Merles are the newest trend to hit Chihuahuas with devastating consequences. The coat pattern has only shown up in the breed in the past 20 years or so, and has been introduced by cross-breeding. The merle coat has also started showing up in several other breeds such as French Bulldongs, Poodles, Cocker Spaniels, and Miniature Pinschers, to name a few. Merles come in a variety of patterns, including red and blue.
The merle coloring does not occur naturally in Chihuahua DNA, but the gene is dominant so one of the parents MUST be a merle for the gene to be expressed. This is not a recessive gene that suddenly pops up unexpectedly. The only it way it got into the gene pool was by cross breeding a Chihuahua with another breed and then falsifying the pedigree dog registration, somewhere back down the line.
The problem of merles is so bad that effective March 2009, The Kennel Club (England) General Committee banned registration of any progeny produced by merle colored Chihuahuas. They are seeking to eliminate the merle gene by forbidding the breeding of any dogs of that color. No puppies will be Kennel Club registered from a mating of merle sire or dam. If European, Australian and New Zealand breeders are careful not to use American bloodlines, it is hoped the merle gene can eventually be eradicated from these breeds, thus removing the awful health problems associated with the merle coloration.
A merle Chihuahua cannot be legally papered in New Zealand with Dogs NZ. As the gene does not occur naturally in the breed, a "merle" Chihuahua, by definition, cannot be anything but a crossbreed, no matter what the breeder claims about it being "purebred". If the dog is "papered" the breeder might be using a private organisation like The Master Dog Breeders Association, which is one of several profit-making websites worldwide, set up for the sole purpose of making crossbreeds look legit by providing "papers" they print themselves.
Because the merle gene comes from much larger dogs, the chances are you will get a very "large" Chihuahuas as a result of the mixed breed dog that was introduced years ago to get the merle coloring. And the chances are high that it might be deaf, blind or both, if not when you buy it, then at some time in the future.
But even if the dog is simply large and pretty, a much more serious and important issue is the much higher occurrence of health problems in merle Chihuahuas.
The problem comes from how the merle gene works to produce the color. It does this by acting on other genes which it lightens and whitens and the whitening is what causes the defects. When a dog's coat is whitened, the pigment inside the ear and eye also whitens, making the dog DEAF and BLIND as the nerves endings atrophy and die.
According to Idexx, makers if the merle genetic blood test, "Health Problems Associated with the Merle Allele - Both heterozygous merle (Mm) and homozygous double merle (MM) dogs may exhibit auditory and ophthalmic abnormalities including mild to severe deafness, increased intra ocular pressure, ametropia, microphthalmia and colobomas. The double merle genotype may also be associated with abnormalities of skeletal, cardiac and reproductive systems."
Heterozygous mean one parent is a merle, the other is a non-merle. Also known as single merles, or Mm. Homozygous means both parents are merle, also known as double merles, or MM.
Based on information about the merle gene in Dachshunds, merles with one merle parent and the other that is a non-merle have a 36.8% chance of developing some sort of hearing loss. Other problems such as eye problems were also apparent.
A merle breeder may admit that there are problems when breeding two merles together, they often don't tell potential owners about the problems when breeding a merle to a non-merle, which is the what most merle breeders do.
You can (and do) get deaf and blind puppies from this type of breeding. If you are determined to have a merle Chihuahua, accept the fact that you may not get a healthy dog, despite how cute and healthy it seems on delivery. . A puppy with impaired hearing or vision can appear to be fine. The problems may not become apparent for months.
Merle has been popularized as a rare “designer” color by unscrupulous breeders who are more concerned with money than health. Some breeders have actually doubled-up on the color, breeding two merles together to strengthen the merle color. This practice has proved disastrous, producing Chihuahuas with life-long, and expensive to treat health defects such as blindness, deafness, or gruesome deformities as described in this article on merle color genetics by Gloria Lambert.
We do not breed merle's at Kitaco and DNA test or dogs to ensure they are free of the merle gene.