Race horses are being pushed beyond their physical limits by the use of whips by jockeys, a welfare group says.

The Coalition for the Protection of Racehorses has called on the racing industry to ban whips following the death of Melbourne Cup pre-race favourite Admire Rakti which collapsed after the event on Tuesday.

"We believe that pushing horses beyond their physical limits through use of the whip, and racing horses while under-developed at two years of age are significant factors as to why horses break down on the racetrack," spokesman Ward Young said.

"We're calling on the racing industry to start running whip free races and phase out two year-old racing."

But Racing Victoria's chief vet Dr Brian Stewart says excessive whipping wasn't a factor in Admire Rakti's death.

He said the organisation reviewed footage of the race and the jockey stopped using the whip when the horse didn't respond.

"The jockey immediately put the whip away and relaxed on the horse to ease distress," he told ABC Radio.

"There's no question in this case that the whip played any role whatsoever."

The CPR group claims 125 horses died on Australian racetracks between August 1 last year and July 31 this year.

"That is one horse being killed every 2.9 days," Mr Young said.

Admire Rakti, a seven-year-old from Japan, is believed to have died of a heart attack.

He had returned to his stall in a distressed state at the Flemington racetrack after running last in the Melbourne Cup.

An autopsy was conducted on Tuesday night at the University of Melbourne and initial results point to acute heart failure.

Dr Stewart said such events were rare.

Another Melbourne Cup runner, Araldo, had to be put down on Tuesday after breaking his leg when he was spooked by a racegoer waving a flag following the race.

The RSPCA said the outcome for both horses was tragic and there should be a full investigation into the separate incidents.

"Sadly, injury and death are the price some horses pay for our entertainment in a sport that puts intense pressure on animals to perform to the limits of their endurance," it said in a statement.