Yorkshire terriers, commonly called Yorkies, have maintained a spot on the American Kennels Club's most-popular-breeds list for years. Their popularity, as is inevitable with popular purebred dogs, fosters over-breeding that can perpetuate a genetic mutation that causes a skeletal deformation called parrot mouth. Not all Yorkies have this gene.
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Originating in England, Yorkshire terriers were developed for catching and killing the various rodents infesting mines and mills. Yorkshire terriers of the late 1800s were larger than they are today, many weighing in at 10 pounds. In an effort to create a smaller, more companionable dog, Yorkie enthusiasts blended four distinct terriers to produce the Waterside terrier. English royalty took an interest in the newly developed lap dog, breeding interests were moved to the Northern England county of Yorkshire and the dog was renamed.
Uncertain as to how the gene for canine malocclusion was introduced into the Yorkie line, experts agree most cases have a hereditary link. The website for the Tri-County Animal Hospital of Wayne New Jersey lists selective breeding, based on preferred breed characteristics, and early detection as means to avoid this deformation.
Scissor Bite and Malocclusion
A perfect bite conformation is referred to as a scissor bite. This normal occlusion exists when the teeth of the dog's upper jaw rest in line with the teeth of the lower jaw. For a Yorkie's bite to meet breed standard, the upper incisors must rest just in front of the lower incisor when the dog's mouth is closed. Malocclusion is the developmental deformity defined as an incorrect bite. This particular form of malocclusion is called brachygnathism, or parrot mouth. Parrot mouth is often called "overshot" jaw among breeders and handlers.
Parrot mouth can be detected in puppies as early as three weeks, but the full extent of the condition will not be evident at this point. Parrot mouth is a growth abnormality that will continue until the dog's jaw stops growing. This form of canine malocclusion can lead other serious health issues. Difficulty chewing and swallowing is evident in all dogs with a brachygnathia issue; it can develop into digestion difficulties. Parrot mouth can cause severe tooth erosion, contributing to gum disease and dental decay. Mouth sores and drooling may be symptoms of parrot mouth malocclusion. According to a Sydney University veterinary case study, orthodontics can correct mouth abnormalities, but heredity dictates the gene will continue to affect future litters.
While it is uncertain where this malformation began, veterinarians have made a direct genetic connection. The staff at Tri-County Veterinary Hospital list congenital, or hereditary, factors and breed predilection as the possible culprits of parrot mouth. They cite overcrowding of the teeth, diseases of the gums and tissue defects from traumatic contact as potential causes. According to Dr. Lowell Ackerman, DVM and author of "Owner's Guide to Dog Health," dogs with parrot mouth should be pulled from breeding programs and surgically castrated. Dr. Ackerman advises potential Yorkie owners to look for established, recognized organizations to find contact information for creditable breeders.
Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.