Study in North Dakota explores fertility control in mustangs

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At Theodore Roosevelt National Park, free-roaming horse herds share space and resources with the park’s native wildlife population, which includes bison, elk, bighorn sheep and pronghorn. Photo: Marlylu Weber, North Dakota Badlands Horse Registry)
At Theodore Roosevelt National Park, free-roaming horse herds share space and resources with the park’s native wildlife population, which includes bison, elk, bighorn sheep and pronghorn. Photo: Marlylu Weber, North Dakota Badlands Horse Registry)

Wild horses in North Dakota are being dosed with a dart-delivered contraceptive, GonaCon, in the first study examining revaccination in free-ranging mustangs.

The issue of fertility control in wild horses has divided wild horse advocates. While some see it as a potentially effective and humane way to control numbers, others are vehemently opposed, worried about potential health risks and the effects of the drugs on behaviors and herd dynamics.

The project, in Theodore Roosevelt National Park, is one of two Colorado State University (CSU) studies examining elements of wild horse contraception in the US western rangelands.

A team led by researchers from Colorado State University’s Animal Reproduction and Biotechnology Laboratory were trekking through the badlands of North Dakota this week to deliver the GonaCon doses.

The project stems from the team’s success studying GonaCon in both captive and free-roaming elk in Rocky Mountain National Park in 2005. That work sparked an interest to test the drug on horses as part of a study launched in 2009 at Theodore Roosevelt National Park.

Two researchers from the university, Dan Baker and Terry Nett, were awarded a five-year Bureau of Land Management (BLM) grant to find an optimum GonaCon revaccination schedule to suppress fertility in wild horses long-term.

Wild horses at Theodore Roosevelt National Park. Photo: Marlylu Weber, North Dakota Badlands Horse Registry
Wild horses at Theodore Roosevelt National Park. Photo: Marlylu Weber, North Dakota Badlands Horse Registry

The team has received about $US160,000 in funding for the first two years.

“We hope this study will help cut down on the amount of scheduled roundups the park has to do – and perhaps they won’t have to do them at all if the vaccine proves effective and we find the correct dosing schedule that works for the park’s herds,” said Baker, who is an affiliate faculty member in the university’s Department of Biomedical Sciences.

“That’s the point we want to get to, but no-one has ever done this before.”

In the second project, researchers are in the early stages of work to develop and test a new contraceptive vaccine that could permanently sterilize a mare after a single dose, circumventing the challenges of administering repeated doses for long-term fertility control.

The work is being led by Douglas Eckery, an affiliate faculty member in the university’s Animal Reproduction & Biotechnology Laboratory (ARBL) and a research physiologist/project leader for the U.S. Department of Agriculture’s National Wildlife Research Center, and Jason Bruemmer, an ARBL faculty member and professor in the Department of Animal Sciences.

They pair were awarded a four-year grant of about $US800,000 from the BLM to conduct the study.

Jason Bruemmer is an animal sciences professor working to develop a new type of long-lasting contraceptive for use with wild horses.
Jason Bruemmer is an animal sciences professor working to develop a new type of long-lasting contraceptive for use with wild horses.

“No one has looked at this in horses yet,” Eckery said. “It’s brand new and could potentially offer a more permanent solution that current vaccines don’t.”

The Wild Free-Roaming Horses and Burros Act of 1971 gave the BLM and the U.S. Forest Service the task of managing wild horse and burro populations on public lands. Formally designated Herd Management Areas under the act have appropriate management levels – the number of horses considered appropriate to promote healthy conditions on the range.

On Western public rangelands overall, the appropriate management level is 26,715 free-roaming horses and burros.

However, according to the most recently published population estimates from the BLM in March 2015, the current population was 58,150 horses and burros. Projected estimates for 2016 are expected to be 15-20 percent higher.

Horses and burros that exceed the appropriate management level are removed in periodic roundups, followed by the adoption, sale, or placement of removed animals into long-term holding facilities.

The roundups have proved controversial, with some wild horse advocates arguing the musters are inhumane and risky to the horses. They have attacked the escalating costs of the strategy, and believe other strategies should be used to control numbers on the range. However, they cannot agree whether fertility control is the right management tool to use.

That said, few disagree that the current management strategy is costly. In 2015, the BLM appropriated more than $US77 million to manage free-roaming horse and burro populations, with 65 percent of that budget going towards the expense of supporting unadopted horses and burros removed from the range.

Because Theodore Roosevelt National Park’s free-roaming horses are on National Park Service land, they are not protected under the 1971 law.

