by T.D. Thornton
The rat poison found in the livers of six horses that died from internal hemorrhaging almost certainly entered the horses' systems after stable employees moved commercial pest control bait closer to and even into stalls in an attempt to more effectively control rodents, a California Horse Racing Board safety official testified at the commission's Dec. 18 meeting.
“I saw no indications of imported feed or other material contamination, and no evidence that the rodenticides are being used for performance enhancement as suggested by some as a blood thinner,” Jeff Salmon, head of the CHRB's track safety program, told the commissioners. His backstretch inspections, conducted over the past year, were part of the board's ongoing investigation into a spate of sudden equine deaths dating as far back as 2011.
Dr. Rick Arthur, the CHRB equine medical director, told TDN on Friday that while the determination of anti-coagulant poisoning explains the mystery of the unusual deaths, his team will continue to “refine our diagnostic capabilities” and will actively investigate any other sudden equine deaths that occur at California racetracks.
“The bottom line is we don't think there's any malfeasance,” Arthur said of the poisonings. “We think it is accidental and unintentional. It is a difficult issue, and part of the problem is we have to look at alternative ways for rat control. There's not a racetrack in this country that does not have a rat problem.”
At the Dec. 18 meeting, Arthur cited a study he co-authored in the January 2015 issue of the Journal of Veterinary Diagnostic Investigation that examined the sudden collapse and death during exercise of five horses (a sixth death occurred after the article was submitted for publication). In all of them, massive hemorrhaging was observed in necropsies, and low-toxicity levels of the pesticides brodifacoum, diphacinone, or bromadiolone were detected.
Although only traces of the poisons were found, it is speculated that exercise-related increases in blood pressure may have reduced the threshold for toxicity, causing the deaths.
The report further cited evidence that the use of phenylbutazone (Bute) may have potentiated the poisons in at least two cases.
Arthur said rodenticides had not been part of the standard toxicology screen until the CHRB began investigating the deaths of seven horses trained by Bob Baffert between 2011 and 2013, and that at first his team was “grasping at straws” in looking for rodenticide poisoning.
But when one of the Baffert trainees showed traces of the poison, the testing was expanded to all horses whose deaths could not be otherwise explained.
For comparison, Arthur said necropsies on 27 California racehorses that died during the same time period from musculoskeletal injuries were also tested for the presence of rodenticides, but none were found.
“All of the horses [with traces of poison] died during or after exercise, which is very important,” Salmon said. “There's no other explanation for why the horse would bleed so much internally.”
Salmon explained that brodifacoum is considered a “second-generation” rodenticide. Such poisons are far more potent than “first-generation” rodenticides that have been phased out over the past three decades because rats have developed a resistance to them.
“They stay in the horses' system a long time,” Salmon said, from between four and 12 months.
Salmon said Santa Anita, Del Mar and Golden Gate Fields are three California tracks that hire commercial pest control vendors (as of July 1, the use of second-generation pesticides by individuals has been banned in California). The companies place the rodenticides on the perimeter of shed rows, but stable employees move them closer to horses, thinking they are helping to control rats.
“Rodenticide bait theft is common,” Salmon said. “What happens is that backside personnel will loot the stations or remove them completely, and they use them in a way that they see fit. Oftentimes, the rodents will actually burrow up into a particular stall. I saw instances of poison being placed inside the burrows in an area where we wouldn't want to see it put in. The most probable source of the anti-coagulant rodenticide that is showing up in these horses in my estimation is unauthorized use. I saw many instances of ample opportunity for contamination in feed bins and other sources.”
CHRB first vice chair Bo Derek said called for “aggressive” action because “it doesn't seem that our horses and these anti-coagulants are compatible in a living situation.”
Salmon said that an outright ban on second- generation rodenticides is not feasible because there is no other plan in place to effectively control the rat problem. He said the first step will be an education outreach program to get backside personnel to understand the grave dangers of the poisons.
Salmon also suggested that at tracks where stabling is ample, horses could be rotated into different barns while vacant stalls are more thoroughly eradicated of vermin.
Arthur said he knows of no proactive blood test that would detect the presence of the poisons in a horse's liver. “We just don't think we can identify this ante-mortem,” he said.
Board members discussed the use of cats as natural predators for rats. But Arthur said putting out food for cats only lures possums, which creates an EPM (equine protozoal myeloencephalitis) hazard.
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