Three prominent Australian horse trainers, including Peter Moody who trained champion mare Black Caviar, are under investigation after horses in their stables tested positive for cobalt chloride, a banned blood doping substance. Peter Moody and fellow trainers Mark Kavanagh and Danny O'Brien will face racing stewards regarding the positive tests. Racing officials said they are investigating how cobalt entered the horses' systems and will gather all facts before making determinations in each case.