Breeding for improved hip and elbow health in Swedish dogs

Decades of selective breeding to reduce the prevalence of hip and elbow dysplasia(HD and ED) in Swedish dogs, based on phenotypic assessment of radiographic hip status, has had limited success. The prevalence of dysplastic dogs is still high in many large-sized and giant breeds and among the most common causes for euthanasia and costly veterinary care in numerous breeds are joint-related problems. The aim of this thesis was to investigate the possibilities of more efficient breeding strategies for improved hip and elbow health in Swedish dogs by improving the genetic evaluation of HD and ED, and by evaluating the clinical significance of radiographic hip status. Data from several different sources were combined in the analyses: pedigree information and screening records for HD and ED from the Swedish Kennel Club, questionnaire data about routines for hip and elbow screening from Swedish veterinary clinics and insurance data on hip-related veterinary care and mortality from Agria Insurance Company. Moreover, simulated data were used to evaluate selection strategies. Radiographic hip status in young adult dogs was shown to be strongly associated with subsequent incidence of veterinary care and mortality related to the hip joint. Furthermore, the genetic analyses of screening records for HD and ED showed considerable genetic variation and moderate heritability of both traits. Taken together, these findings support the use of screening records for HD and ED in selection to reduce prevalence of clinical problems related to hip and elbow joints. However, the impact of systematic environmental factors, such as sedation method, on the phenotypic expression of HD and ED implies that the individual’s screening result alone is an imprecise estimate of its breeding value. Simulation of selection strategies against HD showed that selection based on BLUP breeding values was superior to phenotypic selection, leading to faster genetic progress and more rapid reduction of dysplastic dogs. Based on the studies included in this thesis, it is concluded that implementation of breeding schemes based on BLUP breeding values, instead of phenotypic records, should be prioritised to enable a more efficient breeding for improved hip and elbow health in Swedish dogs.