10 October 2017

Recommendations for the best selection method

Reducing genetic diseases in the Cavalier King Charles spaniel

In 2009, the Cavalier King Charles spaniel (CKCS) became world news for a very unfortunate reason. The BBC documentary ‘Pedigree Dogs Exposed’ discussed the condition chiari malformation and syringomyelia (CM/SM). The documentary determined that the CKCS had a skull that was too small, which caused CM/SM in the breed. Since then, many new publications have added some nuance to the debate. CM/SM are two conditions that are caused by multiple defects of both skeletal and soft tissue. These new insights have disproven the simplistic theory that the condition is caused by having too small a skull. The disease is probably due to a complex of genetic factors, which makes selecting for the disease much more complicated.

As a result of the BBC documentary, purebred dogs in general and CKCS in particular have become the subject of heated debate. At the initiative of former State Secretary Henk Bleker and the Neurology department at the University Clinic for Companion Animal Health, the Dutch Cavalier Club and the Dutch Kennel Club (Raad van Beheer) have signed a covenant in order to make the breed more healthy. Starting in 2011, all CKCS dogs used for breeding must be screened using techniques such as MRI scans. 

Three evaluation systems are available. The oldest method, in which the dogs are divided into four groups, does not result in a clear reduction of the condition, so the British Veterinary Association and the British Kennel Club have suggested an improved method, the BVA/KC scheme. However, selection using this method (article pending) only shows a gradual improvement, so a more detailed phenotyping evaluation method is used, involving more precise measurements and considering the dog’s age. Together with the Livestock Genetics research group at Leuven University, researchers have determined the degree of heritability for the BVA/KC method and the more detailed phenotyping method. CM occurs in almost all CKCS dogs, so it should perhaps be considered as one of the breed’s characteristics. However, this does not apply for SM. When using the BVA/KC method, the heritability index for SM is only 0.13, and with improved phenotyping it improves to 0.3. The heritability index is a way to describe the degree of heritability of a trait, and the possibility of selection. A value of 0.3 is not extremely high, but it does mean that selection is possible with optimal phenotyping. The current BVA/KC method does not offer sufficient control. As a result, the researchers from Utrecht and Leuven have concluded that the third measurement method is a much more effective instrument to reduce the occurrence of SM.

Read the article: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0184893

This study was previously conducted as a Master’s research by Wieteke Eggelmeijer (Faculty of Veterinary Medicine, Utrecht University), and was part of the PhD research by Katrien Wijnrocx (KU Leuven). The study was conducted under the supervision of Paul Mandigers, as one of the studies within the Expertise Centre Genetics of Companion Animals (ECGG) and Advanced Veterinary Research (AVR). The study was financed by an external party.