The risk of elevating a horse race from a niche sporting event to a national symbol is that, when the nation changes, so too must the event.

This is the challenge facing the organisers of the Melbourne Cup, who are torn between upholding the traditions of an inherently conservative sport and attempting to maintain their hold on the public consciousness despite pockets of outrage and a growing sense of indifference.

Recent footage of racehorses ending their careers at the slaughterhouse may prove a tipping point for what has become an event that some now see as no less outdated and exploitative as a circus with elephants.

University of Sydney professor Carole Cusack, who wrote in 2009 that attending the Melbourne Cup at Flemington was one of Australia’s secular pilgrimages, said she once considered the first Tuesday in November to be the one “relatively unproblematic” entry in Australia’s triptych of national days, which includes Australia Day and Anzac Day.

Increasing concern about the welfare of retired horses and a string of deaths on the track – six horses have died during or as a result of the Melbourne Cup since 2013 – have changed that.

“It is no longer relatively unproblematic,” Cusack said.

Anecdotal evidence suggests the tide may be turning among a broader public. Dozens of people Guardian Australia spoke to – many previously neutral or mildly positive towards the race – say they plan to boycott the office sweep this year. Others say they were already appalled by the cultural cringe of seeing dozens of well-dressed adults vomiting into port-a-loos at 2pm, describing the spectacle of horse racing as both insufferably stuffy and unbearably gauche.

Six horses have died during or as a result of the Melbourne Cup since 2013. Photograph: Vince Caligiuri/Getty Images

Some who have attended a spring carnival event in Melbourne as a way to see friends each year say they will not return until the industry submits to independent, robust regulation, rather than opaque industry-led promises to ensure spent thoroughbreds are retired to new homes.

They have asked how to balance their growing unease with the memory of their teetotaling grandmother placing a bet each way for her grandchildren.

“Should I tell my dying father, keen to make a few lasting memories with his family that I could no longer support the sport, or should I just humour him and my mother?” one woman wrote. “How could I be true to my need to support ethical treatment of animals yet respect my family’s traditions?”

The headline act, Taylor Swift, pulled out in September following a campaign by fans urging her not to support it for animal welfare reasons, to be replaced by 2004 Australian Idol runner-up Anthony Callea. Callea has pledged to donate his performance fee to a horse welfare charity. Supermodel Megan Gale, a fixture of the cup carnival for the past decade and brand ambassador for the race’s major sponsor, Lexus, says she won’t attend because of animal cruelty concerns. Some companies have cancelled their annual Melbourne Cup lunch.

Even the bookies are worried, reportedly saying it will be “too hard to make money this year” with betters more interested in other sports.

If the Melbourne Cup were just a horse race, it would not generate this level of national angst. But “the race that stops the nation” had loftier goals, embedding itself in the national identity.

‘A particular version of Australian-ness’

The Melbourne Cup was first run in 1861 to a crowd of 4,000 people. Two horses died. It was a handicap race with a broad field and sneered at by the self-appointed arbiters of the Australian Jockey Club, whose premier event, the Sydney Derby, was a fixed-weight race designed to identify the best three-year-old colt in any given year.

The Melbourne Cup, by contrast, was anyone’s game. Good horses were made to carry a substantial amount of extra weight, while the bottom end of the field, carrying the lightest weights and the longest odds, had a better chance.

It suited the high-risk, high-reward culture of Victoria at the tail end of the gold rush, says historian Richard Waterhouse (no relation to the Waterhouse racing dynasty).

“You could make huge amounts of money and then you could lose huge amounts of money, and the Melbourne Cup reflected that ethos,” he says. “It didn’t mean the best horse won.”

There is a tension between those who love the horses and the necessity to be absolutely brutal in the way you conduct your business. Historian Richard Waterhouse

That made it more popular with the public than a breeder’s race, says racing historian Wayne Peake, who says the handicap format appealed to Australia’s egalitarian values.

Paired with the other pillars of colonial Australian entertainment – gambling and drinking – it soon became the highlight of the social calendar.

“The fact that at the Melbourne Cup, you could win a lot of money for a small outlay obviously popularised it with the people,” Peake says. “[It] took the racing into very much a gaming proposition, not just a matter for the squattocracy to race against each other for small stakes in set weight races.”

By the end of the 19th century, a quarter of Melbourne watched the race. In 1895, Mark Twain visited Melbourne and reported himself overwhelmed.

“Nowhere in the world have I encountered a festival of people that has such a magnificent appeal to the whole nation,” Twain wrote. “The Cup astonishes me.”

