The man who treated Midsummer Sun on the day he won the Gosford Cup says he gave the horse a drench containing beetroot and aspirin but not cobalt or caffeine.

Mitchell Butterfield was commissioned by harness racing identity John Camilleri to drench horses at Rosehill on January 7, at a stable he found out belonged to Sam Kavanagh when he arrived the track.

With the assistance of Camilleri, he drenched two horses with a substance handed over by a man Butterfield later identified as Kavanagh employee Michael O'Loughlan.

Camilleri asked him to come back two days later with his own drench.

Butterfield told Racing NSW stewards on Thursday that after he treated the horse with his own mixture, O'Loughlan handed him a syringe and asked him to inject the horse, which he did.

"My drench has beetroot extract, echinacea powder, sugar, Berocca and aspirin," Butterfield said.

"There was no cobalt in the drench.

"The old fella asked me if I could give the horse an injection so I did.

"Afterwards I asked him what it was and he said formaldehyde and vitamin C.

"It looked like apple juice but it could have been anything.

"He could have taken a piss in it and given it to me."

Butterfield said he put two and two together and figured out the horse was Midsummer Sun because it was the only Kavanagh horse racing that day.

He put $500 on the horse which won and later produced a positive swab to caffeine and high levels of cobalt sparking an inquiry which has led to charges against Butterfield, Camilleri, Kavanagh and O'Loughlan along with Flemington Equine Centre vet Dr Tom Brennan and practice manager Aaron Corby.

All except Butterfield and Corby have been charged with giving false evidence to stewards.

On Wednesday Camilleri said a text he had sent to a journalist saying he knew of a Melbourne Cup winner who raced on cobalt, was "big-noting".

It did however prompt Racing Victoria's chief steward Terry Bailey to respond on Thursday that testing of Melbourne Cup winners for EPO began in 2009 with no adverse findings.

"We are of the view that the text message sent by John Camilleri lacks substance, which Mr Camilleri himself admitted during the course of yesterday's hearing," Bailey said.

"The past six Melbourne Cup winners, commencing with Shocking in 2009, have been all subjected to EPO testing in the lead-up to and/or immediately after their Cup victories and none have returned a positive swab.

"Racing Victoria was the first thoroughbred racing jurisdiction to introduce a threshold rule for cobalt in April 2014 and the only Melbourne Cup winner since the rule was introduced, Protectionist, returned a clear sample."

Sam Kavanagh, who faces a raft of charges, has named Brennan as the source of a substance called Vitamin Complex found in his stable and later discovered to contain 175 times the amount normally found in a supplement.

He gave evidence earlier this week he had never met Camilleri before the January drenchings but had been put in touch with him by former Flemington Equine Clinic vet Adam Matthews.

The inquiry will hear final submissions from all parties next Thursday.