Chapter 23, Problem 27ESP

Canine hip dysplasia is a quantitative trait that continues to affect most large breeds of dogs in spite of approximately 40 years of effort to reduce the impact of this condition. Breeders and veterinarians rely on radiographic and universal registries to facilitate the development of breeding schemes for reducing its incidence. Data [Wood and Lakhani (2003). Vet. Rec. 152:69–72] indicate that there is a “month-of-birth” effect on hip dysplasia in Labrador retrievers and Gordon setters, whereby the frequency and extent of expression of this disorder vary depending on the time of year dogs are born. Speculate on how breeders attempt to “select” out this disorder and what the month-of-birth phenomenon indicates about the expression of polygenic traits.