Rising trends of inbreeding in Japanese Thoroughbred horses.

The research article explores the heightened levels of inbreeding in Japanese Thoroughbred horses, particularly over the past three decades, highlighting the influence of two pedigree lines from Northern Dancer and Sunday Silence stallions.

Research Background and Objectives

• The research investigates the increasing trend of inbreeding within Japanese Thoroughbred horses, focusing on the changes that have happened over the past 46 years.
• This research aims to identify the key contributing factors behind the rise in inbreeding and the related consequences it could bring to the Thoroughbred horse population.
• It particularly centers upon the impact of two significant stallions, Northern Dancer and Sunday Silence, on this inbreeding trend.

Key Findings

• The study revealed a noticeable increase in inbreeding within the researched period, specifically within the last 30 years.
• Two primary sources for the increased inbreeding trend were identified: Northern Dancer and Sunday Silence, both of which significantly influenced the Thoroughbred horse gene pool.
• Northern Dancer’s genes disseminated gradually via offspring, such as Northern Taste, leading to a slower but steady rise in inbreeding levels.
• Contrarily, Sunday Silence, imported directly, quickly became a leading sire, contributing to a sharp increase in the proportion of his bloodline and inbreeding coefficient within the population.

Implications of the Study

• The results from this study advise that the history of successful sires should be closely tracked and historical factors vicariously taken into account, to help predict and manage potential risks of inbreeding depression in future Thoroughbred populations.
• It also highlights the importance of limiting the influence of a limited number of sires for maintaining the genetic diversity within the Thoroughbred horse population and preventing inbreeding depression.