Blue dog breeds
GeneticsThe dog's coat color is determined by a substance called melanin. There are two distinct types of melanin in the dog, eumelanin and phaeomelanin. Eumelanin will, in the absence of other modifying genes, give the color black or dark brown. Phaeomelanin is, in its unmodified form, red/yellow. In some dogs the coat color dilution can be accompanied by hair loss and recurrent skin inflammation, the so called color dilution alopecia (CDA) or black hair follicular dysplasia (BHFD).
Dogs with coat color dilution show a characteristic pigmentation phenotype. The coat colors are lighter in shade, diluted black (eumelanin dilution) giving a silvery grey (blue) and red/yellow giving a cream color (Isabella fawn, also referred to as lilac in some breeds). Note that dark phaeomelanin can ressemble lighter forms of eumelanin and both dark phaeomelanin and brown eumelanin are likely to be considered 'red' by many breeders, which only adds to the confusion.
In some dog breeds the blue color variety is associated with a specific coat texture. That is the case for example in the Thai ridgeback, where the blue color is almost always associated with a velvet coat texture, while the other colored Thai ridgebacks are can have either a short, a velvet or a long coat.
Blue dilution can sometimes be associated with health issues. An affection called CDA (Color Dilution Alopecia), formerly known as Blue Balding Syndrome or Blue Doberman Syndrome, causes the melanin in the hairshaft to clump together making the hair weak and breakable. Despite its former name this affection is not limited to Dobermans, but can occur in many breeds, most notable are blue Chow Chows, Dachshunds, Whippets, Standard Poodles, and Great Danes. Though fawn (dilute brown) dogs also tend to suffer from the same affection, CDA seems less common in fawns than in blues. Dilute coats also tend to be sparser in general than non-dilutes, with fewer hairs to the inch. In collies there is another type of dilution ("Grey collie syndrome") causing acyclic neutropenia, a disorder of the immune system, which renders them defenseless against infection. Puppies with this affection die within a few weeks unless kept on stringent regimens of antibiotics their whole lives.Further reading: