A horse has suffered a "horrendous leg injury" falling over a jump in front of hundreds of spectators at an Easter racing carnival in South Australia.

Wheeler Fortune fell during the running of the Somerled Hurdle race in Oakbank, in the Adelaide Hills, on Saturday, the RSPCA said in statement.

"No one should be surprised that we've had yet another horse killed by this inhumane activity," RSPCA SA's Dr Rebecca Eyers said on Saturday.

"To witness this horse suffering such a catastrophic injury is an image I know I won't forget and I'm sure many others won't either."

The RSPCA says forcing horses to gallop long distances while jumping over obstacles is a "recipe for this kind of tragedy to occur".

"It will keep occurring as long as we continue to allow it," Dr Eyers said.

The five-year-old gelding fell at the last hurdle of the race and was euthanised on the track.

A total of 79 horses have died in Australian jumps races since 2006, 17 in SA since 2009.

South Australia and Victoria are the only states in the nation that haven't banned the sport.