An undercover investigation revealed covert video footage of the animals allegedly being beaten and electrocuted at an abattoir in Queensland.
The footage, aired on ABC’s 7.30pm programme on Thursday, sparked an outcry and prompted the government to launch an investigation into the allegations.
The slaughter of racehorses is not illegal in Australia – however industry rules in some states, including New South Wales, which was also a focus of the ABC investigation, require horses to be rehomed.
Paul McGreevy, a vet and professor of animal behaviour and welfare science, who has been studying thoroughbreds for 25 years, told ABC: "We're talking about destroying animals on an industrial scale. We're seeing animals suffering.”
About 8,500 horses retire from the racing industry each year – and according to the industry, less than one per cent end up in a knackery or abattoir.
However, Elio Celotto and the Coalition for the Protection of Racehorses have been watching an abattoir in Queensland for two years and they tell a different story.
According to the report, the coalition found the abattoir slaughters mixed livestock, including about 500 horses a month.
A team of undercover investigators also entered the slaughterhouse, where they recorded a thousand hours of footage which showed brandings on the horses and also scanned their microchips.
ABC cross-referenced the information with the Australian Stud Book, an official online record of thoroughbreds, and found 300 racehorses were processed through the abattoir within a 22-day period.
Some of the meat was allegedly found to be exported to Europe and Japan for human consumption.
Professor McGreevy told ABC: “The industry tells us that 0.4 per cent of horses leaving the racing industry are ending up in a knackery or an abattoir, which I think equates to 34 horses per year.
"The figures don't add up.”
Kevin Anderson, New South Wales racing minister, said the ABC report would make people in the industry “sick to their stomachs”.
The head of Racing Australia said it “should” and “likely will” lead to prosecutions.
However, the national body admitted it did not have the ability to track every racehorse after retirement and once again called for a national traceability register.