Personally I would like to see all horses race as 4 year olds but I understand why owners of those that have potential in the breeding shed want to shut them down at 3. Is it that they are trained and raced too hard at two and three and the potential is too high for them to look bad at four becuase they are all nursing nagging lameness issues.Are the tracks too hard creating curbs and legiment and hoof problems.There are no answers to many of these questions but it seems the norm for the to quit at 3.