Frequency of gray coat color in native Chinese horse breeds.

Gray horses are born colored, and they then gradually lose their hair pigmentation. Tremendous progress has been made in identifying the genes responsible for graying with age in horses in recent years. Results show that gray coat color in horses is caused by a 4.6-kb duplication in intron 6 of the syntaxin 17 gene (STX17), which constitutes a cis-acting-regulatory mutation. However, little is known about the gray phenotype in native Chinese horses. This study was conducted to explore the frequency distribution of the gray mutation in native Chinese horse breeds. A total of 489 samples from 14 native Chinese horse breeds were genotyped for the STX17 duplication using a simplified conventional PCR-based method. The results show that the gray mutation was present in 12 native Chinese horse breeds, except the Balikun and Guanzhong breeds. The Chakouyi and Hequ breeds had the highest frequency of the gray mutation (P(G) = 0.367 and P(G) = 0.274, respectively). There was no significant geographical difference in the distribution of gray coat color across native Chinese horse breeds. Our results suggest that gray is a common coat color in Chinese horses.