Regarding 8 Belles:
"While tests have shown that the filly was not racing with steroids in her system, Schakowsky traced the filly’s genetic background, citing examples of fragility within the family that may have contributed to the tragedy."
http://news.bloodhorse.com/article/45791.htm
I can see this now. Congress - "We now declare Unbridled's Song uneligible to reproduce........as well as all sires that throw fragile offspring"