“But we’re affected by that policy,” said Blake McCann, the park’s wildlife biologist. “The way horses are managed on other public lands drives a lot of the expectations for us, so we’re trying to find practical solutions to manage the herd by evaluating a number of different techniques — and we’re wielding science to inform that process.”

Wild horses typically form bands of six to 10 mares and one stallion. Photo: Marlylu Weber, North Dakota Badlands Horse Registry
Wild horses typically form bands of six to 10 mares and one stallion. Photo: Marlylu Weber, North Dakota Badlands Horse Registry

The park’s native wildlife population includes pronghorn antelope, elk, bighorn sheep, and bison. In order to preserve range quality, the park’s goal is to manage for up to 90 free-roaming horses. There are now about 150 horses in the park, and many are involved in the GonaCon study.

A longtime park volunteer and technician for the university’s research project, Marylu Weber, created the North Dakota Badlands Horse Registry with her husband in 2009.

The nonprofit adoption program partners with the park to assist with low-stress captures and with finding pre-screened homes for removed horses, thus avoiding the need for public auctions.

“Without intervention, it would be difficult to keep up with the captures and adoptions of so many horses,” Weber said. “CSU’s research is very important to the management of the park’s horses and has huge potential to impact wild horse management all over the world.”

Baker and Nett’s research team now knows all of the park’s horses by name and can spot individuals from a mile away by their coloring and markings.

Weber, who has been keeping track of the park’s horses since she began riding there in the 1980s, helps train new technicians on how to find and identify the horses in the study, take measurements, and collect data.

As the team hikes the park this week to locate specific mares, they will come within 25 yards of each to administer GonaCon using a novel remote syringe dart-delivery technique that the university’s team perfected. This safe and effective method of administering the vaccine, which interrupts ovulation, does not require roundup efforts or interfere with pregnancy.

Colorado State University researcher Dan Baker, left, and Theodore Roosevelt National Park wildlife biologist Blake McCann prepare syringe darts to deliver a contraceptive vaccine.
Colorado State University researcher Dan Baker, left, and Theodore Roosevelt National Park wildlife biologist Blake McCann prepare syringe darts to deliver a contraceptive vaccine.

When darted, the horses tend to briefly look up and, with a swish of their tails, return to grazing; the syringes fall to the ground and are retrieved by technicians.

The team will return to the park in September to deliver one more round of booster vaccines to a group of mares. They will then spend three years monitoring foaling rates to see how well the vaccine is working and which vaccine schedule is most effective.

Baker and Nett hope this week’s booster vaccines will last for multiple years.

“GonaCon is already being used, but we need to figure out how to make it work best,” said Eckery, whose laboratory at the National Wildlife Research Center developed and continues to make the vaccine.

Kathleen Eddy, a doctoral candidate in the Department of Biomedical Sciences, is working in Nett’s endocrine lab to help the team determine how much of the pregnancy hormone estradiol is in mare feces collected from the park.

“This could be a good indicator for determining not only if a mare is pregnant, but also how far along she is,” Eddy said. This means the team could potentially complete sampling of all of the study’s mares in one week.

The research team devised a remote syringe dart-delivery technique to administer contraceptive vaccine.
The research team devised a remote syringe dart-delivery technique to administer contraceptive vaccine.

“She is making a major contribution to the project,” Baker said of Eddy. “If this works well, we may not need to continue foaling measurements each spring, which can be costly and time-consuming.”

Eckery and Bruemmer, who are leading the separate research project, are in the early stages of their effort to develop and test a new contraceptive vaccine that could potentially disrupt follicular growth, deplete egg reserves, and result in the permanent sterility of mares.

“I’ve been interested in the topic of wild horse management for a long time, but I never thought I would get the chance to work on something that could have such a vast impact,” said Kelli Davis, a master’s student in the Department of Animal Sciences who recently began working on the project. “I’m excited to see where this research takes us.”

The issue of free-roaming burros is of equal concern, yet far less research has been done on those populations. Baker, Nett, Eckery, and Bruemmer are discussing how they might investigate the effects of contraceptive vaccines in burros as well.

“The BLM is aware of and sensitive to the need for better long-term planning for management of wild horses and burros,” said Paul Griffin, research coordinator with the BLM’s wild horse and burro program.

“These CSU projects are very promising and exciting for us because they potentially offer contraceptive options that would be long-acting and easy to deliver, and may provide us with great solutions to reduce the population growth rate in ways that are consistent with the animals’ protected status under the 1971 law.”

A band of wild horses at Theodore Roosevelt National Park. Photo: Marlylu Weber, North Dakota Badlands Horse Registry
A band of wild horses at Theodore Roosevelt National Park. Photo: Marlylu Weber, North Dakota Badlands Horse Registry
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