The five Victorian trainers charged with cobalt offences have been asked to show cause why they should not be suspended pending their hearings.

Peter Moody, Mark Kavanagh, Danny O'Brien and the partnership of Lee and Shannon Hope, all of whom have had horses test above the cobalt threshold of 200 micrograms per litre of urine, were issued show-cause notices on Friday.

The five, who are collectively facing 32 charges, have been asked to appear before Racing Victoria stewards on July 29 to explain why they should be permitted to continue training.

The charges against Lee and Shannon Hope are scheduled to be heard on October 15, 16 and 19. Dates have not been set for the hearing of the charges against Kavanagh, O'Brien and Moody.

Veterinarian Dr Tom Brennan of the Flemington Equine Clinic is at the centre of cases in Victoria and NSW and has been charged in both jurisdictions.

Brennan's involvement came to light in the NSW case against Sydney trainer Sam Kavanagh who named Brennan as the supplier of a substance labelled Vitamin Complex which was analysed and found to contain cobalt.

After telling the Sam Kavanagh inquiry he was not the source, Brennan this week changed his evidence and said he had not only supplied Vitamin Complex to Sam Kavanagh but also Mark Kavanagh and O'Brien but said he did not know it contained cobalt.

Sam Kavanagh was stood down on May 21.

He faces a raft of charges relating to cobalt and other substances which surfaced after Midsummer Sun tested positive to caffeine and cobalt following his Gosford Cup win in January.

Newcastle trainer Darren Smith was stood down in May last year and this week lost a second appeal against a 15-year disqualification.

Brennan has agreed to stand down from August 1 pending his hearings in both states.

Racing NSW stewards will begin four days of hearings from August 3 beginning with the charges against Sam Kavanagh, Brennan, and Flemington Equine practice manager Aaron Corby.