The New Jersey Racing Commission has tightened its rules to allow horses to be tested at farms and on days when they are not competing. The old rules said horses could only be tested at tracks on race days.
The six horses who tested positive for illegal performance-enhancing substances have a California owner and a trainer from Clarksburg.
Racing officials acting on a tip tested the horses at Winner's International Farm in Chesterfield last month.
Officials are looking at whether the trainer and owner violated commission rules.
