Former Flemington Equine Clinic vet Dr Adam Matthews gave evidence on Wednesday to a fiery appeal, on the eve of the Spring Racing Carnival, of bans imposed on two of the country's best-known trainers, Mark Kavanagh and Danny O'Brien, for cobalt doping.

Mr O'Brien and Mr Kavanagh were issued with bans after horses in their care tested positive for cobalt during the 2014 spring racing carnival.

They are appealing those bans in the Victorian Civil and Administrative Tribunal.

Dr Matthews gave evidence on Wednesday after being released from an institution, where he is being treated for an undisclosed psychiatric illness.

Appearing to choke back tears, he agreed he had battled a "severe" gambling problem all his life, and said he had turned over $4 million in about three years.

Dr Matthews also agreed that Sydney trainer Sam Kavanagh, who was disqualified earlier this year for doping but who is appealing his disqualification, had deposited money into his wife's TAB account in return for veterinary products.

Dr Matthews' former boss, Dr Tom Brennan, has previously named him as being behind the supply of horse supplements that led to positive tests for cobalt in horses trained by Mark Kavanagh and Mr O'Brien.

This is denied by Dr Matthews.

He told the hearing he had prepared vitamin complexes for his clients, containing a range of ingredients including Vitamin B, B12 and Aminoplex. But he denied ever supplying cobalt, saying "I was very anti-cobalt".

Dr Matthews claimed that his former boss had used him as a "scapegoat" for the supply of the banned substance.

And he appeared to point the finger back at his former boss, telling the hearing that he had seen one of Dr Brennan's "girls" making up a drip to administer to a horse that seemed "unusual".

"I saw some stuff that was unusual going in there," Dr Matthews said, including VAM - a substance that contains cobalt.

"He was a bit secretive about it."

Dr Matthews claimed Dr Brennan "waged a war" against him after their professional relationship broke down, which led to him losing personal relationships and contemplating suicide.

In July, Dr Brennan withdrew an appeal against a five-year disqualification for cobalt, the day before it was due to be heard at VCAT.

Asked by counsel for Racing Victoria, Jeffery Gleeson QC, whether it was purely coincidence that trainers he had been working with had horses testing positive to cobalt, Dr Matthews replied: "there were positives all over Australia at that time".

One trainer whose horse tested positive was Peter Moody, who was cleared in March of deliberately administering illegal levels of Cobalt to his stallion, Lidari, who recorded elevated cobalt reading after the Turnbull Stakes in October 2014.

Mr Moody was found guilty of a lesser charge relating to the non-intentional administration of cobalt to a racehorse.

Under sustained questioning from Mr Gleeson, Dr Matthews agreed that minutes after news that Mr Moody had been accused doping his horse broke, Sam Kavanagh texted Dr Matthews to say: "Are you sure we're okay?"

Dr Matthews replied: "???"

​The hearing continues.