Double Merle is a term used to describe dogs that inherit two copies of the merle gene, resulting in a unique but often problematic coat pattern.
The merle coat pattern is sometimes referred to as a colour, but in reality, the colouration is due to a gene that alters the way pigment appears in the coat. The genetic combination can lead to serious health issues.
What is the merle gene?
The dominant merle gene causes certain pigment cells to be diluted, resulting in a mottled coat, with lighter and darker patches. Dogs may also have two blue eyes, or one blue and one brown eye.
Unfortunately, this same gene also carries hidden risks. And while dogs carrying just one copy of the merle gene do not typically face significant health problems, when two merles are bred together, they produce what is known as a homozygous merle puppy. The double dose of the gene significantly raises the likelihood of severe health complications.
Which breeds can have merle coats?
"Merle" is recognised as an acceptable coat pattern in breeds such as the Border Collie, the Australian Shepherd, the Chihuahua, the Dachshund and the Great Dane.
What is a double merle dog?
Double Merle dogs usually have a predominantly white coat, but not every white puppy is a double merle. Other genetic combinations can also result in a white puppy.
When two merle-patterned dogs are bred together, each of their puppies will have a 25% chance of inheriting the gene.
What are the health issues for a double merle dog?
Double Merle dogs may suffer sensory impairments and are at higher risk of suffering from congenital deafness and blindness. This is because the absence of pigmentation results in defects in the structures needed for vision and hearing.
Double Merle dogs are sometimes referred to as "lethal whites".
The suggestion that the condition may be fatal is inaccurate, but the potential health issues can seriously impact the dog's lifestyle and wellbeing.
Genetic complications can also arise within the immune system, with some Double Merle dogs more prone to allergies, skin issues and autoimmune diseases.
What is life like with a double merle dog?
Puppies found to be born deaf or blind commonly end up in the rescue system, as breeders are unable to sell them on. But despite challenging health concerns, many double merles go on to lead joyful, active and happy lives.
With positive reinforcement training and careful supervision from their owners, they learn to adapt to their surroundings despite the vulnerabilities caused by their breeding.
Responsible breeding practices
Merle to merle breeding is currently banned by the UK Kennel Club, and the practice of intentionally breeding two merle dogs together is highly controversial.
Litters should be carefully planned, with breeding programmes carefully implemented to prevent the birth of homozygous merle puppies. Breeders should be aware of the risks of breeding two merles, taking steps to prevent the creation of a merle-to-merle litter.
