Quantitative genetics of canine hip dysplasia in a population of Australian-born German shepherd dogs (Canis familiaris)

Abstract

Welfare deficits from canine hip dysplasia (CHD), arising from pain and dysfunction in the coxofemoral joint, are a substantial concern. As CHD is a partly inherited, multifactorial condition, the reduction of welfare deficits from CHD by selective breeding, is of paramount importance. Traditionally, selective breeding against CHD in Australia has been accomplished via radiographic examination of young adults. Such radiographs are scored using the British Veterinary Association/Kennel Club (BVA/KC) scoring scheme, an ordinal assessment of nine traits in each hip. As many authors have argued, the moderate heritability of CHD suggests a that more accurate assessment of breeding candidates could be accomplished by calculating Estimated Breeding Values (EBVs) from CHD scores. This question has been assessed for BVA/KC-like schemes in the UK using models which assume that the BVA/KC CHD traits are linear, although, as noted above, the BVA/KC CHD traits are, in fact, ordinal, meaning EBVs calculated assuming linearity are based on un-evidenced assumptions. This thesis develops BVA/KC CHD trait EBVs using models which recognise the ordinal nature of the BVA/KC CHD traits and considers binary and ordinal models as the potential basis for an EBV for BVA/KC CHD traits within a population of Australian German Shepherd Dogs (GSDs). BVA/KC CHD scores and pedigrees from 13,124 GSDs born 1976-2006 are examined. High phenotypic and genotypic correlations between traits in the left and right hip are found. Moderate heritability of the CHD traits in this population is confirmed and EBVs are calculated using binary, ordinal and linear models. A beneficial trend found in the average EBV over time provides evidence for genetic improvement in the GSD population over the studied decades. The genetic correlations between the CHD traits are examined. Two selection indexes based on the ordinal model EBVs are proposed as a basis for future selection in this population.