California racing officials have identified a connection in the sudden death of six horses with trace amounts of anticoagulant rodenticide in their systems, the state horse racing board was told Dec. 18.

Rick Arthur, DVM, California Horse Racing Board (CHRB) equine medical director, said the horses, who died between Dec. 21, 2012, and Sept. 18 of this year, all expired due to internal bleeding following exercise. Necropsy exams found each had only trace amounts of a strongly toxic anticoagulant used in the extermination of rodents at racetracks in their systems.

Arthur said the level of toxicity found in these cases was so low it would not have been enough to kill the horses, but in combination with exercise he believes the poison proved fatal.

The same rodenticide was found in one of the seven horses trained by Bob Baffert that died suddenly following strenuous exercise at the now-closed Hollywood Park between late 2011 and 2013