Ever since Archer won the inaugural Melbourne Cup, the race that stops the nation has been surrounded by controversy.

The first event on November 7, 1861, at Flemington saw three of the 17 starters fall during the race. Two of them died, two jockeys suffered broken bones and one horse bolted off the course, but the race continued.

Fast forward to 2018 and the cup has taken another victim.

The Cliffsofmoher became the sixth horse to die as a result of the race since 2013. That year Verema's death was much quieter because the French mare did not finish.

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A year later two horses died. Admire Rakti collapsed and died in his stall after the race, and Araldo broke his right hind leg and had to be euthanased.

In 2015 Red Cadeaux lay on the ground with a shattered leg. He was euthanised about two weeks later after vets decided they couldn't fix it.

Last year, Regal Monarch broke his right leg and had to be euthanised.

That's because it's difficult to heal a horse's fracture.

Horses can go on to develop laminitis, an inflammation of the foot that is extremely painful and causes instability.

Celebrity vet Dr Chris Brown said if forces came from a strange angle or a stress fracture was already present, the bone did not just gently break, it tragically exploded.

"Multiple, misshapen bone fragments are then left behind," he said.

"Fragments that then can't be pinned or plated back into place.

"The other issue is rest. Unlike a dog or cat, horses struggle to cope on three legs while one is mending. Nor can they lie down or be suspended on slings.

"That big body of theirs becomes susceptible to circulation problems and pressure sores if they're doing anything but standing on all four legs with their weight evenly supported."

Back in 1979, Dulcify courageously ran a kilometre of the race with a broken pelvis.

Vets recommended immediate euthanasia but his champion trainer wasn't ready to give up and wanted to give the horse every chance of survival.

Dulcify was taken to his stables at the back of the track to be inspected by the trainer's vet but he rapidly came to the same conclusion as the broken bones of the shattered pelvis had damaged internal organs.

Dulcify was put down at 5.40pm on November 6, 1979.

But the Melbourne Cup isn't the only race with casualties.

From July 2016 until July 2017, 137 horses died on Australian racetracks.

Tuesday's death understandably sparked outrage.

"6 in 6 years. That's absolutely disgusting. Too many horses in one race. It's not safe for them when they get all bunched up. One step on another horses leg and they are put down," wrote one person on Twitter.

PETA has called for an investigation into the death of The Cliffsofmoher.

The animal rights organisation said before they had even finished maturing, the 500kg animals were forced to race at breakneck speeds while being whipped and pushed past their limits, supported on ankles as small as those of humans.

World Animal Protection also condemned the incident, labelling the Melbourne Cup a "disgrace".

"The Melbourne Cup is the disgrace that stops a nation. It's heartbreaking to see another horse needlessly lose its life during the Melbourne Cup," senior campaign manager Ben Pearson said in a statement.

"World Animal Protection opposes the use of all animals in entertainment, including the use of horses in the racing industry. It's time to end the cruelty."

But others have highlighted the other side of the story.

In 2016 Dr Natasha Hamilton wrote an opinion piece for the University of Sydney highlighting the myths perpetuated.

She said one of the most common myths was horses were only bred for money and were put down because it cost too much to treat them.

But Dr Hamilton said it costs on average $70,000 to buy a racehorse, and between $30,000 to $50,000 per year to train it.

However, 63 per cent of horses that race will earn less than $10,000 each year, and less than 3 per cent will make $100,000 a year to cover their costs.

"Horses are euthanised on the track [or later in hospital after diagnostic imaging] because they are unable to recover from these injuries," she said.

"The reasons for this apply to all horses that break their legs, not just racehorses.

"The good news is that with advances in research and veterinary medicine, catastrophic injury rates will decrease over time.

"No one cares more for racehorses than those who care for them on a daily basis."

Others on social media are of the same thought.

"People who say ban it really get my back up, do we ban people from driving cars? Or ban surfing? Maybe we should ban walking to people die every day. Time to move on."