Murray State University
Pedigree Analysis to Determine the Mode of Inheritance of White Markings in the Norwegian Fjord Horse
Institution
Murray State University
Faculty Advisor/ Mentor
Everett Weber
Abstract
Many breeds of horses have common white markings on their head or lower legs. Such areas of depigmentation are predisposing factors for ailments, including squamous cell carcinoma, equine pastern dermatitis, and photosensitization. Previous studies concluded white markings have a multifactorial mode of inheritance; however, the studies were conducted on breeds that permit crossbreeding. Our study used a breed that strictly prohibits crossbreeding, the Norwegian Fjord Horse. The Fjord is a breed in which white markings are highly discouraged, resulting in underreporting and selection against horses with white markings. The Fjord Horse community also believes that white markings are a recessive trait, affecting breeding decisions. Through pedigree analysis of survey data, we have eliminated the possibility of simple dominance as a mode of inheritance. In addition, preliminary data suggest that the inheritance is not simple recessive either. We do not currently have enough data to negate or support the multifactorial or incomplete penetrance inheritance patterns. Our pedigree analysis also indicates that breeders select against white markings in stallions but not mares. Combined with the variable expression of this trait, this form of selection is not likely to successfully remove the white marking trait from the Fjord Horse population. Further research includes expanding our database to include tests for the KIT gene, which has been shown in other horse breeds to be responsible for white markings. Horse breeders can use our research on the mode of inheritance to make informed breeding decisions and thereby remove this potentially harmful trait from the Fjord Horse population.
Pedigree Analysis to Determine the Mode of Inheritance of White Markings in the Norwegian Fjord Horse
Many breeds of horses have common white markings on their head or lower legs. Such areas of depigmentation are predisposing factors for ailments, including squamous cell carcinoma, equine pastern dermatitis, and photosensitization. Previous studies concluded white markings have a multifactorial mode of inheritance; however, the studies were conducted on breeds that permit crossbreeding. Our study used a breed that strictly prohibits crossbreeding, the Norwegian Fjord Horse. The Fjord is a breed in which white markings are highly discouraged, resulting in underreporting and selection against horses with white markings. The Fjord Horse community also believes that white markings are a recessive trait, affecting breeding decisions. Through pedigree analysis of survey data, we have eliminated the possibility of simple dominance as a mode of inheritance. In addition, preliminary data suggest that the inheritance is not simple recessive either. We do not currently have enough data to negate or support the multifactorial or incomplete penetrance inheritance patterns. Our pedigree analysis also indicates that breeders select against white markings in stallions but not mares. Combined with the variable expression of this trait, this form of selection is not likely to successfully remove the white marking trait from the Fjord Horse population. Further research includes expanding our database to include tests for the KIT gene, which has been shown in other horse breeds to be responsible for white markings. Horse breeders can use our research on the mode of inheritance to make informed breeding decisions and thereby remove this potentially harmful trait from the Fjord Horse population.