Genetic Evaluation of Hip Score in UK Labrador Retrievers

Hip dysplasia is an important and complex genetic disease in dogs with both genetic and environmental influences. Since the osteoarthritis that develops is irreversible the only way to improve welfare, through reducing the prevalence, is through genetic selection. This study aimed to evaluate the progress of selection against hip dysplasia, to quantify potential improvements in the response to selection via use of genetic information and increases in selection intensity, and to prepare for public provision of estimated breeding values (EBV) for hip dysplasia in the UK. Data consisted of 25,243 single records of hip scores of Labrador Retrievers between one and four years old, from radiographs evaluated between 2000 and 2007 as part of the British Veterinary Association (BVA) hip score scheme. A natural logarithm transformation was applied to improve normality and linear mixed models were evaluated using ASREML. Genetic correlations between left and right scores, and total hip scores at one, two and three years of age were found to be close to one, endorsing analysis of total hip score in dogs aged one to three as an appropriate approach. A heritability of 0.35±0.016 and small but significant litter effect (0.07±0.009) were estimated. The observed trends in both mean hip score and mean EBV over year of birth indicate that a small genetic improvement has been taking place, approximately equivalent to avoiding those dogs with the worst 15% of scores. Deterministic analysis supported by simulations showed that a 19% greater response could be achieved using EBV compared to phenotype through increases in accuracy alone. This study establishes that consistent but slow genetic improvement in the hip score of UK Labrador Retrievers has been achieved over the previous decade, and demonstrates that progress may be easily enhanced through the use of EBVs and more intense selection.

犬髋关节发育不良（hip dysplasia）是犬类中一种重要且复杂的遗传疾病，同时受遗传与环境因素共同影响。由于其继发的骨关节炎具有不可逆性，因此通过降低患病率以提升动物福利的唯一途径便是开展遗传选育。本研究旨在评估抗髋关节发育不良选育的进展，量化通过利用遗传信息以及提高选育强度所可能带来的选育响应提升，并为英国境内犬髋关节发育不良估计育种值（EBV, estimated breeding values）的公共发布工作做好准备。
研究数据共包含25243条拉布拉多寻回犬的髋关节评分单条记录，受试犬年龄介于1至4岁之间，其髋关节X光片于2000年至2007年间完成评估，相关数据隶属于英国兽医协会（BVA, British Veterinary Association）髋关节评分计划。为改善数据正态性，我们对其实施了自然对数变换，并采用ASREML软件对线性混合模型进行评估。
研究发现，左右侧髋关节评分之间，以及1、2、3岁时的总髋关节评分之间的遗传相关性均接近1，这证实了对1至3岁犬只的总髋关节评分开展分析是合理的研究方法。本研究估算得到的遗传力为0.35±0.016，同时存在微小但显著的窝效应（0.07±0.009）。
不同出生年份的平均髋关节评分与平均估计育种值的变化趋势均显示，过去十年间犬群已实现了小幅的遗传改良，其效果大致相当于淘汰评分最差的15%的个体。
辅以模拟的确定性分析结果表明，仅通过提升准确性，利用估计育种值开展选育可比基于表型的选育获得19%更高的遗传进展。本研究证实，在过去十年间，英国拉布拉多寻回犬的髋关节评分已实现了持续但缓慢的遗传改良，并证明通过使用估计育种值以及强化选育，可轻松提升选育进展。