Despite the fact that merle-colored cocker spaniels exist, they are not considered an authentic breed. Merle-colored dogs are bred for the novelty of their unusual color. Associations like the American Spaniel Club, Inc. believe that breeding merle colored dogs poses serious health risks and should be ceased.
Origin of Merle Gene
Merle cocker spaniels are born with a mutated merle gene, which results in a pigment discoloration in their eyes and coats. Some speculate that the merle gene was introduced through an outside breed, though it is not possible to prove this scientifically. A study done at Texas A & M, published in the National Academy of Science, suggests that the merle gene actually originates back from wolf ancestors, before dog breeds had diverged.
Health Problems of Merle Mutation
The mutation that results in the merle color in dogs is an interuption of the pigmentation gene SILV. This mutation can cause a number of health issues as it takes effect early on in the developmental stage of the dog. Breeding dogs with the merle gene can create offspring with hearing loss, a multitude of eye problems and blindness, color dilution, hair loss/baldness and other issues, such as defects in their cardiac, skeletal and reproductive systems, which can lead to death.
While not all merle cockers suffer from health issues, there is no doubt that numerous health issues can be linked specifically to the merle genetic mutation. This risk is increased when merles are bred with other merles. While breeding merles with non-merles also poses health risks, merles bred with other merles can create dogs that have a greater likelihood for suffering from vision and hearing problems. If a breeder isn't sure of the merle status of his male cocker spaniel, they should get a DNA test for the merle mutation so that they don't create more merle offspring.
Merle Breeding Strongly Discouraged
Breeders like to breed dogs for specific coloring patterns, but research shows that this behavior is unwise. Associations, like the Skyline Cocker Club and the American Spaniel Club, agree that the breeding of dogs with the merle mutation should cease due to the numerous health problems that can result. Instead, breeders should focus on breeding for factors, such as temperament, health and field ability, and not on trying to produce dogs with unusual colors.