A merle pit bull is actually an American pit bull terrier bred with a Catahoula leopard dog. These dogs have solid or piebald base coats with mottled patches of red, brindle or blue spots. They may also have blue or odd-colored eyes. Dogs with a merle pattern should be bred with a dog of solid color, as breeding two merle dogs can cause severe health issues to their offspring.
Often incorrectly referred to as a color, merle is a pattern in a dog's coat. It is a typical distinguishing feature of some dog breeds, such as the Australian shepherd, Shetland sheepdog and various breeds of collies. There is no purebred American pit bull with a merle pattern, and the American Kennel Club deems the pattern a disqualifying trait among pit bulls. Merle pit bulls are not considered as a purebred pit bull but more of a Catahoula dog from which the American pit bull terrier was bred.
The American Dog Breeders Association found that dogs with this pattern and color often exhibit a genetic flaw. Moreover, a dog with two copies of merle genes is more likely to be born deaf. The ADBA also states that APBT dogs with this genetic flaw could not perform their genetic task without a handicap.