Training partners Lance O'Sullivan and Andrew Scott have been charged over cobalt irregularities in three of their horses, including a placegetter in last year's NZ Derby.

The pair, who operate Wexford Stables at Matamata, have been charged with three breaches of the rules following an investigation by the NZ Racing Integrity Unit.

Three horses were found to have cobalt in their systems above the allowable threshold after races early last year.

Wexford Stables claimed their horses had been exposed to heavily cobalt-dosed water troughs the horses shared with dairy cattle but the RIU says the readings came about by the oral feeding of cobalt in high concentrations.

It has applied to have Sound Proposition disqualified from its third placing at the NZ Derby last year, and have the first placings of Quintastics at Matamata on March 11 and Suffire at Tauranga on February 5 also scrubbed out.

According to the RIU, Quintastics was more than three times over the limit, while Sound Proposition was more than twice the allowable threshold of 200mcg per litre of urine.

The charges will be heard by the Judicial Control Authority.

The trainers could face up five years suspension or disqualification and up to a $25,000 fine.

A former champion NZ jockey, O'Sullivan was last week inducted into the NZ Sport Hall Of Fame.