Dr. Jay F. Kirkpatrick believes the key to wildlife population control isn't in culling out the existing population but in addressing its reproduction.
"If you remove them -- if that's your major management approach -- you're not addressing the problem, you're addressing the symptom," he said. "If you attack reproduction, you get to the source of the problem."
That's the approach the Science and Conservation Center has taken in its production of porcine zona pellucida (PZP), the active ingredient in a contraceptive vaccine approved on Thursday by the Environmental Protection Agency for use in horses. Kirkpatrick is one of three people who own and operate the local, nonprofit research laboratory.
Registered under the name ZonaStat-H, it is the first such vaccine approved and registered by the EPA, which recently took over regulatory authority for wildlife contraception, with the exception of zoos, from the U.S. Food and Drug Administration.
The Humane Society of the United States sponsored the registration, partially because it is a non-lethal population control method.
"Killing and culling to solve human-wildlife conflict is becoming less acceptable and fertility control offers the hope of a new framework for human interaction with wildlife," said Dr. Andrew Rowan, HSUS' chief scientific officer, in a news release.
The approval means there's a possibility that demand for the vaccine's use in wild horse control will increase. But the folks at the Science and Conservation Center, on ZooMontana's grounds on the West End, aren't sure by how much.
"We don't know exactly what it will mean," Kirkpatrick said. "We do know it's going to put pressure on our training program."
The center trains people on how to use, handle and administer PZP and can currently put four people through the intensive three-day class at a time.
The center makes a few thousand doses of the vaccine each year. Robin Lyda produces it in a pair of small labs at the center and said it takes about 25 hours over a week to make one batch, which yields 150 to 200 doses.
It's an exact process that involves stripping the membranes and extracting a protein from the eggs in pig ovaries, followed by a series of five filters before processing and determining protein levels and quality.
"You don't want to say, 'Oh, I can finish this next week,'" she said of the production process.
When administered, the animal's immune system attacks the vaccine. Antibodies will then seek out similar objects and bind to its eggs, blocking what Kirkpatrick calls "molecular keyholes," and preventing sperm from fertilizing them.
The center has been producing PZP, discovered at the University of Tennessee in 1972, since 1998 under an FDA experimental use exemption.
In 2011 it was used on about 1,600 free-ranging horses across the U.S., including Montana's Pryor Mountains and the McCullough Peaks area in Wyoming.
A U.S. Geological Survey said the vaccine could save as much of $7.7 million each year in western wild horse management, according to a news release from the center.
However, under the FDA experimental designation, they've also vaccinated deer and more than 85 species in zoos worldwide, including bears, water buffalo, elephants and bats.
"We have no idea how far into the animal kingdom it works," Kirkpatrick said.
In one instance, they managed to reduce a localized deer population by 70 percent without having to shoot a single animal other than with the dart gun used to deliver the vaccine, he said.
Officials with the center like to tout that it's the only wildlife non-barrier contraceptive that doesn't interfere with the animals' endocrine system and wears off after a few years without revaccination.
But they also want the people administering it to understand the effort that goes into production, the science behind it and the value of the vaccine.
"We want to train people to see how we make it and how much work goes into it," Lyda said. "We want them to understand that you don't just go and take a wild shot at a horse with this."
Kirkpatrick said he's excited, and a little surprised, at the impact a little three-person lab tucked away in southcentral Montana can have on an international scale, especially in light of Thursday's EPA approval.
"It's amazing," he said. "We're a boutique operation that's put a worldwide footprint out there."