In 2022, the Iowa State University Veterinary Diagnostic Laboratory received eight reports of anticoagulant rodenticide exposure in pigs.

That number stood out to the toxicologists at the VDL. According to the Food Animal Residue Avoidance Databank, in a recent publication, from 1999 to 2021 only 23 cases were reported in general.

“The majority of those cases of course were all market weight animals from two days to two weeks before slaughter,” said Chris Rademacher, a clinical professor in veterinary medicine at Iowa State University. “And some of the commonalities, between those cases, were they'd have a pen or two of pigs that broke out of the pen, they'd gain access to the office or the storage area. When they would come in, they found notable amounts of rodenticide that was gone, so anywhere from five to 25 pounds of rodenticide that was missing.” 

Afterwards in most cases the animals were just returned to the pens, which held anywhere from 35 to 400 pigs.

In seven of the eight cases, the exposed animals were returned to pens unidentified, with no marks, paint or ear tags. In one case, they were able to tell which pigs were exposed and identified and penned those separately.

Rademacher said the situation drew more questions than answers. What animals were exposed? Could they be identified and can they be marketed?

That's when the VDL got involved, however Rademacher noted testing was limited.  

“It can be done ante-mortem. There's a whole blood test, that covers the majority of anticoagulant rodenticides. If you catch it within a week or so of exposure, you could look at it,” Rademacher said. “You could do some postmortem analysis of the livers since most of these are concentrated in the liver. But I can tell you the packing plant doesn't have a whole lot of interest in harvesting them there and then holding the carcasses that maybe they'll be negative.”

Withdrawal times are dependent on dose, length of exposure, compound, toxicokinetics, animal age and time to market. The FARAD has protracted withdraw times to be expected but they are not clear cut, Rademacher said.  

For first-generation anticoagulant rodenticides, one study estimated a conservative withdrawal period of 160 days. In second-generation ones, residues have been estimated, through the extrapolation of data, to be detectable in the liver up to 176 weeks and in the muscle up to 62 weeks following high dose exposure.

Since the exposed animals in seven cases were unable to be identified, the pigs were rejected by the packer and whole pens had to be euthanized. For disposal, rendering was not an option. Burial and composting could be options; otherwise, it came down to incineration. Each has potential legal ramifications, Rademacher says.

“You need to really be thinking about proper storage of pesticides. On the floor, in the office or on the shelves that’s not acceptable,” Rademacher says. “They should be in a lock box or kept off site. And then as always, if you're doing bait replacement, you want to put them into bait boxes. Proper bait placement is key, not up on the shelves.”

These preventative measures can aid in avoiding these situations entirely. For pigs that do get exposed to anticoagulant rodenticide, Rademacher says it is important for producers to calmly assess the situation and mark animals that have a known exposure. Avoid tanking entire pens due to lack of identification.

During the 2023 Iowa Swine Day, Rademacher summarized many of the key items that were presented at the 2023 McKean Swine Disease Conference, including recent reports by ISU VDL Toxicologist Scott Radke.