Collie eye anomaly in the rough collie in Sweden: genetic transmission andinfluence on offspring vitality

Between 1989 and 1997, 8204 rough collies were examined for collie eye anom aly (CEA) at up to 10 weeks of age. All dogs were positively identified and the results were registered under the Swedish Kennel Club genetic health p rogramme. A significant decrease in litter size occurred if one of two affe cted parents had coloboma (3.8 pups) compared with litters from two chorior etinal dysplasia- (CRD-) affected collies (5.2 pups) or litters by two norm al collies (5.0 pups), indicating an influence of the coloboma genotype on offspring vitality. The prevalence of CRD in pups from normal x normal mati ngs and CRD x CRD matings was significantly different from that expected un der simple autosomal recessive inheritance (43 per cent versus 25 per cent and 85 per cent versus 100 per cent), The results are compatible with polyg enic inheritance but not with simple autosomal recessive inheritance. CRD p revalence in offspring of CRD x coloboma matings was significantly lower th an in pups of CRD x CRD matings, reflecting effects of the coloboma genotyp e on vitality. These results have important implications for breeding progr ammes and the genetic control of CEA.