Anti-jump racing protestors jumped the fence when Slowpoke Rodriguez lay motionless on the turf after a horrific fall.
Trainer Patrick Payne rushed to the horse's side as vets came to the scene.
The horse was later led away and appeared to be fine. The coalition for the protection of racehorses spokesman Elio Celotto said there were a number of falls at the event on Saturday.
“There were six races on the card yesterday and it was inevitable that we would see some falls,” Mr Celotto said.
“We saw several horses being pulled up – while on one hand it is good to see that organisers are trying to reduce number of incidences, on the other hand it highlights the extreme pressure these horses are under.
“Even though these horses may complete the race, it doesn’t mean they won’t sustain injuries.”
Mr Celotto said many of the horses in yesterday’s race may not be seen again because of the injuries they sustained.
“The racing industries needs to consider a complete ban on jumps racing,” Mr Celotto.
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