PSIV-26 Tracing changes in coat color phenotype over time within the Mountain Pleasure Horse Association.

Abstract The Mountain Pleasure Horse (MPH) is an American gaited horse breed that has a limited population of under 3,000 horses. Due to limited size, there’s a misunderstanding concerning the breed with it often confused for the Rocky Mountain Horse (RMH), another popular American gaited horse breed. Besides gaits, a distinction between the breeds is the coat color phenotype as the MPH is typically known to have a palomino coat color compared to RMH’s chocolate coat color. However, registration guidelines have become less restrictive in recent years to expand the MPH population. This change in registration may impact phenotypical characteristics such as coat color; thus, to evaluate changes within the registry concerning coat color phenotype, the objective of this study was to utilize pedigree tracing to identify coat color variations over time for purebred horses registered within the MPH Association (MPHA). A total of 2,255 pedigrees were sampled from the MPHA database. Only purebred horse records with coat color assignments and date of birth were utilized for this study. For comparisons, records that met this inclusion criteria were divided between the first two decades of registrations within the database (1960-1980, n=98) and the last two decades (1990-2010, n=708). While the two most common coat colors within the first two decades were either palomino (26.5%) or chestnut (26.5%), for the last two decades evaluated, the two most common coat colors were either chestnut (30.2%) or chocolate (20.9%). Palomino registrations had the largest drop in numbers with a 10.4% decrease in registrations. Black, brown, and roan coat colors similarly decreased in registrations by 1.0%, 0.9%, and 1.1%, respectively. Champagne, dun, and cremello were not coat colors found within the first two decades of the database, but each coat color phenotype was present within the last two decades, increasing in registrations by 0.1%, 0.1%, and 0.4%, respectively. Understanding trends over time within registrations can assist in determining knowledgeable breeding practices that can assist in preserving desired phenotypical characteristics within a horse breed. This is of particular value among breeds such as the MPH that have smaller populations where genetic diversity is crucial for breed sustainability.