Presence of a Deletion Mutation of Myostatin ( <i>MSTN</i> ) Gene Associated With Double‐Muscling Phenotype in Japanese Black Cattle Population

Mutations in the bovine myostatin (MSTN) gene have been identified as the causative factor for the double-muscling phenotype in several European cattle breeds, including Belgian Blue, Piedmontese, and Shorthorn. In Japan, following the Meiji Restoration, several European breeds, including Shorthorn, Brown Swiss, Devon, Simmental, and Ayrshire, were introduced and crossbred with native cattle to develop modern Japanese beef cattle breeds, such as Japanese Black cattle. Historical records regarding the breeding of Japanese Black cattle indicate that the double-muscling phenotype, referred to as "Butajiri," occasionally appeared in Japanese Black cattle population. These historical observations suggest the potential presence of MSTN gene mutation in the Japanese Black cattle population. The aim of this study was, therefore, to investigate the presence of MSTN gene mutation in the current Japanese Black cattle population. Through screening 400 reproductive females, we identified one cow carrying an 11-bp deletion in the MSTN gene. While further investigation of the animals in the pedigree of this cow could not reveal any living animals with this mutation, this is the first report demonstrating the presence of the MSTN mutation in the Japanese Black cattle population.