Pedigree tracing to determine coat color phenotype found within the Mountain Pleasure Horse Breed

The Mountain Pleasure Horse (MPH) is classified as “threatened,” with only 2,670 living purebred MPHs. To expand numbers, the registration books for MPH Association (MPHA) were opened in 2009; however, the books were recently closed due to concerns of potential loss of breed phenotypic characteristics. Although MPHA registration does not require a specific coat color, the palomino color is a characteristic of the foundation sires, setting the breed apart from the chocolate color of the Rocky Mountain Horse. As such, to determine whether there is a predominant breed coat color phenotype, the objective of this study was to use pedigree tracing to identify the phenotypic coat color assignments making up the MPHA. Using the MPHA database, a total of 1,410 pedigrees of purebred registered horses were sampled (53% of all living purebred MPHs). For purebred designation, genealogy must show 100% MPH bloodlines for 2 generations along with either DNA testing or blood-typing to prove parentage. Pedigrees used were those with complete records, meaning an uninterrupted generational record of the horse's ancestors and associated coat color assignments going to the earliest existing recorded relative. Coat color assignments were documented for each pedigree sampled with percentages determined for the 11 coat color assignments of MPHA. The reported phenotypes were consistent with the following 4 dilution alleles: cream, champagne, silver, and dun. Coat color assignments within 21.3% of the sampled horses were reflective of the cream dilution allele, including 16.4% of sampled horses designated as palomino (Table 1). Coat color assignment for 16.9% of the sampled horses was chocolate, reflective of the silver dilution allele. The most common coat color assignment was chestnut. Interestingly, for those reporting phenotype consistent of the roan allele, 1.8% of the sampled horses were designated as a red roan, thus having a chestnut base coat, with the remainder designated as blue roan (1.2%) or only assigned as roan (0.6%). In closing, the sampled pedigrees do not reflect that MPHA coat color assignments are predominantly palomino; however, responsible breeding practices could facilitate a larger population of purebred MPHs with the palomino coat color.