In 1930, Phar Lap arrived at the track under police guard following a suspected assassination attempt. His death from arsenic poisoning in the United States in 1932 turned the animal celebrity into something resembling a deity, his remains split between three museums. More than 540,000 visited his body at the Melbourne museum last year.

The cup came to represent “a certain kind of Australian-ness”, says Prof Fiona Nicoll, a gambling policy expert who has researched the Melbourne Cup.

It was an “Australian-ness” defined in the era of the White Australia policy, Nicoll says. Racing played into both the celebration of Anglo-Saxon heritage and broader narratives around purity of blood, which were used to justify the removal of Indigenous children.

It was “a story about Australia that doesn’t take account of the people who were here before the whites came and also doesn’t stretch out to be particularly inclusive towards the people who came after the white story was established”, Cusack says.

Phar Lap, the most famous Melbourne Cup winner. Photograph: State Library Victoria

Racing’s relevance has decreased with every year since the white Australia policy was abolished in 1966. Increasing multiculturalism, Peake says, is one of the reasons behind its waning popularity.

He also attributes it to a push from the Victorian Racing Club to attract more international runners in the cup, suppressing the handicap weights and decreasing the chance of a long-odds Australian-bred horse roaring to victory.

But Peake says that to claim racing has reached the end of its social licence is to ignore the work done by the industry, who are “all genuine horse lovers,” to improve equine welfare. He says those efforts should receive more publicity.

“Racing is strong; racing is resilient,” Peake says. “It will need to come to terms with some of the shortcomings that have been exposed, but it will. Don’t dismiss horse racing, there’s a lot of people power in horse racing as well as the animal rights activists.”

‘A ruthless sport’

Waterhouse spent several years at racetracks writing the official history of the Australian Jockey Club, but has not been back since it was published in 1992. As of this year, he says, “I feel quite strongly that I will not support the racing industry, unless it does something about providing for retired thoroughbreds.

“I met a lot of people who told me about their love of horses … that they really, really loved horses and they are in horse racing for the love of horses,” he says. “But horse racing in Australia, as elsewhere, is an incredibly ruthless sport.”

Most people in racing operate on very small margins, and the outrageous success of a very few is outweighed by the many who are barely scraping by. Some wealthy racehorse owners “can afford to be kind”, Waterhouse says. Most cannot.

“There is a tension between those who love the horses and the necessity to be absolutely brutal in the way you conduct your business to succeed at all levels,” he says.

Footage broadcast on the ABC last month of racehorses being slaughtered at a Queensland abattoir was brutal, unavoidable proof of a well-known but rarely discussed fact of life in both thoroughbred and standardbred racing.

It is a well-worn debate. On the morning after the 1979 cup, then 3AW radio broadcaster Derryn Hinch informed his listeners that cup favourite Dulcify, who had entered the race with the shortest odds since Phar Lap won in 1930, had been turned into chicken feed. He had won the Cox Plate by seven lengths the week before.

Dulcify broke his hip 400m from the finishing post and was taken to the Melbourne stables of his distraught trainer, Colin Hayes, to be euthanised by a vet in the back of the horse float. His body was offloaded into an empty pen of the Newmarket sale yards and covered with leaves by members of Hayes’s staff, who were worried he would be recognised.

Hinch stuck by his sources that Dulcify had been converted to chicken food, despite Hayes angrily saying that the “best horse he had ever raced” had been buried on a friend’s farm. The truth remains contested.

Jockey Aiden O’Brien with The CliffsofMoher after the horse was injured in last year’s Melbourne Cup. It subsequently had to be euthanised on the track. Photograph: Dan Himbrechts/AAP

The fate of ex-racehorses is the driving force behind the Coalition for the Protection of Racehorses. Its founder, Elio Celotto, conducted his first protest with a handful of friends in a three-metre square tent on a hill outside Flemington in 2011. This year, he is expecting “hundreds” to attend.

“As people are becoming more aware of the cruelty, people are turning away from horse racing,” Celotto says. “Some people who are our supporters now rang me up directly years ago and abused me for trying to end horse racing … there are people that love going to the races and are not going any more.”

Celotto says the high-profile deaths of horses during the cup, such as the Irish stallion The Cliffsofmoher, euthanised in front of the grandstand last year, has focused attention on the sport. His group has compiled stewards’ reports showing that 122 horses died on Australian racetracks from August 2018 to July 2019, and says the fate of horses off the track – the foals that do not make it, broodmares discarded through sales and retired racehorses bought by kill buyers – is worse.

Traditional media is heavily enmeshed with horse racing, but on social media the potential for animal abuse is slowly overtaking glossy glamour shots in coverage of the day.

Or, as one regular better told Guardian Australia: “I just don’t think that the frequency of deaths is an acceptable trade-off so that we can have fun gambling.”