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Merle Chihuahuas

    Due to the increasing popularity of this color pattern, I feel that I need to add some information about Merle Chihuahuas, including the potential health problems, on my website. Many people interested in purchasing a Merle Chihuahua, may be unaware of the problems that they might have with their new pet.

Hopefully, with more knowledge about this pattern, breeders will reconsider breeding this color pattern.

To control the pattern in the breed, these countries (and/or kennel clubs) so far have taken action:

Australia (banned registration of merles)
New Zealand (banned registration of merles)
Canada (Merle is now a Disqualifying Fault (DQ) in the Chihuahua standard)
Great Britain (Merle is now a Disqualifying Fault (DQ) in the Chihuahua standard and merles are also banned)
Germany (Merles can not be shown/bred)

Updated July 27, 2009
ALL FCI countries (83 countries) have now made merle Chihuahuas a Disqualifying Fault (DQ), and in several countries, this means puppies from merle parent(s) can not be registered.
See full list of applicable member countries here: http://www.fci.be/membres.aspx

Updated June 24, 2010
Merles are NO LONGER registerable in Canada, whether it be puppies that come from a merle parent, or merles that are imported from other countries.
Policy and Procedures Manual, Registration, section F, under Chihuahuas.

Unfortunately over the past 10-15 years since this page has been published, many of the website links below with information have been lost overtime and no longer work.
However, at this time, which has not changed in the last years, merle is still a color pattern that is a DQ or banned color registration in most of the world.
Additional links have been provided with new information and studies to date, as well.

   Merles are the newest fad to hit Chihuahuas. The coat pattern has only shown up in the breed since 1990. There is NO mention of this color what-so-ever in any Chihuahua breed book, or genetics book that lists certain color patterns that are in the Chihuahua breed. This coat pattern has also appeared simultaneously in several other breeds as well (these include Poodles, Cocker Spaniels, APBT, and Miniature Pinchers). Merles can come in a variety of color patterns, including red merle and blue merle (above). They can also have what is called a hidden or cryptic merle, where the merle pattern does not show up, such as on a light colored dog, or where the merle pattern does not cover a large area of the dog (although rare, genetically sometimes only one hair on the dogs will actually be merle patterned).

The Merle gene itself is a dominant trait, which means one of the parents MUST be a Merle for the gene to be expressed (or show up) in a puppy. This is not the type of gene that remains hidden for many generations like a recessive gene. Since Merles were never documented more then 25 years ago, this color pattern has probably unfortunately resulted from cross-breeding other breeds of dogs that have merles such as a Dachshund, to the Chihuahua, with speculation that registration papers that have not been accurately filed, so they were registered as full purebred Chihuahuas. While the Merle color can come up from genetic mutations, this is most likely not the case as it is the same gene that is also present in Aussies, Dachshunds, Shelties, etc.

 Ultimately, if you buy a Merle Chihuahua, you are probably not getting a purebred Chihuahua. Also, a large majority of Merle Chihuahuas are consistently big, in the 6 to 10 lb range, which is unlike a purebred Chihuahua and is probably a result from a throw-back to the mixed breed dog that was introduced years ago to get the Merle Chihuahua.

Further Information on the Health of Merle Chihuahuas

    Another much more serious and important issue is the higher occurrence of health problems in Merle Chihuahuas. You may wonder how this is so, when merle is only a color pattern? Well, unfortunately, unlike other colors, the merle gene acts on a color and lightens and whitens certain parts of it (creating patches)...the whitening is what causes defects. Often, when a dog's coat is whitened, the pigment inside of their ear and on their eye, also whitens...making the dog DEAF and BLIND as the nerves endings atrophy and die.

Definition of Heterozygous-one parent is a merle, the other is a non-merle. Also known as single merles, or Mm.
Definition of Homozygous-both parents are merle. Also known as double merles, or MM.

As quoted from UCDavis, makers if the merle genetic blood test (https://www.vgl.ucdavis.edu/services/dog/Merle.php):

"Blue and partially blue eyes are typically seen with merle, and merle dogs often have a wide range of auditory and ophthalmologic defects.  Dogs with 2 copies of merle (called double merle) are primarily white and can have multiple abnormalities of skeletal, cardiac and reproductive systems, thus breedings between 2 merle dogs are discouraged to avoid producing double merle offspring."

Based on information about the merle gene in Dachshunds, all merles that are brought into the world have as high of a chance as 36.8% of developing some sort of hearing loss, resulting from either slight hardness of hearing to total deafness (Dr Willis). This percent is for puppies that result from one parent that is a merle, and the other that is a non-merle. Other problems such as eye problems were also apparent. While many breeder's admit that there are problems when breeding two merles together, there is a documented risk of problems developing from single merle breedings. Unfortunately you can still get deaf and blind puppies from this type of "safe" breeding, that produces the merle coat pattern. So please keep in mind, if you are interested in getting a Merle Chihuahua, you may be getting a pup with impaired hearing or vision. For the reason of health problems and questionable parentage, the presence of the merle pattern in Chihuahuas is being banned in many countries world-wide. For more information on this study by Dr. Willis, and for his viewpoint of the merle pattern in Chihuahuas, please go here: Original Article and statistics were published by Dr Malcolm Willis in Our Dogs, "Time to Call a Halt" (2005). Link no longer valid to article, unfortunately.

Additional link and study about merle gene/allele related defects both in homozygous and heterozygous merles, this time with statistics over several different breeds by Dr Strain. http://onlinelibrary.wiley.com/doi/10.1111/j.1939-1676.2008.0257.x/full

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