Trainers and employees linked to racing industry heavyweight Aquanita have been accused of administering Vicks Vapor Rub and sodium bicarbonate to horses just before a race.

Eight people, including five trainers, were charged on Tuesday following a three-month investigation by Racing Victoria.

The investigation began on 7 October, when Greg Nellingan, a stablehand for Aquanita trainer Robert Smerdon, allegedly administered sodium bicarbonate through a nasal tube to a bay mare called Lovani, who was then withdrawn by steward’s order from the 1400m Paris Lane Handicap at Flemington.

Smerdon stood down as director of Aquanita one month into the investigation.

Sodium bicarbonate, or bicarb soda, can be used to counteract lactic acid buildup in racehorses and cause a delay in the onset of fatigue, giving what the president of the Australian Veterinary Association of Victoria, Dr Paul Martin, called “a 1% edge”.

“What makes an athlete tire is the build-up of lactic acid in the body, which then says to the nervous system, ‘slow down’,” Martin told Guardian Australia. “It’s pretty well proven that giving extra levels of bicarbonate can delay the onset of fatigue … it could be the difference between first or fourth.”

Martin said the practice did not hurt the horse and led to a quicker recovery time, but added that vets did not approve because it could take away from efforts to ensure a horse was fit enough to run.

The use of sodium bicarbonate or other alkalising agents, above a certain level which a horse can consume in its food, is forbidden under the Australian rules of racing.

Smerdon was charged with being party to the administration of alkalising agents or other medications to a horse on race day on 115 occasions between 2010 and 2017.

He was also charged with instructing Nellingham to put Vicks Vapor Rub on the nose of a gelding named Disco Dan before running him in a race at Bendigo in October 2010.

Vicks, said Martin, is believed to open up a horse’s airways and allow them to take in more oxygen during a race, though there is no scientific evidence to suggest it works.

The use of Vicks and a range of other treatments or medication, including anything administered by stomach tube (such as sodium bicarbonate), paste, syringe, topical application or inhalation, is prohibited in the 24 hours prior to a race.

Acupuncture, chiropractors, and other nerve manipulation treatments are also banned on race day.

Nellingham was charged with administering an alkalising agent or other medication on race day on 123 occasions, including to Lovani; possessing a modified syringe on the day that Lovani was disqualified; putting Vicks on Disco Dan; placing a total of $530 in bets against three horses he had care of; and failing to comply with the Racing Victoria investigation.

Also charged were Denise Nelligan, accused of being party to the use of sodium bicarbonate or other medication on 13 occasions between 2011 and 2017; fellow Aquainta trainer Stuart Webb, accused of the same on three occasions; stablehand Daniel Garland, two occasions; trainer Liam Birchley, three occasions; Caulfield Cup winning trainer Tony Vasil, seven occasions between 2010 and 2013; and trainer Trent Pennuto, four occasions.

The chief executive of Racing Victoria, Giles Thompson, said the allegations were “very serious”.

“Racing Victoria’s primary objective is to protect the integrity of the sport and to enforce the Australian rules of racing, ensuring both a level playing field for all and the health and welfare of all horses competing in Victoria thoroughbred races,” Thompson said in a statement.

“It is vital that in order to maintain a world-class thoroughbred racing industry that we have a world-class integrity regime that is strictly enforced.”

The eight people charged will appear before the Racing Appeals and Disciplinary Board at a later date and stewards are considering whether they will be stood down in the mean time.