Blue merle shelties are undeniably beautiful color specimens of the Shetland Sheepdog breed. But if they are the product of breeding two dogs with the merle gene, the puppies can be prone to hearing and vision disorders. The merle factor can be difficult to determine, except by experienced breeders with knowledge and understanding of the line's pedigree.
Understanding the Gene
Shelties come in various colors: brown and white sables, black, white and tan tri-colors, black and white bi-blacks, blue merle grey, black white and tan, and several combinations of those colors. Sheltie puppy colors are dictated by their parents as you'd expect. But it's possible for one or both parents to have recessive color genes that may not show in the dog's coat. A sable sire or dam can carry the merle gene without having the color. If bred to another sheltie with the merle gene, it will produce double merle puppies. Double merles are subject to genetic disorders affecting vision and hearing.
Making Blue Merles
Blue merle shelties are produced when one parent has the merle gene. The blue merle color pattern is not blue; the dog's black pigment is diluted, making the hair appear silver or grey. The darker color usually appears as mottled spots on the dog's coat. A blue merle sheltie will have some tan points in the coat. A black, white and grey merle sheltie with no tan coloring is called a bi-blue. These colors are produced by breeding one tri-color or bi-black dog with the merle gene to another one without it.
Double Merle Problems
Geneticist Lee Anne Clark says merle-to-merle breedings may be difficult to detect, but health issues in their puppies are usually the result. Breeding two merles creates a pigment disorder, explains Clark, which affects the color and shape of eye development and inner ear nerve endings. These two issues cause light blue eyes and vision problems for the offspring of these breedings that can result in blindness and, sometimes, deafness or hearing problems. At the onset, you may notice that a growing puppy or adult dog bumps into things or isn't able to focus on you visually. Your dog may not appear to hear you when you call him, or he won't startle at noises such as hand clapping.
Identifying the Gene
If a breeder is unaware of the merle gene in a dog being used for breeding and that dog is bred to another merle, it's a recipe for creating health problems. It's impossible to assess the dog's genetic background just from the coat color. The breeder must know the pedigree to be aware of the existence of merles in the dog's lineage, or the pair must be tested for DNA to determine whether the merle gene is present. The only way to identify the merle gene is through the dogs' pedigree or DNA testing.