Estimation of genetic population variables for six radiographic criteria of hip dysplasia in a colony of Labrador Retrievers

Objective-To estimate genetic population variables for 6 radiographic crite ria of canine hip dysplasia (CHD). Animals-664 full- and half-siblings from a colony of Labrador Retrievers. Procedure-Heritability estimates and genetic correlations were calculated f or 6 radiographic criteria of CHD. Two evaluation protocols were compared: the grade of the most severely affected hip joint and the sum of the scores for both hip joints. The predictive performance of estimated breeding valu es was also evaluated. Results-The overall prevalence of CHD (Federation Cynologique International e grades C, D, and E) was 29.6%. Median age at radiographic examination was 377 days. Heritability for the total CHD grade, Norberg angle (NA), covera ge of the femoral head (COV), craniodorsal acetabular rim (ACR), subchondra l bone sclerosis (SUBCH), shape of the femoral head and neck (FHN), and ost eoarthritic changes at the insertion site of the joint capsule (JC) was est imated as follows: 0.44, 0.43, 0.46, 0.37, 0.32, 0.21, and 0.05, respective ly. Heritability estimates were slightly higher for the sum of the scores f or both hip joints. If NA and COV were included as fixed effects in the mod el for the dependent variables ACR, SUBCH, FHN, and JC, then heritability o f these traits significantly decreased (0.08 to 0.15). High scores of NA an d COV lead to a significant increase of the scores of the remaining criteri a. Conclusions and Clinical Relevance-Canine hip dysplasia is heritable to a m oderate degree. Signs of subluxation revealed the highest heritability esti mates. The criteria ACR, SUBCH, FHN, and JC were strongly influenced by NA and COV.