Genetics is part of the puzzle when it comes to canine health testing prior to breeding. Testing both parents is a must in order to produce the healthiest puppies possible. There are genotype (DNA tests) for certain diseases and also phenotype (physical examinations) for others that make up the whole health testing protocol. One of the most common physical screening exams is for hip dysplasia. It is a complex polygenic disease with no genetic test. Hip dysplasia is one of the phenotypical evaluations that are registrable with the Orthopedic Foundation for Animals (OFA). Embark currently tests for 250+ genetic health conditions. Many of them are also registrable with the OFA. Let’s dive into canine hip dysplasia.
Conducting a physical hip evaluation is the only way to screen dogs prior to breeding. Canine hip dysplasia can be caused by abnormal development of the hip joint or damage to the cartilage from a fracture. As the dog ages, an instability of the hip joint — a loose fit of the femoral head (ball) in the acetabulum (socket) — develops. This is called laxity. With long-term use, the ball and the socket degrades, which causes pain to the dog. The causes of hip dysplasia are complex, and can include genetics, environment, rapid weight gain from too much food, exercise, and trauma. It is more common in larger dogs. Dogs exhibit symptoms differently. Some with severe hip dysplasia may exhibit no symptoms, while others with a milder case can show lameness and limb problems.
Dogs are tested via radiograph (x-ray). It is recommended that veterinarians taking these x-rays follow the American Veterinary Medical Association guidelines for positioning a dog. Dogs must be placed on their backs in dorsal recumbency with their rear legs extended and parallel. The knees are rotated internally, and the pelvis is symmetric. Anesthesia is recommended to achieve proper relaxation. Pregnant females, or those in estrus, should not be x-rayed because hormonal fluctuations may affect the laxity of the hip joint. Once the dog’s x-ray is properly identified, along with the OFA application, it is sent to OFA for evaluation by a panel of board-certified radiologists.
Dogs must be 24-months-old to receive a permanent hip evaluation from OFA. Dogs from between 4-months to 23-months-old can have preliminary evaluations sent to the OFA.
After review by OFA, hips are classified into normal, (excellent, good, fair), borderline, and dysplastic (mild, moderate, severe) categories to rate the results of canine hip dysplasia.
Excellent is the highest rating showing a well-formed ball and socket with very little joint space between them. Good hips are less than the best, but still show a well-fitting ball and socket with good coverage. Fair begins to show a wider hip joint with a ball that can slip out of its socket. These three ratings are considered normal and OFA will issue registration numbers for them.
Borderline falls between normal and dysplastic because there are more inconsistencies present, but the arthritic changes that define hip dysplasia are not present. Failing results start with mild, with significant subluxation, and a ball partially out of the socket. While moderate dysplastic hips have a very shallow socket where the ball barely rests and the joint begins to show arthritic changes. A dog with severe hip dysplasia has evidence of the ball almost completely out of a very shallow socket, and secondary arthritic changes including remodeling, bone spurs, and other changes.
The Orthopedic Foundation of America is a leading canine health registry and public database. For more information on genetic health testing, Embark offers a search tool which lists all 250+ genetic health tests Embark offers.