Thoroughbred racing

Question
Can only thoroughbreds run in races and why did people not want a filly to run in the Belmont stakes. Do only males have the right to runin certain races?

Answer
hi well no  any breed horse can run in races  such as paint horses  mules  quarter horses all run in races  out west. fillies are not usually ruin against the males. it is a sex thing. fillies are usually not as strong as the males so they run fillies against fillies. if the race is for colts an geldings then only males can run in that type of condition race.  fillies do run against the males in rich money races, but not too many times  hope that helps you  thanks ED HESS