Melbourne Cup-winning trainer Darren Weir has been arrested along with two others during a police raid of his Victorian stables where a gun and taser were seized.
Victoria Police and Racing Victoria raided stables at Miners Rest and Warrnambool from 6am on Wednesday.
Three people have been arrested including Weir, 48, a 38-year-old Yangery man and a 26-year-old Warrnambool man.
"They will now be interviewed in relation to sporting integrity matters," a Victoria Police statement read.
Those matters include obtaining financial advantage by deception, engaging in conduct that corrupts a betting outcome and use of corrupt conduct information for betting purposes.
The force said several items were seized including a firearm and conductive energy device (Taser).
Racing Victoria said it had been investigating "the activities of licensed persons" and brought in Victoria Police.
"During the course of our investigation, we sought the support of Victoria Police's sporting integrity intelligence unit on the matter, instigating their investigation," executive general manager of integrity Jamie Stier said in a statement.
"As the matters are the subject of on-going investigations by Victoria Police and Racing Victoria we are not at liberty at this time to disclose the identities of the persons arrested nor the details of the investigations.
"Racing Victoria is committed to maintaining the highest integrity standards in our sport and, where appropriate, we will continue to work with Victoria Police on those investigations."
Weir is one of Australia's best-known horse trainers and was behind the 2015 Melbourne Cup winner Prince of Penzance.
He's Australia's most prolific and successful trainer.
Victorian Racing Minister Martin Pakula said the investigation showed authorities were enforcing rules "without fear or favour".
"As minister for racing and a racing lover, I'm committed to maintaining the integrity of our sport and any allegations of breaches are extremely disappointing," he said in a statement.