Summary Background Vitiligo and melanoma are relatively common disorders in grey Pura Raza Español horses and other horse breeds with grey‐coloured coats. Objectives To determine the breed prevalence, environmental risks factors and estimate the genetic parameters for vitiligo and melanoma in Pura Raza Español horses. Study design Retrospective cohort study. Methods We analysed data from a large worldwide population of Pura Raza Español horses. The database included the vitiligo and melanoma scores, on either a four‐ or six‐point linear scale, of 11,436 horses. Genetic parameters were estimated using a Bayesian genetic animal model including the four associated environmental risk factors as systematic effects. Inbreeding was used as a covariate, and animal and residual effects were included as random effects. Results Of the horses included in the study, 2.8 and 20.5% showed some traces of vitiligo around the eyes and mouth, respectively, while 1.6% showed varying degrees of melanoma. Age, coat colour and inbreeding were significantly associated with the three outcomes studied. The estimated heritability for the whole population was 0.09 (s.d. +0.019), 0.44 (s.d. +0.031) and 0.13 (s.d. +0.037), for eye vitiligo score, nostril vitiligo score and melanoma scores respectively. The genetic correlations ranged from 0.42 (s.d. +0.084) between eye and nostril vitiligo score to 0.15 (s.d. +0.096) between nostril vitiligo and melanoma. Main limitations Vitiligo scores for the perianal regions were not collected. The veterinarian responsible for each assessment was not recorded. Conclusions Vitiligo and melanoma are prevalent in this population and those environmental risk factors and genetics both have an effect on the clinical expression of the diseases. These findings may help to reduce prevalence through breeding programmes.

No abstract