Birth control for ponies? A dart gun and a good aim


Assateague Island -- Good science can be messy sometimes.

Horse researcher Jay Kirkpatrick is trudging through marsh grass that looks more like a rice paddy, it's so wet. And that's not the worst: He's collecting urine samples from the wild horses of Assateague, scooping up water and whatever into little vials.

And he's doing it happily.

"The beauty of this is overwhelming," he tells a reporter along for the day.

Although it is indeed a spectacular, sunny day (wet feet and horse urine nothwithstanding), he's referring to the contraceptive vaccine he developed for the herd on the Maryland side of Assateague. The National Park Service would like to bring the herd size down to 150 animals from the present 170. Mr. Kirkpatrick has developed a contraceptive vaccine that can be administered remotely: It's put in an orange dart, and he shoots the mares with it from a distance.

"You don't interfere with her endocrine system or particular behaviors," he explains. The mares still mate with the stallions; they just don't get pregnant. The steroid hormones don't disrupt the food chain on the island, either: "This is protein and protein can't go through the food chain. The stomach breaks it down into amino acids."

The once-a-year vaccine, now in regular use on the Maryland herd, represents nearly 20 years of work for Mr. Kirkpatrick and his partner.

The vaccine in the darts is scientifically complex but the simple explanation goes like this: It's a kind of pig protein that causes the mares to make antibodies that change the shape of their eggs, so that sperm can't fertilize them.

On this day of taking urine samples to be sure the vaccine is working properly, Mr. Kirkpatrick is surveying a band of horses with pride that could pass for paternal.

He is standing at Singer Point on Assateague, watching four mares, a foal, two young stallions and, off at a distance, a watchful stallion whose band this is.

"They're totally on their own," he says softly. And so they are, munching grass as the sun sprinkles diamonds on bay waters and the Atlantic rumbles gently in the distance.

Mr. Kirkpatrick's vaccine is being used effectively to bring the Maryland herd size down to the 150 desired by the National Park Service. After developing it, he gave the patent to the National Humane Society, because he didn't want it to be misused.

"I think there's a lot of moral implications with this," he says. "We're not going to contracept wolves in Alaska so there are more caribou for hunters.

"There are three steps in wildlife contraception. One, does the agent work? Two, can you deliver the agent under field conditions? Three, can you show a population effect?"

For his vaccine, called PZP, the answer to all three is yes. And Mr. Kirkpatrick, although pleased, still marvels that it actually works.

"Basically the whole herd is now infertile," says Carl Zimmerman, a resource management specialist at the Assateague Island National Seashore in Maryland. He says the only exception is a small group of mares that are part of an ongoing study on contraception.

"Over the years, everything else we did got sidetracked, tossed by the wayside," Mr. Kirkpatrick says reflectively. Funding to keep going was hard, he said. Money for the program came from a variety of government and private sources.

"The other difficult thing was maintaining the persistence over a lot of years of no progress," he says. "There were a lot of years where I thought, 'I'll just walk away,' but I kept coming back."

And it was clearly worth the struggles.

"The Assateague herd is the model for everything. . . . Everything we did here was right," he says.

Behind him, the horses shift slightly and continue grazing, undisturbed.

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