Hip dysplasia is a complex disease primarily involving genetic conformation of the hip joint. Growth rate, especially in the first 60 days of life, and the mineral composition of the diet fed during puppyhood also play a large role.
Laxity or ‘looseness' in the joint ligaments is a feature of the disease and, because the joint is unstable, the head of the femur hits the acetabulum (the pelvic part of the hip joint) each time weight is put on the limb causing damage and pain. As the joint tries to stabilise itself it puts down more bone and arthritis develops.
Pain from the arthritis is variable and can be mild, such as a reluctance to jump or to negotiate stairs, through to severe and crippling lameness. Options for treatment include long-term pain relief medications, corrective surgery to improve the depth of the joint (suitable only in young dogs with only early osteoarthritic changes) and even full hip replacement - all of which have their various pros and cons and attached price tag!
A study of working dogs conducted by Paul Hughes at Taihape Vets found that 24% of Huntaways were affected with some degree of hip dysplasia, compared to only 6% of heading dogs. The dogs for the study were selected randomly and none were showing any signs of hind limb lameness at the time. He thought it likely that since working dogs are typically fit, well-muscled and highly motivated, signs of lameness aren't seen until arthritis associated with the disease is well advanced. Only the most severe cases are likely to be diagnosed early, this being before they have already been bred from. This means without x-raying every dog prior to breeding, the trait is likely to persist in the population.
Because only part of the disease is controlled by genetics, there is no 100% guarantee that breeding dogs with radiographically good hips won't have any affected pups. However, the risk is very much reduced. Keeping pups lean and feeding a balanced large breed puppy diet will also help.
If you have concerns about your dog and/or if you are considering breeding talk to your vet first - we are happy to help - we can share information, help to manage pain, or assess breeding lines by x-raying both dog and bitch prior to breeding.