Heritability of distichiasis in Havanese dogs in Norway.

Background: 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.

Results: 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 (h²_l = 0.664-0.674), corresponds well to the results of the Bayesian models.

Conclusions: 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.