Genomic regions and candidate genes associated with forehead whorl positioning in Thoroughbred horses

Previous studies have examined the relationship between hair characteristics and temperament traits in various animals. A partial genetic association has been suggested in humans because whorl formation and neurological development occur simultaneously during the fetal period. In the horse industry, anecdotal evidence suggests a link between the forehead whorl position and temperament. In our previous study, the heritability of forehead whorl positioning was h²=0.653, indicating significant genetic contributions in thoroughbreds. Therefore, in this study, we designed a genome-wide association study using 192 Thoroughbred horses to detect candidate genes associated with forehead whorl positioning. The results revealed 11 suggestive markers on chromosomes 2, 14, 15, 19, and 26, although no significant markers were found. Five genes, namely PTTG1, CCNH, RASA1, COX7C, and CLDN1, located near these markers had functions related to skin cell or hair follicle development and temperament. Therefore, these genes may be involved in the positioning of the forehead whorl in Thoroughbreds. The candidate genes identified in this study are expected to contribute to elucidating the genetic factors behind forehead whorl in horses and to help interpret the common process of whorl and temperament development.