more popular in the Stafford breed over the past 10 years. Ask any merle breeder from the first few waves how it worked out for them — oh wait.. you can’t. Because there aren’t any of them left.

The Stafford is a wonderful, loyal and kind dog no matter the color of its coat, but when that color is bred only to suit the fancy of a small group of people it becomes both immoral and unethical. Responsible Staffordshire Bull Terrier breeders should refuse to produce these mutts and should strive to educate those who do.