Prevalence of genetic disorders in dog breeds: a literature review

Genetic disorders are common in dogs and in the media it is reported that genetic disorders are more frequent in pedigree dogs than in look-a-likes or in mixed-breed dogs. Here, we consider pedigree dogs as purebred dogs (i.e. matching a breed-specific morphology) with a registered and certified pedigree, whereas look-a-likes dogs are dogs without a certification. Thus, look-a-likes may be non-pure bred or purebred but lacking the supporting evidence. Dutch experts have indicated that more than 40 percent of purebred dogs in the Netherlands suffer from genetic disorders. Uncertainty about the validity of such indications, and if pedigree dogs are at increased risk of genetic disorders, together with societal concerns about the well-being of (pedigree) dogs, incited a Wageningen UR Science Shop project commissioned by the Dutch animal protection foundation Dier&Recht. Genetic disorders are heterogeneous in aetiology and manifestations across dog breeds, which complicates studying them. One feasible approach is to study specific disorders in pre-selected breeds only, as a model for the complex reality. This report, as part of this project’s products, provides a scientific literature overview on prevalence data for two genetic disorders (hip dysplasia and elbow dysplasia) in the German Shepherd and the Rottweiler in various countries including the Netherlands. The prevalence data assembled and compared in this study are based on results of screening programs published from national and international Kennel Clubs and Veterinarian Associations. In both breeds, the disease prevalence for hip dysplasia (HD), ranging from 10-46% in European and non -European countries, was remarkably variable, with a substantial proportion of the population at risk in, for example, Finland (33-46%). In the Netherlands, the prevalence for HD reported for both breeds (10-18%) was intermediate compared to that in other European countries (8-46%). Different methodology and scoring systems for HD are used in screening programs, whereas interpretations of radiographs to determine the HD grade, and the quality of databases, are critical factors. Methodological differences between studies make a valid comparison between studies difficult. The results for elbow dysplasia (ED) are similar regarding the high variation in prevalence among different countries (7-65%). However, the ED condition is estimated to be at least twice as prevalent in Rottweilers (40-60%) than in German Shepherds (20%). Yet, in the Netherlands, the estimated ED prevalence in both breeds is low (7-14%). This literature search found no data that allowed to test if the subcategory of look-a-likes are less affected by the specific genetic disorders HD and ED than pedigree dogs. Earlier studies have indicated that purebred dogs are more at risk of genetic disorders than mixed breed dogs, but this need not be the case for every disorder-dog breed combination. The detection of subtle differences in the prevalence of genetic disorders, for example between pedigree dogs and look-a-likes, require data that are presently unavailable as look-a-likes and mixed breeds are not nationally monitored for ED and HD