By Byron Rogers
- Of all the domesticated breeds, the Thoroughbred's lineage is by far the best recorded and most accurately detailed. It is a great testament to the American Stud Book, The Jockey Club, and the industry itself that we do have such records available to us to evaluate, purchase, and breed Thoroughbreds based on their pedigrees and the performance of their ancestors. It is something we have a right to be proud of.
That all said, pedigree historians have long questioned, and rumors have often persisted, about the accuracy of pedigrees within the breed. If you are in the industry long enough, you hear the old stories about foals by certain sires and out of certain mares where the parentage is suggested to be dubious at best. That is not to mention much of the early history of the breed where accurate records were lost and mistakes were made in the initial compiling of both the General Stud Book and American Stud Book.
On March 17, Dr. Stephen Harrison of Thoroughbred Genetics in England released a peer reviewed study on mitochondrial DNA (mtDNA), the DNA strand that travels along the female line (it goes to a son but he doesn't pass it on) from generation to generation. It was a study that, in part, covered issues relating to the integrity of the breed.
Dr. Harrison's work covered 1,000 Thoroughbreds that traced down their female line, daughter to mother, from 33 different female families. Of those 33 families, 19 families had individuals whose mtDNA was in disagreement with the General Stud Book's recorded lineage of the individual. With questions to be answered regarding mutation of Thoroughbred mtDNA, it appears that somewhere along the line the mtDNA does not match with what we have recorded.
The mtDNA study that Dr. Harrison undertook follows a similar study by Drs. Emmeline Hill and Patrick Cunningham from Trinity College in Ireland, of just 100 mares, that also found similar inconsistencies. There is a third mtDNA study currently being undertaken here in North America by Dr. Phillip Danielson, a professor of molecular biology at the University of Denver, and Loren Bollinger, a breeder in New Mexico. Under the scrutiny of a world-class forensic laboratory, their study has also found mtDNA disagreement with recorded lineage.
It is easy to dismiss the findings as something that happened a long time ago and whose relevance only applies to a few pedigree enthusiasts around the world, to whom known ancestry holds importance. We can only wish it were that simple. It is true that in the main the errors seem to point to less than accurate record keeping in the late 1800s or earlier, but according to Dr. Harrison there are examples of horses born as late as 1973 where the horse, based on its mtDNA, does not appear to be out of the mare that has been recorded in the General Stud Book.
As all stud books around the world germinated in some form from the General Stud Book, the errors that began there have replicated. Add to this further errors created in each country up until blood typing and DNA testing began, and with the proliferation of the breed, it is hard not to believe that if one looked at the whole pedigree of a horse it is now nearly impossible to find a Thoroughbred that does not have an error in its lineage somewhere. All of this is unsurprising when up until recently we were relying on an honor system to verify parentage, but thankfully, since the introduction of DNA testing by The Jockey Club in 2001, these types of errors are a matter of history.
The Thoroughbred horse is a unique creation of mankind that has been selectively bred for a single purpose for almost 350 years. Its recorded lineage, should be as accurate as possible. The matter of correcting the record is a considerable task whose cost effectiveness and ultimate outcome will be debated, but environmental and biological influences aside, any sort of reasonable attempt at breed improvement through selective mating depends primarily on accurate lineages, as incorrect lineages only increase the unpredictability and variability of results.
If we have the technology available to us to make improvements to the record, and by doing so improve what we breed in the future, we should invest in that future.