Five horse trainers and three stablehands have been found guilty of doping-related offences by Victoria's Racing Appeals and Disciplinary Board, after an investigation into one of the biggest horseracing scandals in Australian history.

Trainers Stuart Webb, Tony Vasil, Trent Pennuto and Liam Birchley, and stablehand Daniel Garland had all pleaded not guilty.

Trainer Robert Smerdon reserved his plea, and stablehands Greg and Denise Nelligan entered "no contest" pleas.

Together, they faced 271 charges.

Who did what at Aquanita: Leading trainer Robert Smerdon was a "driving force" behind the scheme; administered "top-ups" and provided instructions

Leading trainer was a "driving force" behind the scheme; administered "top-ups" and provided instructions The Racing Appeals and Disciplinary Board (RAD) called Gregory Nelligan the "architect" and chief administer, who injected "almost always" on race days

The Racing Appeals and Disciplinary Board (RAD) called the "architect" and chief administer, who injected "almost always" on race days Nelligan's wife Denise Nelligan confessed but later tried to backtrack, RAD said. She relayed instructions and administered "top-ups"

Nelligan's wife confessed but later tried to backtrack, RAD said. She relayed instructions and administered "top-ups" Trainer Tony Vasil was found guilty of requesting "top-ups" for his horses on race days via text message

Trainer was found guilty of requesting "top-ups" for his horses on race days via text message Trainer Stuart Webb was also implicated in text messages, advising and asking for "top-ups" to be given

Trainer was also implicated in text messages, advising and asking for "top-ups" to be given A driver at the stable, Daniel Garland , was found guilty of being complicit in the cover up and administering to horses

A driver at the stable, , was found guilty of being complicit in the cover up and administering to horses Licensed trainer Trent Pennuto was acting as a foreman at the time and requested "top-ups" for horses under his care

Licensed trainer was acting as a foreman at the time and requested "top-ups" for horses under his care Registered as a visiting trainer, Liam Birchley worked for Aquanita and also independently. He requested "top-ups" for his horses

In its findings, the board described the case as "probably the biggest scandal and the most widespread investigation in the history of Australian racing".

"This was a long-running systematic conspiracy to try and obtain an unfair advantage in well over a hundred races over seven years," it said.

"There has been dishonest, corrupt or fraudulent, improper or dishonourable actions of the highest order."

Racing Victoria, through lawyer Jeff Gleeson QC, had previously told the board that the eight racing professionals were involved in "knowing, brazen and systematic" doping between 2010 and 2017.

The charges included administering horses with banned race-day treatments, including sodium bicarbonate, or "top-ups", over the seven-year period.

It can enhance performance by slowing the build-up of lactic acid, so horses can run longer without tiring.

Stablehand caught in box with syringe

Last month, the board saw footage of racing stewards confronting Nelligan as he was allegedly doping a Smerdon-trained horse at Flemington.

The video footage — which the board declined to publicly release — showed Nelligan in a box with the racehorse Lovani and a modified syringe plunger allegedly containing sodium bicarbonate paste concealed in a yellow plastic bag last October.

When officials asked him what he was doing, Nelligan could be heard saying "no-one else has got anything to do with it" and claiming the pink paste on Lovani's mouth and bit is "something I made up … it's a gel".

Mr Gleeson told the hearing Nelligan made a "forlorn attempt" to hide the plunger under his clothes.

Nelligan's phone was then seized by authorities, who used 1,000 text messages as evidence that pointed to the varying level of culpability of those involved.

Racing Victoria sends warning

Penalty submissions for the eight people found guilty — who all had links to the Aquanita Racing stable — will be heard on Thursday.

Racing Victoria's chief executive, Giles Thompson, said the guilty verdicts sent a "very strong signal" to the racing industry.

"All sport, no matter where it is in the world and the type of sport it is, has to be realistic — there are going to be people out there who do try and cheat," he said.

"What we have to do is make sure that we are putting those resources in, and I think racing in Victoria is at the forefront of this globally.

"I think the participants and those who what to engage in the sport should feel confident that we are doing what we need to do."

Racing Minister Martin Pakula said it was "a good day for racing" and praised the work of the integrity unit.

"It shows that if you want to do the wrong thing, if you are determined to breach the rules of racing, you will be caught, you will be prosecuted, you will be found guilty," he said.

He said the outcome was proof the integrity department is well-resourced and operates "without fear or favour".