Eight people have been found guilty of taking part in a doping “conspiracy” that the Racing Appeals and Disciplinary Board has dubbed “probably the biggest scandal and the most widespread investigation in the history of Australian racing”.

The five trainers and three stable hands, including the former director of Aquanita, Robert Smerdon, were found guilty of involvement in a doping ring that used sodium bicarbonate or other alkalising agents to “top up” horses before a race.

Alkalising agents are used to counter the buildup of lactic acids and delay the onset of lactic acids, giving horses “a 1% edge.”

In a decision handed down on Tuesday, the disciplinary board said it was “comfortably satisfied” that all eight accused were involved in what it described as a “long-running systematic conspiracy to try and obtain an unfair advantage in well over a 100 races over seven years”.

“The Aquanita case represents one of the darkest and longest chapters in the history of the Australian turf,” the board said. “There is a litany of brazen attempts to cheat and to obtain an unfair advantage over many years by a well-organised team.”

Trainers Smerdon, Liam Birchley, Tony Vasil, Stuart Webb and Trent Pennuto, drivers Gregory Nelligan and Daniel Garland, and stable hand Denise Nelligan were charged in January.

Together, they faced 271 charges, most of which were under section 175 (a) of the Australian rules of racing against “dishonest, corrupt, fraudulent, improper or dishonourable action”.

All pleaded not guilty, either explicitly or by failing to formally register a plea, and only Birchley actually attended the hearing and gave evidence.

The charges arose out of an incident on 7 October 2017, when Gregory Nelligan, a float driver for Aquanita, was caught inserting a syringe containing the “top up” mixture into the mouth of racehorse Lovani at Flemington racecourse.

Investigators seized his phone and identified 1,000 messages they said related to the use of “top-ups” and identified the other seven people charged.

Smerdon and Nelligan were also found guilty of other charges, including applying Vicks VapoRub to a horse named Disco Dan at Bendigo racetrack in 2010. Vicks is believed to allow a horse to take in more oxygen during the race but there is no scientific evidence that it works.

In an 11-page judgment, the disciplinary board said Nelligan was “the architect and, to some extent, the promoter of the ‘top-ups’ scheme” and was involved in the use of “top-ups” on 123 occasions, at the request of Smerdon or other trainers.

Smerdon, the board said, was involved in 115 occasions when “top-ups” were administered and was the “driving force” along with Nelligan, who was “considerably lower down the chain of command”.

Smerdon stood down as a director of Aquanita as a result of the scandal, and the company has since rebadged as Neerim Lodge.

The board said that the claim by Smerdon and others that the phrase “top-up” used in the text messages referred to feed and water was “palpable nonsense”.

Addressing the charges against Birchley, the board said: “Incidentally, any suggestion that ‘top-ups’ are feed and water is well and truly laid to rest by the suggestion that Gregory Nelligan could carry them in his pockets.”

Birchley was described by the board as a non-paying customer of “top-ups” on three occasions between 2011 and 2015. He has already said he would appeal the decision.

The chief executive of Racing Victoria, Giles Thompson, said the guilty verdicts send “a very strong signal to anyone who thinks they can undermine the integrity of the sport by actively breaching the rules of racing”.

“It also is a ringing endorsement of the investigative work of our integrity services team who found these breaches and ran an exhaustive four-month investigation before laying charges against these eight people,” Thompson said in a statement.