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Park's wild horses an experiment in birth control

Park's wild horses an experiment in birth control


THEODORE ROOSEVELT NATIONAL PARK — Dan Baker is not like an expectant dad waiting to find out if it’s a boy or a girl. He’s the opposite, hoping to hear that all the pregnancy tests come back negative.

Baker, a research biologist at Colorado State University’s animal reproduction and biotechnology laboratory, is the man in charge of an experimental contraception program in the wild horse herd at Theodore Roosevelt National Park.

There is hope that Baker’s work is productive — not reproductive.

Waiting for results

Within a month, he’ll know if he’s onto something that will have implications far beyond this singular herd in this one park — or if he’s back to square one.

The samples are in, and tests will be run soon. He hesitates to even guess at the results.

“It’s totally unknown. It could be anything between no effects all the way to permanent sterilization. This question has never been answered,” Baker said.

If his experiment works, it could be a new way to control the park’s constantly expanding wild horse herd and possibly the thousands of wild horses on Bureau of Land Management land. The method also could have uses in the control of unmanaged wild dog populations in Third World countries, or simply to suppress fertility in domestic horses, dogs and cats.

Badlands lab

Baker’s work in what he calls a perfect — not to mention beautiful — outdoors laboratory dates back to 2009.

“It’s such a great natural lab out there. The area the horses are confined in is large, but not too large. It’s great landscape, and we can find them most of the time,” he said.

In 2009, during the park’s scheduled wild horse roundup and herd reduction, Baker vaccinated 28 wild horses with GonaCon, a vaccine that has been used to suppress pregnancy in captive animals, not free-roaming wild ones such as those in the park.

The results were poor. Half the vaccinated mares became pregnant and, within three years, they all did.

What they’ve since learned is that, even though the park’s wild horses are in excellent physical condition, with good forage, they carry a big parasite load, which may have prevented the kind of antibody response needed to suppress pregnancy.

“Real world horses get injured, or have fence cuts, and their immune systems go toward those things rather than suppressing the hormones that control reproduction,” Baker said.

Last year, the park conducted another wild horse roundup and that’s when Baker’s research took a step further. The same 28 mares were revaccinated to learn whether a second booster of the same drug would achieve a higher antibody response and improve contraception.

Last month, volunteers collected fecal samples dropped on park ground by as many of the 28 vaccinated mares as could be located.

By measuring the feces for estradiol, a hormone excreted by a fetus, Baker’s lab team will soon know if the revaccination was successful.

“As the fetus matures, the concentration of estradiol gets higher and higher. If it’s 10 (nanograms per gram), they’re not pregnant. If it’s 100, they are. In a couple of weeks, after we’ve looked, if everything’s really high, the study’s over,” Baker said.

The proof will be in the lab, but the mares will also be observed in the spring to verify the actual foaling rate.

Park waiting, too

Blake McCann is the park’s wildlife biologist, a man who prizes science and wildlife equally.

McCann’s hopeful the revaccination works, too, but for reasons that have more to do with the horses, than the science itself.

He’d like to see the park bring to an end the longstanding practice of controlling the wild horse population with controversial helicopter-driven roundups and transport to public livestock sales barns. Instead, if the revaccination controls pregnancy by even 50 percent, McCann said becomes more feasible to also lure the wild horses into a makeshift corral in their own environment and remove small select numbers for sale right there.

That practice would be much less traumatic all around for humans and horses, he said. He plans to conduct a corral trap this year to start learning how and to manage the 142 wild horses currently in the park, a number well above the 40 to 90 population considered ideal.

Some doses of the second vaccine were delivered by dart, which was acceptable for the experiment.

“For research, yes, but to use that as a management tool, we would have to go into an environmental impact statement. Darting animals is not part of our management plan,” McCann said.

Whether through contraception or smaller removals from the temporary corrals, McCann said he does not want to see wild horse numbers return to the all-time high of 200 that were there last year when 103 were culled and sold at Wishek Livestock.

“I don’t want to get to 200 again and do another helicopter roundup. With the corral trapping, we can remove a dozen or so every year and get the young mares out before they become reproductively active,” he said.

That said, McCann said he’s hoping Baker’s work is productive, not reproductive, as it were.

“I would like to see the vaccine be a viable tool. We always have to be adaptable as a situation unfolds. I’m hopeful it’s effective,” he said.

Reach reporter Lauren Donovan at 701-220-5511 or


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