In response to my article on Horse Racing Nation about the durability of Unbridled's Song's offspring, people mentioned Mr. Prospector and Big Brown as two other sires whose offspring might be expected to show signs of unsoundness. My data on both is limited, but I took a look anyway.
Mr. Prospector's offspring showed an average of ten career starts. That certainly suggests some issues, but may also be due to very limited sample size (less than 100 horses) in my database.
Big Brown's offspring so far are averaging eleven career starts. That sounds bad, but it's actually pretty average for two reasons:
1. I believe his first crop is only six years old now. So a very large percentage of his offspring who have raced have not yet finished their careers.
2. Other sires who began their stud careers in the 2007-2009 time period are showing similar averages. This may partly be due to the factor in #1 above, and also may reflect the tendency for horses to race less than they did even 10-20 years ago.