Retrospective Analysis for Genetic Improvement of Hip Joints of Cohort Labrador Retrievers in the United States: 1970–2007

Abstract

BackgroundCanine Hip Dysplasia (CHD) is a common inherited disease that affects dog wellbeing and causes a heavy financial and emotional burden to dog owners and breeders due to secondary hip osteoarthritis. The Orthopedic Foundation for Animals (OFA) initiated a program in the 1960's to radiograph hip and elbow joints and release the OFA scores to the public for breeding dogs against CHD. Over last four decades, more than one million radiographic scores have been released.Methodology/Principal FindingsThe pedigrees in the OFA database consisted of 258,851 Labrador retrievers, the major breed scored by the OFA (25% of total records). Of these, 154,352 dogs had an OFA hip score reported between 1970 and 2007. The rest of the dogs (104,499) were the ancestors of the 154,352 dogs to link the pedigree relationships. The OFA hip score is based on a 7-point scale with the best ranked as 1 (excellent) and the worst hip dysplasia as 7. A mixed linear model was used to estimate the effects of age, sex, and test year period and to predict the breeding value for each dog. Additive genetic and residual variances were estimated using the average information restricted maximum likelihood procedure. The analysis also provided an inbreeding coefficient for each dog. The hip scores averaged 1.93 (±SD = 0.59) and the heritability was 0.21. A steady genetic improvement has accrued over the four decades. The breeding values decreased (improved) linearly. By the end of 2005, the total genetic improvement was 0.1 units, which is equivalent to 17% of the total phenotypic standard deviation.Conclusion/SignificanceA steady genetic improvement has been achieved through the selection based on the raw phenotype released by the OFA. As the heritability of the hip score was on the low end (0.21) of reported ranges, we propose that selection based on breeding values will result in more rapid genetic improvement than breeding based on phenotypic selection alone.

Trends in the phenotypic hip status of selected breeds of dog as measured by the New Zealand Veterinary Association Hip Dysplasia scheme (1990–2008)

“…An effect of gender on hip status was also reported in Estrela Mountain dogs, with females having greater hip laxity than males (Ginja et al 2008). This is in contrast to a much larger study in Labrador Retrievers using the OFA data, in which no effect of gender on score was found (Hou et al 2010). It has been proposed that endogenous oestrogen can affect a joint's laxity, but this was not the case in a prospective study of bitches in oestrus (Hassinger et al 1997).…”

“…Similarly, increasing age at scoring was associated with increasing dysplastic OFA scores in Labrador Retrievers (Hou et al 2010). Therefore, as a dog ages, its hip-extended score is a more accurate predictor of hip status at the end of life.…”

“…An analysis of breeding value of the phenotype of 154,352 Labrador Retrievers, measured on extended-hip radiographs, reported by the OFA, resulted in a heritability estimate of 0.21 (Hou et al 2010). Investigators from the University of Pennsylvania have reported the distraction index to have an estimated heritability of between 0.34 and 0.73, using various methodologies including analysis of full pedigrees and inter-class correlation coefficients (Kapatkin et al 2002).…”

“…Selection on phenotypes is as accurate as selection based on breeding values only when heritability is close to one (Hou et al 2010). As suggested by Burbidge (2003), calculation of breeding values from pedigree information would provide a much better selection tool for dog breeders in New Zealand, independent of the scoring scheme used.…”

“…the OFA data based on estimated breeding values indicated that over a 40-year period the hip phenotype for Labrador Retrievers only reduced by 0.1 units, equivalent to a 5% decrease on an ordinal scale from 1 to 7(Hou et al 2010).…”