Aussie Genetics Fact Sheet: Canine Hip Dysplasia (CHD)
by C.A. Sharp
There is ample scientific evidence establishing that canine hip dysplasia is a polygenic (many genes involved) disorder which is to some degree environmentally influenced. "Environmental influence" does not mean that by keeping puppies lean and not exercising them you can make what would, under average conditions, be a severe dysplastic into an OFA excellent. It means you can tip the scales a little one way or the other.
Some CHD-affected dogs will show little or no signs of lameness while others will be so severely crippled by the disease that only expensive orthopedic surgery can relieve the condition.
Dysplastic pups can be produced from several generations of clear individuals because the disease is so complex genetically. Until the right combination of genes falls together, you don't get CHD. Looking at hip clearances on the ancestors isn't enough. You also need to know their breeding history--did they ever produce CHD? Were their siblings or other near relatives affected? If so, it indicates that they probably carry a higher "load" of CHD genes, regardless their ratings.
Accurate history can be hard to come by. The major registries (OFA and PennHIP) are "closed" and won't reveal information on affected dogs. Breeders are sometimes less than forthcoming. To make the matter even more difficult to track, only those individuals actually used for breeding are likely to be screened for CHD. A breeder could easily remain unaware of offspring that actually were affected. Not every dog with CHD requires major medical intervention, so owners may not become aware their dog is affected.
All Australian Shepherds used for breeding should have their hips screened by OFA or PennHIP. No CHD-affected dog should be used for breeding. Any dog, no matter what its rating, which produces multiple affected offspring, especially from different and unrelated mates, should no longer be bred.