Feral pigs that arrived with settlers in the New World in the early 1500s have overstayed their welcome, according to farmers and public land managers plagued by their destructive behavior. The animals gained popularity with big-game hunters in decades past, leading some states to stock the animals in the wild for sport. But feral swine, which breed abundantly, now number in the millions in the U.S. They cause more than $1 billion in damage nationwide to agricultural fields and native habitats each year with their aggressive rooting and roaming.
“Feral swine are a very intelligent, very strong animal,” says Dale Nolte, who heads the U.S. Department of Agriculture federal feral swine management program. “I don’t know of a crop they won’t eat.”
The average male wild pig weighs about 200 lb with some growing to be as heavy as 500 lb. Fences offer little protection against the massive beasts. Hunting and trapping, which once kept the population in check, can no longer keep up with the pigs’ rapid reproduction.
In response, USDA is seeking to reduce the wild pig population that roams in at least 35 states. In January, it launched a national initiative that will attempt to stamp out the pervasive pigs by slipping them bait laced with a fatal dose of sodium nitrite.
Australian scientists pioneered the use of sodium nitrite to kill feral swine. USDA researchers are working in collaboration with the Australians to develop an effective, humane sodium nitrite bait for feral swine in the U.S., says Fred L. Cunningham, a federal scientist in charge of the research arm of the program.
In April, Congress gave USDA $20 million to begin bringing wild pigs under control. The pressure is on for USDA scientists to overcome challenges uncovered in early research and pilot programs that suggest feral swine won’t go down without a fight.
“These things are the ultimate survivors. They can live pretty much anywhere, and they can eat pretty much anything,” says Jack Mayer, a zoologist at Savannah River National Laboratory in Aiken, S.C., who is a technical consultant for the USDA program. But what they’re not so interested in eating is sodium nitrite. The salty taste of the chemical is a turnoff to the pig’s palate.
The curative properties of sodium nitrite are well established for preserving the taste and color of meat. But instead of making bacon, Cunningham and his team are working to develop toxic bait that encapsulates sodium nitrite in a tasty treat that pigs will eat.
Success in the research effort means registering a pesticide with the Environmental Protection Agency for controlling wild swine. But that can only happen after field studies have proven that the toxicant is safe for other animals and effective.
Animal welfare activists, however, are opposed altogether to using sodium nitrite to kill feral swine, calling the method “exceptionally cruel” and urging USDA to end the research.
“Lethal measures are not necessary, but if people insist on killing these animals, poisoning by sodium nitrite should never be an option,” says Stephanie Bell, a casework director for People for the Ethical Treatment of Animals.
In the belly of a pig, sodium nitrite is absorbed into the bloodstream where it reduces oxygen. Without the oxygen it needs to function, the pig faints and dies much as it would through carbon monoxide poisoning, experts say. A lower concentration of an enzyme, methemoglobin reductase, in the pigs’ blood makes them more susceptible to sodium nitrite toxicity than other animals.
“Basically, the animal gets kind of woozy and goes to sleep,” Mayer says. If a wild pig gets a sufficient dose of the substance, he tells C&EN, “it doesn’t wake up.”
“Right now, we do not have any chemical methods that are registered for use” to control wild hogs, Nolte says. He estimates that field studies to optimize use of the toxicant might take three to five years. In the meantime, researchers are developing feeding stations and working on a delivery system that keeps other wildlife from eating the salty bait. They are also investigating chemical contraceptives for controlling the feral swine population.
In response to critics, Nolte reiterates that the goal of the feral swine program is to reduce widespread damage to crops and natural lands.
“Our goal is to reduce damage. Unfortunately, the only way we can do it is to remove the animals,” Nolte says.
“The U.S. has never really warmed up to the use of toxicants to control animals, but we have a national problem, and it’s costing this country a lot of money,” Mayer adds. “You and I are going to pay more money at the grocery store because of the damage that pigs do.”