Heritability of distichiasis in Havanese dogs in Norway

Abstract

Distichiasis is a presumed inherited eyelid disease, characterized by misplaced eyelashes. The effect on eye health and animal welfare varies between individuals; most mild cases show no clinical signs, but some affected animals develop painful corneal disease. In this study, we investigated the prevalence and heritability of distichiasis in the Norwegian population of Havanese dogs. A total of 1156 Havanese were included in the study. Out of these, 168 were affected with distichiasis, making the prevalence in our sample 14.5% (95% CI 12.5–16.6%). There was no sex predisposition. Most affected individuals were graded “mildly affected”. The estimates generally showed high heritabilities, which varied between 0.276 (linear model) and 0.720 (Bayesian threshold model). The linear estimates, after conversion to the underlying scale (h2l = 0.664–0.674), corresponds well to the results of the Bayesian models. The estimated heritability of distichiasis in Havanese is high and the prevalence is moderate. The high heritability indicate that a significant selection response could be obtained by simple mass selection. To secure good animal welfare, it’s important to control the number of affected individuals and especially the severely affected. Distichiasis is an eye condition, characterized by misplaced eyelashes, that is frequently seen in dogs. Some dog breeds appear to be more at risk than others. The degree of clinical signs in affected dogs varies a lot. Many mild cases appear to be completely asymptomatic, while others suffer pain and damage to the eye, which necessitates removal of the hairs. In this study, we investigate both how common distichiasis is in the Havanese dog breed and estimate the degree of genetic influence on the trait. We find that 14.5% of eye screened Havanese, registered in the Norwegian Kennel Club, are affected with distichiasis. Most cases are graded “mild”. There is no significant difference in how many males and females are affected. We find high heritability estimates of distichiasis in Havanese (≈0.28 calculated by linear models and 0.59-0.72 calculated by Bayesian threshold models), showing a high genetic influence on the trait. The high estimated heritability mean that it should be possible to reduce the prevalence of the condition, and contribute to improved animal welfare, though systematic breeding. We recommend that all Havanese are eye screened prior to breeding, to control the prevalence of distichiasis, as well as other eye conditions that are relevant in the breed, like cataracts. Dogs with severe distichiasis or ectopic cilia should not be bred. Dogs with mild or moderate distichiasis may be bred to an unaffected partner.