Andrew Beyer addresses the rash of breakdowns at Del Mar and Arlington. He rejects #1 (racing surface) and agrees with #2 (trainers) and #3 (breeders) from my earlier post on the subject. He also believes that the claiming structure contributes to problem:  

The very nature of claiming races almost guarantees that horses with physical problems won't get proper care. Trainers with large-scale claiming operations dominate almost every major track, Del Mar included. The harsh economics of the business dictates the way they manage their horses. When an animal develops physical problems, the trainer is more likely to give him a shot of cortisone as a short-term fix than to give him a rest. When the problems get worse, the trainer will continue to race the horse and drop him in class, hoping that somebody else will claim him and inherit the problems.