The father-and-daughter training combination of Terry and Karina O'Sullivan are facing a second prohibited substance case.

Racing Victoria stewards are continuing investigations into a high cobalt reading taken from Darragh in a pre-race urine sample at Ballarat in November.

The O'Sullivans, based at Stawell in rural Victoria, have also been charged after dexamethasone, a short-acting corticosteroid, was detected in a post-race urine sample from Dandy Gent on September 2.

Dandy Gent finished second behind Sir Laszlo in a 2400m race.

The charges will be heard by the Racing Appeals and Disciplinary Board at a date to be fixed.