Racing Victoria has introduced a threshold level for the substance cobalt to prevent its potential use as a performance enhancer in thoroughbred racing.

A new local rule will start on April 14, stating cobalt is a prohibited substance at a concentration of greater than 200 micrograms per litre in urine.

This threshold applies to race days and out of competition.

Racing Victoria's head of integrity, Dayle Brown, said cobalt was found naturally in horses but at levels far less than the threshold set.

He warned trainers that penalties would follow if any horse was found to be above the published threshold level.

Brown says cobalt is an endogenous substance and an increase in levels can aid a horse's performance.

"In simple terms it means that the administration of cobalt can assist in generating more red blood cells to carry oxygen through the body and thus allow a horse to perform at a peak level for longer without the onset of fatigue and lactic acid," Brown said.