Belinda Dunn is the latest trainer to be charged by Racing Victoria stewards in relation to cobalt.
The Dunn-trained Margot's Boy tested above the allowed level of cobalt in a urine sample after winning a benchmark-58 race on his home track at Tatura on September 23 last year.
Two laboratories confirmed cobalt at a concentration in excess of 200 micrograms per litre in urine.
Under the Australian rules of racing, cobalt is a prohibited substance above 100 micrograms per litre in urine.
Stewards have charged Dunn with administering, or causing to be administered, a prohibited substance for the purpose of affecting the performance or behaviour of a horse in a race.
Dunn has also been issued with alternative charges of administration of a prohibited substance that was detected on race day, and another of presenting a horse to race when a prohibited substance was detected in its system.
A date for the Racing Appeals and Disciplinary Board hearing into the charges has yet to be set.