Heritability and Phenotypic Variation of Canine Hip Dysplasia Radiographic Traits in a Cohort of Australian German Shepherd Dogs

Abstract

Canine Hip Dysplasia (CHD) is a common, painful and debilitating orthopaedic disorder of dogs with a partly genetic, multifactorial aetiology. Worldwide, potential breeding dogs are evaluated for CHD using radiographically based screening schemes such as the nine ordinally-scored British Veterinary Association Hip Traits (BVAHTs). The effectiveness of selective breeding based on screening results requires that a significant proportion of the phenotypic variation is caused by the presence of favourable alleles segregating in the population. This proportion, heritability, was measured in a cohort of 13,124 Australian German Shepherd Dogs born between 1976 and 2005, displaying phenotypic variation for BVAHTs, using ordinal, linear and binary mixed models fitted by a Restricted Maximum Likelihood method. Heritability estimates for the nine BVAHTs ranged from 0.14–0.24 (ordinal models), 0.14–0.25 (linear models) and 0.12–0.40 (binary models). Heritability for the summed BVAHT phenotype was 0.30±0.02. The presence of heritable variation demonstrates that selection based on BVAHTs has the potential to improve BVAHT scores in the population. Assuming a genetic correlation between BVAHT scores and CHD-related pain and dysfunction, the welfare of Australian German Shepherds can be improved by continuing to consider BVAHT scores in the selection of breeding dogs, but that as heritability values are only moderate in magnitude the accuracy, and effectiveness, of selection could be improved by the use of Estimated Breeding Values in preference to solely phenotype based selection of breeding animals.

Monitoring Hip and Elbow Dysplasia Achieved Modest Genetic Improvement of 74 Dog Breeds over 40 Years in USA

“…Estimates of heritability reported in papers based on the BVA/UK registry are based on the entire population of dogs’ hip phenotypes rather than only publicly accessible records, while our analysis is based only on publicly accessible records. As well, based on the BVA scheme, a range of 0.14–0.25 was also reported by using a linear model in a cohort of Australian German shepherd dogs [21]. It was indicated that the discrepancy in estimates of heritability for hip scores was attributed to distinct evaluation schemes and populations.…”

Estimated Breeding Values for Canine Hip Dysplasia Radiographic Traits in a Cohort of Australian German Shepherd Dogs

“…All data sets included all data available electronically at the time at which the records were obtained. Details of the data set are available in [11]. The data set contains the animal’s name, pedigree information, year of birth, age at radiographic study, sex and scores for each of the 18 BVAHTs.…”

“…The final data set analysed in this study comprised records from 13,124 (8,793 female, 4,331 male) GSDs born in Australia between 1976 and 2006. Completeness of the data set was investigated by matching scores against the pedigree file for Australian-born GSDs and is reported in [11]. A detailed description of the nature of the data, including a distribution of scores, is also provided in [11].…”

“…Using mixed-model equations, an EBV can be calculated for a particular trait based not only on the candidate’s phenotypic score but all relevant information such as scores from relatives (who share alleles with the candidate to a predictable extent), scores from related traits which may be due to the actions of some of the same genes, and, when available, molecular information regarding some of the many germane genes. Most published estimates of the heritability of CHD radiographic phenotypes have been within the range 0.2 to 0.6 [11]. Selection on traits with heritabilities in this range can most definitely benefit from the use of EBVs.…”

“…It has also been shown from the same Australian GSD data sets that the nine traits can usefully be grouped on the basis of the magnitude of their phenotypic variance into the more variable “Group 1” traits of Norberg Angle (NORB), Subluxation (SUBL) and Cranial Acetabular Edge (CrAE), and the substantially less variable “Group 2” traits of Dorsal Acetabular Edge (DAE), Cranial Effective Acetabular Rim (CrEAR), Acetabular Fossa (AF), CaAE, Femoral Head and Neck Exostosis (FHNE) and Femoral Head Remodelling (FHR) [11]. Lewis et al [17] proposed the same grouping in a study of BVAHTs of Labrador Retrievers from the United Kingdom, based on the reality that Group 1 traits tend to reflect morphological malformations and Group 2 traits reflect mainly pathological signs of osteoarthritis.…”