Spotting the Pattern: A Review on White Coat Color in the Domestic Horse.
Authors: McFadden Aiden, Vierra Micaela, Martin Katie, Brooks Samantha A, Everts Robin E, Lafayette Christa
Journal: Animals : an open access journal from MDPI
Summary
White coat patterning in horses represents far greater genetic complexity than base coat colour, with over 50 identified mutations capable of producing white markings compared to just two markers controlling whether a horse is bay, chestnut, or black. This comprehensive review synthesises current knowledge on the molecular mechanisms underlying white spotting phenotypes and their associated health consequences, ranging from benign aesthetic variations to serious developmental and sensory defects. Key findings highlight that whilst many white patterns are purely cosmetic—and economically valuable in breeding programmes—certain mutations carry significant welfare implications, including congenital deafness and the Lethal White Overo condition, which is fatal when inherited in homozygous form. For breeding professionals and veterinarians, understanding the genetic basis of white patterning is essential for making informed decisions about stallion and mare selection, particularly when dealing with predisposition to deafness or other heritable conditions. This work provides the technical framework necessary to move beyond selecting horses purely for visual appeal towards evidence-based breeding that prioritises both aesthetic and health outcomes.
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Practical Takeaways
- •Breeders should be aware that white patterning mutations can carry serious health risks beyond cosmetic value, particularly the lethal Lethal White Overo allele
- •Horses with extensive white markings should be screened for associated conditions such as deafness, which may affect handling, training, and safety
- •Understanding the genetic basis of white patterns helps inform breeding decisions and client education about the potential health implications of selecting for specific coat patterns
Key Findings
- •Over 50 genetic variations have been discovered to cause white patterning in horses, compared to only 2 genetic markers determining base coat color
- •White-causing mutations range from benign aesthetic traits to serious health defects including deafness and lethal developmental disorders
- •Lethal White Overo is a fatal condition occurring when a horse inherits two copies of the allele
- •Genetic complexity of white coat patterns is substantially greater than base color determination