Influence of selective breeding on the prevalence of chorioretinal dysplasia and coloboma in the rough collie in Sweden

A total of 8204 rough collies, representing 76 per cent of ail collies regi stered by the Swedish Kennel Club between 1989 and 1997, were examined befo re 10 weeks of age for collie eye anomaly (CEA). All dogs were permanently identified acid examination results were registered and computerised. The p olicy of breeders during the study period was to select against coloboma in breeding stock, but to allow breeding of chorioretinal dysplasia (CRD) aff ected animals. The prevalence of CRD increased significantly from 54.2 per cent to 68.1 per cent (P < 0.001) from 1989 to 1997, while the prevalence o f coloboma did not (8.3 per cent to 8.5 per cent, P = 0.4). These results a re not compatible with a simple, recessive, autosomal inheritance for the e ntire CEA complex.