Selection for breed-specific long-bodied phenotypes is associated with increased expression of canine hip dysplasia

Hip dysplasia (HD) is the most common skeletal disease in purebred dogs. Radiographic schemes developed to reduce prevalence through selective breeding have had limited success, but the role of selecting for morphological characteristics prized in the show-ring and dictated by breed standards has not been fully explored. This study correlated published scores of hip pathology with measurements of body length to height ratio from photographs of Best-of-Breed specimens from 30 breeds (n=12/breed) to establish whether selection criteria could be compromising welfare by increasing susceptibility to HD. Relative body length correlated strongly with higher rates of HD by breed data from the Orthopedic Foundation for Animals (Spearman r=0.727, P<0.001), the British Veterinary Association (r=0.701, P<0.001), and the Australian Veterinary Association (r=0.577, P<0.01). By favouring body shapes that are longer than they are tall, judges may be inadvertently selecting for conformational attributes predisposing dogs to HD, suggesting that ambiguity in breed standards and extreme relative body length phenotypes can engender serious welfare consequences and need to be re-evaluated.