Thoroughbred Pedigrees Show Little Genetic Diversity -- But Less Inbred Than Other Livestock

An older article from TheHorse.com came up in a Google search recently, one published before I began working for the magazine.  The title was intriguing, so I took a look:  Thoroughbred Pedigrees Show Little Genetic Diversity. 

The subject of the article is interesting, but my favorite line has to be a pun: "The superiority of the Darley Arabian has been increasing for nearly 200 years, eclipsing the contributions of the other two foundation stallions, the Byerley Turk and the Godolphin Arabian."  Now, we all know that the Darley male line runs exclusively through the great Eclipse. That stallion's on-track prowess was so dominant that the verb "to eclipse" means "to surpass," and came to signify overwhelming superiority.  So the Darley Arabian truly "eclipsed" the Byerly Turk and Godolphin Barb in tail-mail descent!

But the premise of the article is one that I find fascinating.  I am a proponent of selective inbreeding in Thoroughbreds, and I do not subscribe to the idea that it is inbreeding in general that has caused myriad problems in the breed. (Detractors blame inbreeding for loss of durability, temperament issues, and various health problems in Thoroughbreds.)  As the author points out, most other livestock today is significantly more inbred than Thoroughbred race horses. 

By all means, breeders must be careful when making mating decisions that involve duplication of bloodlines -- but it was patterns of inbreeding that created the Thoroughbred to begin with, and has continued to improve the breed's performance for 300+ years.  Too much is bad, but I submit that too little is counter-productive.

For those of you who are interested in Thoroughbred inbreeding... in addition to the "Thoroughbred pedigrees" article, I suggest a Wall Street Journal piece that looks specifically at inbreeding and the dominance of Native Dancer blood in the modern Thoroughbred horse.