Jockey's have dangerous jobs.  The Australian study quoted in my link found that they have the 2nd most fatalities by percentage of any gig down under.  I'm sure the stats would show a similar trend in the states.

http://sports.yahoo.com/rah/news;_ylt=Ar0nd20fkzTccUQ7stAmAFEX47kF?slug=ap-australia-jockeys

Something I found interesting was that bad spills tend to happen in races with less horses and/or the first race of the day.