Only two kinds of forestland exist in Louisiana ... one that has feral hogs and the other that will soon have feral hogs.
The search for a way to control the state’s feral swine population has been an ongoing effort for a long time, but Dr. Glen T. Gentry, with the help of the LSU chemistry department, is making another tool that could help.
A bait using sodium nitrite gives the wild pigs a dose high enough to be lethal, but breaks down fast enough that it won’t affect the environment or scavengers that might feed off the carcasses of the swine.
Hogs first arrived in North America in the 1500s brought by Spanish explorers. The practice of keeping pigs was free-range, so escapes from domestic enclosures allowed the animals into the wild, according to information from the LSU AgCenter. Then in the early 20th century, more aggressive Eurasian wild boars were brought to the United States to be hunted. Many of those escaped into the wild and bloodlines were mixed with the previously escaped domestic hogs.
No hunting season exists for feral hogs. In 2017, the Louisiana Department of Agriculture & Forestry introduced a way to capture feral hogs live so that processors could use the meat commercially.
Agriculture & Forestry Commissioner Mike Strain has said more than 350,000 feral hogs are killed each year, “and the population is still exploding.” The commissioner estimates that each year roughly $50 million of damage is caused by the most prolific large mammal in North America.
Enter Gentry, a full professor at LSU and resident director of the Bob R. Jones - Idlewild Research Station for the LSU AgCenter, but he might be better known in some circles as the feral hog specialist.
“Probably six or seven years ago, they tapped me to come up with a toxic bait for feral swine and we’ve been working at it ever since,” Gentry said. “It’s some of the extension part of what I do.”
Since then, Gentry has spent a lot of time educating people around the state about the feral swine and explaining what he was working on, hence the feral hog specialist title bequeathed to him (though you won’t find that on his business card).
The use of sodium nitrite came at the request of the U.S. Department of Agriculture (USDA) and Environmental Protection Agency (EPA), but that was the only instruction. Unlike a poison, which can accumulate in the environment or harm other animals that eat the swine carcasses, sodium nitrite breaks down and won’t harm others.
“Sodium nitrite is relatively safe for humans,” Gentry said. “When a mammal consumes sodium nitrite, it induces methemoglobinemia. So, your hemoglobin changes form and it cannot carry oxygen.”
Humans also have an enzyme that reduces its reaction to sodium nitrite in their bodies.
“Pigs have that enzyme, but they don’t have as much of that enzyme and they can’t produce it very fast,” Gentry said.
In tests, the feral hog specialist said researchers discovered it took 189 mg (or 189 parts per million) of sodium nitrite to make a lethal dose for feral pigs.
“The USDA says that humans can (safely)consume finished products having 200 parts per million of sodium nitrite,” Gentry said. “Pigs are just more sensitive to sodium nitrite than humans are, by a long shot.”
Sodium nitrite is used as a food preservative, said Dr. John Pojman, professor and chair of the Department of Chemistry at LSU, and is safe for humans.
“People buy it, I think it’s called Prague salt, which is used for preserving meat,” he said.
Before figuring out how the sodium nitrite would be delivered to the feral swine, Gentry said they worked on taste. The baits had to taste better than one of the animals’ favorite foods: corn.
“We went through all kinds of iterations trying to determine what pigs like to eat,” Gentry said. “We found they would consume dehydrated fish before they would consume whole-shelled corn. So, that’s what we used to make our bait matrix, thinking that pigs would come to a feeder with whole-shelled corn, because there’s tons of those types of feeders out there. You could release these baits ... they would leave the whole-shelled corn, eat the baits and then go back to eating the whole-shelled corn.”
Dehydrated bass was used in the first testing, then porgy were used. Gentry said the next test will use fish meal to see if it will get the same response.
After finding a taste the swines would desire, the next challenge was to keep sodium nitrite in the presented form so that it doesn’t break down in the environment. Although not causing problems, if the compound breaks down, the hog might not get a lethal dose. Also, when the feral pig consumes the bait, it shouldn’t crumble, lessening the amount the animal actually consumes and allowing other animals the possibility of eating it.
Pojman said when Gentry came to him with the proposal, they first thought of trying to encapsulate the dose. However, Gentry later settled on something else.
“I wanted to have something with the consistency of gummy bears,” Gentry said, a texture that would make it easy for the animal to eat smaller pieces that might break off.
However, there also was the issue of the bait breaking down and losing its potency. Gentry said if exposed to air, sodium nitrite breaks down into sodium nitrate, which is less toxic to animals.
“Glen had already made a bait the hogs would eat,” Pojman said. “We just had to find a way to keep the nitrite in it stable so it wouldn’t break down until the hogs ate it.”
The problem occurs if the sodium nitrite gets acidic, Pojman said. To keep it from becoming acidic and breaking down, which gives off an odor similar to chlorine, Pojman and his graduate students used an antacid. That stabilized the compound.
“It’s not cruel; it’s a very humane way to kill a hog,” Pojman said. “They just fall asleep and it kills them. And if they don’t eat enough, the wake up and be fine. It really is amazingly humane.”
The baits are about the size of a golf ball and includes about 8 grams of sodium nitrite.
“One of those baits can kill about a 98-pound pig,” Gentry said. “It takes about an hour and 45 minutes to two hours.”
So what if the pig gets a nonlethal dose of sodium nitrite and is later killed by a hunter?
“Unless he eats the stomach contents themselves, there’s some work coming out of Texas that says it’s safe,” Gentry said.
With taste and dosage starting to work out, next is a delivery system that gives the least chance of the baits being left out in the environment for birds or other animals to eat. Gentry said that’s why he is developing a remote feeder for the baits.
“The idea was you get one of these wildlife feeders all these hunters use ... and you hang this machine on the side of the wildlife feeder, and you set a camera up” Gentry said.
When the camera sends to a smartphone photos of the feral pigs feeding, the user can send a message through the device and have a determined number of the baits released.
“So you only release the number of baits you need at any given time,” he said.
The feeder is still being developed, but so far it can hold about 50 baits.
“The goal is not to just dump it out into the environment. You’re releasing it selectively,” Pojman said.
As prolific as the feral swine are, Gentry said developing a bait that kills them will not eradicate the animals.
“There’s no way that can happen,” he said, but it can be another tool to control population, which includes hunting and aerial gunning, for example. “You’ve got to kill 75 percent of the population that’s there now just to hold numbers static.”
Pojman said because the bait uses such simple chemistry, it can be easily mass produced and is inexpensive to do so. However, the final formula is still being worked on as the project is still in the optimizing stage.
“So we’d like to optimize it so we have the least number of baits so that the hogs still want to eat and have the highest amount of (sodium nitrite) so it can be more effective,” Pojman said.