Genetic improvement of hip-extended scores in 3 breeds of guide dogs using estimated breeding values: Notable progress but more improvement is needed

Abstract

Two hip quality phenotypes—a hip-extended score assigned by a board certified radiologist and the PennHIP distraction index—were analyzed to estimate genetic parameters and to calculate estimated breeding values used for selecting replacement breeders. Radiographs obtained at 12–18 months of age were available on 5,201 German Shepherd Dogs, 4,987 Labrador Retrievers and 2,308 Golden Retrievers. Obtained by fitting a two-trait model using Bayesian techniques, estimates of heritability for the hip-extended score were 0.76, 0.72, and 0.41 in German Shepherd Dogs, Labrador Retrievers, and Golden Retrievers, respectively, while estimated heritabilities for distraction index were 0.60, 0.66 and 0.59, respectively. Genetic correlations between the two hip quality measures were −0.28 in German Shepherd Dogs, −0.21 in Labrador Retrievers, and −0.29 in Golden Retrievers. Genetic selection for improved hip quality based upon the hip extended score phenotype began in 1980. Among first generation puppies, 34% of 273 German Shepherd Dogs, 55% of 323 Labrador Retrievers, and 43% of 51 Golden Retrievers had an Excellent hip extended score. After 8 generations of selection, mostly based on estimated breeding values derived from the hip extended score, over 93% of 695 German Shepherd Dogs, 94% of 528 Labrador Retrievers, and 87% of 116 Golden Retrievers received an Excellent hip extended score. With respect to PennHIP distraction index values among these same dogs, median values were at or above 0.30 for all 3 breeds meaning that half or more of dogs possessing the Excellent hip-extended-score phenotype remained susceptible to developing the osteoarthritis of canine hip dysplasia. Genetic improvement of the hip-extended-view phenotype to its desired biological endpoint left a surprising proportion of dogs expressing sufficient joint laxity to place them in an osteoarthritis at-risk state as they age. Only by directly applying selection pressure to reduce distraction index was marked reduction in joint laxity noted.

Prevalence of canine hip dysplasia in 10 breeds in France, a retrospective study of the 1997-2017 radiographic screening period

“…There is still a margin for improvement in this breed, although it showed the largest improvements in the prevalence of HD. These results are consistent with previous studies indicating that selective breeding using classifications of hip joint phenotypes might improve hip conformation in several breeds of dogs [5,7,10,11,12,13,14,15,16], although other studies showed different findings, and the efficiency of using screening programs to reduce the prevalence of HD has been questioned [17,18,19,20].…”

“…A previous study demonstrated that when all dogs in a breed have nearly the same hip phenotype, almost no selection pressure can be applied to improve hip quality based on hip radiograph screening [ 14 ]. According to the results of the present study, this was potentially the case for the Siberian Husky and for the Australian Shepherd dog, which demonstrated slight changes in HD prevalence.…”

“…In these countries, an HD control program gives a good overall prevalence for each breed. A study demonstrated that an improvement in hip quality can be achieved by selection based on the subjective scoring of radiographs when all dogs of a breed are evaluated [14].…”

“…Several control programs have been conducted in different countries over the last 25 years, and their ability to reduce hip dysplasia has shown variable results. While several reports identified a decrease in HD prevalence [5,7,10,11,12,13,14,15,16], others failed to identify any significant progress [17,18,19,20].…”

Rejections in an non-purpose bred assistance dog population: Reasons, consequences and methods for screening

“…[50,51] In more detail, it has for example been demonstrated that 10 generations suffice to get initial hip dysplasia prevalences of 40 to 50 percent to zero. [52] To achieve this genetic progress, a subset of the population of the dogs is selected to be used in breeding programs and this selection can be done based on genomic prediction or estimated breeding values. [53,54] In these breeding programs, other screening criteria can be added when necessary (for example, screening for heart disorders, ophthalmologic screening and genetic tests).…”