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How have hip dysplasia scores been used to reduce the disease in German shepherd dogs and Labrador retrievers?

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Red Poll cows — Animal breeding Red Poll cow and calf.

In the context of animal breeding, hip dysplasia is a complex, polygenic condition that is difficult to control because it is not associated with a single allele. To manage this, radiologists developed a scoring index that allows breeders to evaluate young dogs and assign a score indicating their likelihood of developing the disease as they age.1

By using these scores as a selection tool, breeders can make more informed decisions about which animals to include in their breeding programs. This method has proven highly effective in reducing the incidence of the disease. In a notable breeding experiment reported by geneticist E.A. Leighton in 1997, selection based on these scores resulted in significant improvements within fewer than five generations:1

German shepherd dogs: The incidence of hip dysplasia in the experimental population dropped from 55 percent to 24 percent.1
Labrador retrievers: The incidence of the disease decreased from 30 percent to 10 percent.1

These results demonstrate that even for traits with complex genetic underpinnings, objective or well-designed subjective scoring methods can significantly improve the accuracy of selection and reduce the prevalence of hereditary conditions.1