Since 1966, the Orthopedic Foundation for Animals (OFA) has been collecting data on hip joint phenotypes in purebred dogs to attempt to achieve one of their objectives: to lower the incidence of orthopedic and genetic diseases. The OFA uses three randomly selected veterinary radiologists from a pool of 20 to 25 to examine and classify each owner-submitted pelvic radiograph. They classify normal hips as being excellent, good, or fair and hips with signs of dysplasia as being mild, moderate, or severe. This assigned classification can then be used to assist an owner in determining whether or not to use the individual dog for breeding.
This retrospective cohort study from Veterinary Surgery used OFA data to examine whether, over time, removing dogs with undesirable hip joint phenotypes from the breeding population (selective breeding based on OFA classification) has had an impact on the hip joint classifications in the population of dogs evaluated by the OFA. In a previous study also using data from the OFA, the number of dogs whelped from 1989 to 1992 that were classified as having excellent hips was higher compared with dogs whelped from 1972 to 1980. The present study examined the OFA classifications of 431,483 dogs whelped from 1989 to 2003.
The most common breeds found to be evaluated by the OFA in this study were Labrador retrievers, golden retrievers, German shepherds, rottweilers, and Bernese mountain dogs. Compared with dogs whelped from 1989 to 1992, dogs evaluated in this study were significantly more likely to have their hips classified as excellent or good. Labrador retrievers had the highest percentage of good (59.8%) and excellent (19.4%) hips, while rottweilers had the highest percentage of mild, moderate, or severe radiographic classifications of hip dysplasia (16.9%). Males were slightly more likely to have excellent and fair hip classifications, and females were slightly more likely to have mild, moderate, or severe canine hip dysplasia classifications. Although these sex associations were statistically significant, the authors suggest that the associations were small enough as to possibly be clinically insignificant.
The results of both studies reveal that percentages of pure bred dogs classified by the OFA as having radiographically evident hip dysplasia are decreasing. However, the subjects in these studies had a self-selection bias because owners had to voluntarily submit radiographs to the OFA for evaluation (e.g. owners of animals with radiographs likely to be classified as dysplastic may not readily submit their dogs’ radiographs to the OFA for classification), so these results cannot be generalized to the entire dog population.
Kaneene JB, Mostosky UV, Miller R. Update of a retrospective cohort study of changes in hip joint phenotype of dogs evaluated by the OFA in the United States, 1989-2003. Vet Surg 2009;38:398-405.
Link to abstract: http://www3.interscience.wiley.com/journal/122297360/abstract