Are the Offspring of Unbridled’s Song Really Unsound?

One of the great things about data analysis is that we often find that the truth is far different from what we’ve been led to believe. Many commonly believed ‘facts’ turn out to be false when we attempt to verify them. There’s been a lot of discussion about whether Unbridled’s Song has a tendency to pass on his unsoundness to his offspring.

With the dominant win of Arrogate in the Travers, debate on this topic has, once again, become a popular topic of conversation in the thoroughbred racing community.  I have to confess that I’ve always assumed that this belief was based on a few anecdotal, well-known examples and would be proven to be nonsense by any rigorous analysis.

It’s always satisfying to disprove a commonly held belief. With that in mind, I recently decided to look at the durability of Unbridled’s Song’s offspring to answer the question once and for all. It turns out that I was in for a surprise!

Excluding those that never made it to the racetrack, the average American thoroughbred this millennium has made approximately sixteen starts in their career. Unbridled’s Song has had over one thousand offspring who raced in the U.S. and those horses have only averaged eleven starts in their career. That’s a drastic difference.

I was concerned that perhaps the numbers are different for offspring of top sires than for the thoroughbred population as a whole. Their children may tend to be retired earlier due to their breeding value or trainers may handle their racing careers differently. To control for this effect, I narrowed my analysis to the top one hundred sires ranked by total number of starters (since 2000). Among the other ninety nine horses, only one of them averaged less than twelve starts per horse.  This seems like a very clear indication that the offspring of Unbridled’s Song really do tend to be less durable than those of other top sires.

Interestingly, the other apparently ‘unsound’ sire is one that you may have heard: Storm Cat. I haven’t dug into it yet, but suspect that his average may be lowered by a disproportionate number of turf horses whose careers included races overseas, which aren’t included in my database. I also suspect that any tendency for offspring to be retired early for breeding would be stronger for Storm Cat than any other stallion in the sample.  As a result, I’m not as confident that the data is pointing to soundness issues for his offspring as I am for Unbridled’s Song.