Genetic and environmental risk factors for vitiligo and melanoma in Pura Raza Español horses.
Authors: Sánchez-Guerrero M J, Solé M, Azor P J, Sölkner J, Valera M
Journal: Equine veterinary journal
Summary
Vitiligo and melanoma represent significant clinical concerns in grey Pura Raza Español horses, with prevalence rates of 2.8–20.5% for vitiligo (depending on anatomical site) and 1.6% for melanoma; this study investigated both the heritability of these conditions and the environmental factors influencing their expression across a global population of 11,436 horses using Bayesian genetic modelling. Age, coat colour and inbreeding coefficient all emerged as significant environmental contributors to disease manifestation, whilst heritability estimates varied considerably by phenotype—nostril vitiligo showed moderate heritability (0.44), whilst eye vitiligo and melanoma demonstrated lower heritability (0.09 and 0.13 respectively), suggesting environmental factors play a more substantial role in the latter two presentations. The moderate genetic correlation between eye and nostril vitiligo (0.42) indicates some shared genetic basis, yet the weak correlation between nostril vitiligo and melanoma (0.15) suggests these may have largely distinct aetiological pathways. These findings support the inclusion of vitiligo and melanoma scoring in breeding programme selection criteria—particularly for nostril vitiligo, where genetic merit can be more effectively improved—whilst also highlighting that managing inbreeding coefficients and potentially selecting for lighter coat patterns may help reduce overall prevalence in susceptible bloodlines.
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Practical Takeaways
- •These conditions are common in grey horses and have a heritable component; breeding decisions should consider vitiligo and melanoma scores alongside pedigree analysis to reduce prevalence
- •Environmental factors including age and coat colour influence disease expression, so management strategies tailored to these risk factors may help minimize clinical signs
- •The moderate heritability of nostril vitiligo (0.44) suggests selective breeding against this trait is feasible and could meaningfully reduce prevalence in the population
Key Findings
- •Vitiligo prevalence was 2.8% around eyes and 20.5% around nostrils, with melanoma present in 1.6% of Pura Raza Español horses
- •Heritability estimates were 0.09 for eye vitiligo, 0.44 for nostril vitiligo, and 0.13 for melanoma, indicating both genetic and environmental contributions
- •Age, coat colour, and inbreeding were significantly associated with all three conditions studied
- •Genetic correlation between nostril and eye vitiligo was 0.42, while correlation between nostril vitiligo and melanoma was 0.15