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

Eldin A Leighton,Mandy L Wallace,Jennifer K Reagan,Darryl N Biery,Gail K Smith,Thomas P Gregor,Dolores Holle,Mischa B Mcdonald-Lynch,Claire Wade

doi:10.1371/journal.pone.0212544

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.

Highlights

Canine hip dysplasia (CHD) is a highly prevalent orthopedic disease [1] of complex inheritance [2] [3] [4], meaning many genes and environmental factors [5] are responsible for phenotypic expression of the disorder
The 2,948 dogs without a distraction index (DI) measurement were, for the most part, dogs that passed through the system prior to the beginning of distraction radiography in 1991
Fewer than 100 dogs born prior to 1990 had DI values recorded, and when a DI value was recorded for these older dogs, it was usually obtained as part of the routine physical given to retiring breeders

Summary

Introduction

Canine hip dysplasia (CHD) is a highly prevalent orthopedic disease [1] of complex inheritance [2] [3] [4], meaning many genes and environmental factors [5] are responsible for phenotypic expression of the disorder. The disease phenotype is characterized by hip joint laxity in young dogs that, with age, often leads to development of secondary osteoarthritis (OA) [6] [7]. Genetic control aims to reduce CHD prevalence in future generations by selecting young breeding dogs possessing a genetic predisposition to produce offspring with reduced genetic susceptibility for developing CHD. This strategy requires an accurate hip screening test for use in individual dogs, and it requires utilizing time-proven animal breeding methods [13] to accurately identify exactly which young dogs are most likely to produce new offspring with low genetic risk of developing OA of CHD

Methods

Results

Discussion

Conclusion