The Windfall Lineage’s Thoroughbred Ancestry: Pedigree vs. Genomic Measure

Today, we are taking a look at a line of horses and how drastically different pedigree can be from actual genomic measures of Thoroughbred ancestry. We will further analyze this using the Windfall lineage. Windfall II, owned by Tim Holekamp, is a 27-year-old Trakehner stallion sired by Habicht and out of Wundermaedel, that represented the United States in the 2004 Olympic Games to help secure team bronze. Accumulating 1,281.5 points over his eventing career, Windfall II is third on the list of United States Eventing Association, Inc. (USEA)'s historical high point standings.

Windfall II has two sons that competed at the 2020-21 Tokyo Olympics for Team USA Eventing, the USEF Champion and USEF Reserve Champion: Tsetserleg (Windfall II x Thabana) and Vandiver (Windfall II x Visions of Grandeur)!

We want to take a close look at the horse’s genomic measure of shared Thoroughbred “Blood”, or Ancestry. This is the genetic percentage shared with a reference population of known Thoroughbreds. This measure may differ from pedigree calculations by as much as 30%, which is shocking! But why is that?

Pedigrees provide an approximation of genomic data, calculated based on the idea that every time you breed horses the sire passes on 50% of his genetics and dam passes on 50% of her genetics. However, we know that this isn’t always the case! Because of instances called “recombination events” that occur within reproductive cells, oftentimes two full siblings may have very different Ancestry percentages. This is true for humans as well! Chances are you didn’t get exactly the same 50% of your DNA from your mom and 50% from your dad as your siblings, but a balance somewhere in the middle.

Genomic measure is much more accurate. We can measure genomic data from a horse’s DNA and compare that Ancestry to the Thoroughbred population. Meanwhile, a horse’s pedigree is just a proxy. Before we could measure this value from actual genetics, we relied on pedigrees to make crucial breeding decisions. Now, however, with genetic testing available, pedigree-based analysis of inbreeding and ancestry is quickly becoming “outdated”.

Let’s take a look at Windfall, for example. Based on his pedigree, he should have 84.40% shared Thoroughbred Ancestry. After DNA testing, we see that he actually has much less - only 65.50%. Percent shared Thoroughbred Ancestry may have a real effect on a horse’s performance at various disciplines, especially on the cross-country field. Let us know what inferences you think can be made about a horse’s shared Thoroughbred ancestry in the comments below!

Percent Thoroughbred ancestry data is now available through Etalon’s Ancestry and Composition test. Every horse has a story - know yours down to the DNA with Etalon Diagnostics. #EtalonDx #ShowOffYourGenes