The running of the Melbourne Cup has again been marred after one of the 2018 entries in the race, The Cliffsofmoher, was euthanised at Flemington Racecourse – the sixth horse to suffer that fate since 2013.

The Irish stallion, trained by Aiden O’Brien for Lloyd Williams, pulled up inside the first 600m after suffering a fractured shoulder. He was unable to be saved and was put down at the track.

“The chairmen and directors of the Victoria Racing Club extend their sympathies to the Williams family and the connections of The Cliffsofmoher, which was euthanised after he went amiss in the Melbourne Cup,” a VRC statement read.

The five-year-old, ridden by the English jockey Ryan Moore, joins Verema, Admire Rakti, Araldo, Red Cadeaux and Regal Monarch in having died during the Melbourne Cup in recent years.

The RSPCA said the tragedy “highlights the very real risks to horses from racing”.

The animal rights organisation PETA Australia claims 119 horses died on Australian tracks between August 2017 and July 2018, an average of one death every three days.

PETA called for an investigation into the death of Cliffsofmoher and requested the Cup public holiday be cancelled and replaced with a day “more in line with animal loving Australians’ values”.

Horses are usually put down after sustaining injuries that would not normally pose a threat to a human life. There are a number of reasons for this, chiefly because they are unable to recover.

Horses have lighter bone mass and, when a break occurs, the bone shatters, making it difficult to repair. Even if the bone does mend, there is a risk the bone will be deformed and will be unable to bear weight – and the horse is likely to suffer severe pain.

Moore was unhurt.

That’s the other thing of course, thoroughbred racing is a sport of children. Cliffsofmoher was a four-year-old. Barely an adult body. — Jonathan Green (@GreenJ) November 6, 2018

Getting increasingly hard to "enjoy" the #MelbourneCup when some poor horse seems to lose its life every year. RIP sweet angel #cliffsofmoher 🦄 No longer a victim of man's greed. 😥 — jeanvb (@jean_virginia) November 6, 2018

Jamie Stier, Racing Victoria’s manager of integrity services, said the horse had received immediate veterinary care on the track but it was unable to be saved.

“This was an unfortunate incident that happens infrequently, with Victoria having one of the best safety records in world racing,” he said.

“Our sympathies are extended to Coolmore and the Williams family, the owners of The Cliffsofmoher, jockey Ryan Moore, trainer Aidan O’Brien and his staff who cared for the horse and are greatly saddened by their loss.”