New Toxin for Feral Swine

By Joshua Rapp Learn

The Wildlife Society

Posted on October 23, 2015

Feral swine are one of the most difficult invasive species to eradicate in North America. The pigs (Sus scrofa), first introduced from Europe, are intelligent enough to avoid many traps and can change their behavior to be more evasive and nomadic once they’ve had encounters with hunters.

But researchers from the U.S. Department of Agriculture’s Wildlife Services are perfecting a poison that’s as basic as bacon for breakfast: salt.

“How it kills the animals is by reducing the ability of the red blood cell to release oxygen to the tissues,” said Kurt VerCauteren, the feral swine project leader for Wildlife Services at the National Wildlife Research Center in Fort Collins, Colo. at a presentation at The Wildlife Society’s ongoing annual conference in Winnipeg.

There are a number of toxicants that can be used to kill feral swine, but as of yet none have been registered in the U.S., he said. Techniques currently focus on trapping, relocating, hazing, contraception, killing and snaring. But, VerCauteren has been working with other researchers to develop a toxicant based on sodium nitrate — a kind of salt that, ironically, is sometimes used to preserve pork.

While safe in small quantities, high enough quantities of sodium nitrate can kill anything.


VerCauteren said that using salt in its basic form is relatively cheap, but the researchers have to implement a more expensive process to keep the pigs from smelling trouble. They microencapsulate the salt so that it’s odorless to the swine, yet will still break down in their digestive systems and kill them.

The toxicant has been very effective so far. While initial tests showed an 85 percent mortality, the researchers have improved their technique to kill up to 95-100 percent of the pigs that consume the toxicant.

VerCauteren said they’ve delivered the toxicant to pigs in tests using peanut butter, though they make it look black and dirty in an attempt to “make it as unattractive to other animals as possible.”

And herein lies one of the other challenges. The researchers are working on improving the delivery design to create devices that only feral swine can access.

This proved particularly difficult with crafty racoons (Procyon lotor) — the bigger ones can push open the lids on bait boxes that weigh up to 28 pounds. “There are photos of racoons pushing [the box] like a weight lifter, with another one on top,” VerCauteren said. As a solution, the researchers made the lid weigh more than 30 pounds — a weight that even the biggest raccoon shouldn’t be able to cope with.

While the toxicant shows some promise, VerCauteren said that it will still take around 18 months for the Environmental Protection Agency to review the product. But, if everything goes well, they could be giving feral pigs an overdose of salt in as little as two years.

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