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WBFSH seminar - Kathrin-Friederike Stock


Kathrin-Friederike Stock (Photo:
Kathrin-Friederike Stock (Photo:
Selection for radiographic health of the limbs

Health of the locomotory system is a major determinant of the long-term performance ability of a horse, regardless of its use. Because X-rays of the limbs provide valuable information on certain orthopedic diseases, radiography of the equine limbs is extensively used for screening of young horses and in the course of pre-sale examinations. Given the importance of the radiographic status of a horse on the one hand and the costly and often very limited therapeutic options on the other hand, research and actions should mainly focus on preventive measures. Because breeding for improved health status is the most efficient preventive measure, extensive population genetic studies were performed in cooperation with the Hanoverian Society.
Investigations were based on the results of standardized radiographic examinations of the limbs of Hanoverian Warmblood horses intended for sale at auction between 1991 and 2004. Data referred to horses which were definitely offered at auction and horses which had to be withdrawn for different reasons (including inacceptable radiographic status). In the almost 8,000 horses examined in this time period, four radiographic findings were found to be quantitatively most important: osseous fragments in fetlock joints (OFF), osseous fragments in hock joints (OFH), deforming arthropathy in hock joints (DAH), and distinct radiographic changes in the navicular bones (DNB). Because the horses were young and clinically sound, the changes were often slight, but fit into the diseases complexes of osteochondrosis / osteochondrosis dissecans, bone spavin and navicular disease. According to literature, these diseases are frequently detected in horses of different age and breed and without clear correlation to lameness.
Subsequent genetic analyses of the radiographic data focussed on the previously identified main findings (OFF, OFH, DAH, DNB). Heritabilities of 0.1-0.3 indicated opportunities for selection for improved radiographic health of the limbs. Some of the additive genetic correlations between the four radiographic findings were significantly different from zero, so that breeding programs should be most efficient when considering the four traits separately and simultaneously.
Subsequent studies addressed the relationship between radiographic findings and performance. In particular, the compatibility of selection for improved radiographic health of the limbs with breeding progress regarding conformation and success in the main riding disciplines was studied. Investigations were based on a survey in owners of previous auction horses and on extensive data from competitions, studbook inspections, mare performance tests and auction horse inspections. In total, information on more than 26,000 horses entered the genetic analyses. Results supported the important role of radiographically visible alterations in the limbs of young riding horses in the context of successful and long-term use as sport horses. Conformation selection, particularly selection for regular limb stances and moderate withers height, was found to be in line with selection for radiographic health of the limbs. However, expected selection responses showed that relevant reduction of the prevalences of radiographic findings cannot be achieved by selection for dressage or jumping performance or by conformation selection alone. The study results consistently identified multiple-trait selection including radiographic health traits as feasible and the best measure to combine breeding progress in performance and radiographic health. Accordingly, the efforts of extensive screening and documentation of health data should finally pay off through increased efficiency and success of breeding programs which comprehensively account for conformation, performance and health.