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What is a blue merle or red merle coat in dogs?

The term merle designates a coat of a particular color in dogs. Although it is aesthetic, it indicates that the dog is a carrier of a gene that is not without health problems. What does it mean if the coat is blue merle or red merle? Does a dog carrying this particular gene systematically have a merle coat? Let's take a look at it.

Merle coat in dogs: a gene involved

Eumelanin and pheomelanin are the two components of melanin in dogs and genes act on these pigments. In merle dogs, due to a variation on chromosome 10, eumelanin is only distributed in certain areas. We talk about the M allele (for merle) which causes health problems in the dog, and the m allele (for "non merle"). The cause of the merle color is therefore genetic.

This particularity is apparent as soon as a puppy is born. If he is born merle, it is because he necessarily has a merle parent. A single M allele is enough to obtain a merle coat in the offspring since it is responsible for the dilution of the base color which can only be black or red. Thus, we obtain :
  • Either a dog with a blue merle coat,
  • Or a dog with a red merle coat.
There are also dogs with a cryptic merle coat commonly called ghost merle coat dogs. They can very well have only one discolored spot, hence the nickname of hidden coat.

A merle dog (whether cryptic or not) carries the mMc or McMc genotype, while the genotype of a non merle dog is mm.

Physical characteristics of a merle coat (blue or red)

In a merle coat, patches of diluted pigments are mixed with a dominant hue.

The blue merle coat: dominant gray hue with black spots. It may or may not be punctuated with white or tan markings. The blue merle coat offers a multitude of possible shades. The blue is in fact made up of black and white hairs in variable proportion, which gives a more or less clear aspect, and the dress is punctuated with splashes, patches or black flecks.

The red merle coat: dominantly beige with brown spots. White and tan markings may appear, but this is not systematic. The background of the coat is more or less dark since white hairs are mixed with brown hairs of varying intensity from one dog to another. Irregular brown spots punctuate the basic color.

Merle dogs (blue or red) have for the vast majority of them minnow eyes or blue eyes.

Marriage between two merle dogs : forbidden by the SCC

The marriage between two merle dogs leads to double merle puppies with, in addition, invasive white, which considerably increases the risks :
  • Heart disease,
  • Of blindness,
  • Deafness.
This invasive white can also be seen in dogs that do not have a merle coat since the genes involved in the coding of the white are not related to the merle. But the problems to be expected are identical. So-called "invasive white" dogs are not confirmed and therefore do not receive a pedigree. They should not be bred either since they do not conform to the breed standards.

In the same way as for the invasive white, a puppy born from two merle parents presents a dysfunction of the central nervous system. That's why he may be blind or deaf.

Note that the Société Centrale Canine (SCC) prohibits "merle x merle" marriages namely B. merle x B. merle, B. merle x R. merle, R. merle x R. merle and this, since July 11, 2017. Only the marriage between a red tri or blue tri (of mm genotype) and a blue merle or red merle is allowed.

Merle dress: the breeds of dogs concerned

Different dog breeds are affected by this genetic issue.
  • Border Collie,
  • Collie,
  • Australian Shepherd,
  • Corgi,
  • Beauceron,
  • Dachshund,
  • Shetland Shepherd,
  • Pyrenean Shepherd,
  • Chihuahua.
Adopting an animal is a long-term commitment. Before welcoming a dog with a merle coat, you should not decide only on aesthetic criteria. You have to be sure that you will be able to deal with the problems that this may entail in terms of animal health and budget for the owner, as veterinary procedures are becoming more and more expensive.