Scope for a threshold animal model for genetic evaluation for hip dysplasia.

Abstract

Hip dysplasia (HD) is a major welfare problem, and in the present work, we investigated a sample of Bernese Mountain Dog breed bred in Brazil to estimate the genetic parameters for HD and to determine the best model for the estimation of breeding values (EBV) of dogs. The pedigree database consisted of 2218 dogs, of which 1202 had the hip phenotype available, corresponding to the X-ray (XR) classification according to the Fédération Cynologique Intenationale. Comparisons were made between seven different threshold models considering the HD phenotype with five classifications (reports from A to E) according to the XR (PHD1) and the binary phenotype with joints considered normal (report A) and abnormal (reports B to E) (PHD2). The threshold animal model was used to estimate the variance components and predict the genetic values. Fourteen models were evaluated, seven using variable PHD1 and another seven considering variable PHD2. Evaluated fixed effects were sex, birth year, or country of birth, which differed between models. The best fit model for the PHD1 phenotype estimated a heritability value of 0.30, while the best fit model for PHD2 estimated a value of 0.36. EBVs ranged from - 0.736 to 1.040 for PHD1 and from - 1.050 to 1.459 for PHD2, showing a wide diversity in the genetic merit of dogs. Approximately 40% of the animals had an EBV accuracy value greater than 50%. Considering the best two fit models for the tested phenotypes, we opted for the indication and use of the model working with PHD1, because of the direct correspondence of the PHD1 phenotype with the five possibilities of hip XR reports, once this facilitates understanding by both veterinarians and breeders. This model is used as the only fixed effect of the birth year. The present study is one of the first on canine genetic improvement approach in Brazil, and our results indicate the importance and potential of the use of EBV in the selection of sires for the improvement of HD in the national breeding of the breed.