Genetic and phenotypic analysis of elbow dysplasia in four large Swedish dog breeds : an evaluation of the screening programme and clinical symptoms

Sammanfattning: Elbow dysplasia (ED) is a common hereditary disease in dogs. Elbow dysplasia develops during the critical growth period between 4-12 months of age in large breed dogs and causes pain and lameness in the front limbs. In worst case it can lead to euthanasia. Therefore, a control programme (implemented different years for different breeds) through the Swedish Kennel Club is applied for ED to improve the health of affected breeds. However, few studies have investigated the association between screening results and clinical symptoms. The aim of this thesis was therefore to investigate if the screening results are well associated with the clinical symptoms. Furthermore, this thesis will investigate how many individuals with severe clinical symptoms that do not undergo the official screening in the control programme at the age of 12 months or older. Four breeds with high prevalence of ED were included in the study; Rottweilers, German Shepherd dogs, Labrador retrievers and Golden retrievers. Data from the official ED screening programme from the Swedish Kennel Club (SKK) database, as well as data from elbow related insurance claims from the insurance company Agria. Approximately 54 000 dogs had an official screening results, and 574 observations also had insurance claims for elbow related issues. Results showed that most of the dogs with an insurance claim were younger than the official screening age of 12 months. It was also shown that dogs with insurance claims generally had higher scores for ED compared with the general screened population. However, there was a high proportion of dogs with a normal screening result (ED score = 0) that still had an insurance claim, which was unexpected. The heritability for ED was between 0.13-0.20. Males, compared to females, had higher regression coefficients for inbreeding coefficient, weight at screening and age at screening related to ED. The conclusions are that the screening results seem to be a valuable indication of later ED-related clinical issues. However, a larger proportion of dogs than expected with an insurance claim had an official screening score of 0 (normal). The diagnosis fragmented coronoid process (FCP) had highest frequency in those dogs. Perhaps a second projection in the screening program could be beneficial in finding these cases. Also, the current routine control used today could perhaps be improved by including regressions nested within sex, litter effect and panellist. The results from this thesis should be interpreted carefully since the number of observations were few. Also, there was no guarantee that animals not included in the merged data were healthy since they could have been insured in another insurance company. However, Agria has the largest market share among all the insurance companies for pets. Moreover, more research is needed with a more complete data to validate the results from this thesis.