Genetic Selection Reduces Canine Hip and Elbow Dysplasia Prevalence Over Time

Canine hip dysplasia (CHD) and elbow dysplasia (ED) prevalence was reduced by long-term genetic selection, according to a study recently published in PLoS ONE.

CHD and ED are heritable orthopedic conditions that manifest themselves after birth. Reducing CHD incidence has primarily involved making breeding decisions using phenotypic radiographic evidence of the disease.

Heritability describes the extent of genetic influence on phenotypic variation. Previous studies have reported wide ranges of heritability estimates for CHD and ED, in part due to breed variation. Other studies have reported low genetic correlation between CHD and ED, indicating distinct genetic regulation of each disease.

Study authors collected hip and elbow ratings data between 1970 and 2015 from the Orthopedic Foundation for Animals (OFA) database. Data were collected only for dogs 2 years of age or older at evaluation and for breeds with all required hip and elbow evaluations. Ratings ranged from 1 (excellent) to 7 (severe) for hips and from 1 (normal) to 4 (degenerative joint disease grade III) for elbows.

Prevalence and Heritability

The authors first determined CHD and ED prevalence within each of the 60 analyzed breeds. CHD prevalence was highest in Newfoundlands and bloodhounds (25%) and lowest in Belgian sheepdogs (2.8%). ED prevalence was highest for chow chows (49%) and lowest for Briards (0.2%). Several breeds had high CHD and ED prevalence.

Sex and age effects on hip and elbow ratings were also measured. Hip ratings were significantly better in males than in females in some breeds and vice versa in other breeds; ED ratings were significantly better in males than in females only for one breed (Rhodesian ridgebacks). Regarding age, hip ratings were slightly worse in older dogs than in younger dogs in about half of the breeds; interestingly, for 3 breeds, elbow ratings were better in older dogs.

Average heritability estimates were 0.57 (range, 0.46—0.75) for CHD and 0.29 (range, 0.01–0.90) for ED. Almost 90% of breeds had heritability estimates over 0.50, supporting the use of genetic selection to lower disease incidence.

Genetic correlation between CHD and ED was highly variable, ranging from near-perfect correlation (0.99) for 2 breeds (Alaskan malamutes and Nova Scotia duck trolling retrievers) to negative correlation for other breeds.

Genetic and Phenotypic Progress

The authors selected several breeds to assess estimated breeding values (EBVs), a measure of the genetic risk of passing on a specific trait—for this study’s purposes, CHD or ED. EBVs can be used to determine genetic and phenotypic progress, but they do not directly indicate disease severity.

For CHD, high- and low-prevalence breeds demonstrated decreased EBVs over time. The percentage of hips rated “excellent” increased during this time, most markedly for Newfoundlands and Rottweilers (both high-prevalence breeds). Phenotypic improvement for the low-prevalence breeds reflected the mindfulness of breeders to reduce CHD incidence, even in low-risk dogs.

For ED, EBVs and the percentage of “normal”-rated elbows remained relatively constant over time for high- and low-prevalence breeds.

EBVs were also used to evaluate maternal and paternal impact on hip conformation in selected breeds. Conformation was significantly more impacted by sires than dams.

Voluntary radiographic screening was noted as a study limitation, making OFA database information incomplete. The authors emphasized increasing screening participation, which breed clubs and registry bodies continue to encourage.

Overall, the study’s findings indicate steady improvement of hip and elbow conformation with genetic selection; it is possible that this improvement could be more rapid with genetic rather than phenotypic selection. Importantly, the authors noted that the results “demonstrate variability of breeds and underscore the clear need to consider the individual breed when assessing disease liability.”

Dr. JoAnna Pendergrass received her doctorate in veterinary medicine from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, LLC.