CSU researchers team with federal agencies to find better ways of managing wild horse herds

A team led by researchers from Colorado State University’s Animal Reproduction and Biotechnology Laboratory is trekking through the badlands of North Dakota this week to dart-deliver a contraceptive vaccine called GonaCon to a select group of mares. This marks the first time that revaccination with GonaCon has been studied in wild horses.

The project, in Theodore Roosevelt National Park, is one of two CSU studies underway that aim to provide safe and humane solutions to help rein in wild horse populations in the West and reduce the need for roundups, sales, and adoption programs.

Dan Baker, an affiliate faculty member in the Department of Biomedical Sciences, and Terry Nett, an ARBL professor in the Department of Biomedical Sciences, were awarded a five-year Bureau of Land Management grant to find an optimum GonaCon revaccination schedule that would suppress fertility in wild horses long-term. The team has received about $160,000 in funding for the first two years.

Vaccine was successful with elk

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

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

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

In a second project, a research team is working to develop and test a new contraceptive vaccine that could potentially result in the permanent sterility of a mare after a single dose, thus circumventing the challenges of administering repeated doses for long-term fertility control. Douglas Eckery, an affiliate ARBL faculty member in the Department of Biomedical Sciences and 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, were awarded a four-year BLM grant of about $800,000 to conduct the study.

“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.”

A complicated and costly dilemma

Jason Bruemmer, Equine Reproduction Laboratory, Animal Sciences, Colorado State University
Jason Bruemmer, an animal sciences professor, is working to develop a new type of long-lasting contraceptive for use with wild horses.

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. Free-roaming horses in the U.S. are commonly referred to as “wild,” but in biological terms they are “feral” because they have descended from domestic animals that were released or escaped captivity.

“To promote healthy conditions on the range, the BLM determines what it calls the appropriate management level, which is the number of wild horses and burros that can thrive in balance with other public land resources and uses,” said Paul Griffin, research coordinator with the BLM’s Wild Horse and Burro Program.

On Western public rangelands overall, the appropriate management level is 26,715 free-roaming horses and burros. But according to the most recently published population estimates from the BLM in March 2015, the current West-wide population was at approximately 58,150 horses and burros. And projected estimates for 2016 are expected to be 15 percent to 20 percent higher. With virtually no natural predators, free-roaming horse populations can double every four years.

“Horses are primarily grazers, foraging year-round, and have a slightly higher food intake for their weight compared to ruminants, such as bison and elk,” Griffin said. “They compete with native wildlife for food resources and water and there is concern of them overgrazing, particularly in sensitive habitats, like riparian areas or areas near streams or seeps.”

Management is based on ecosystem health

Free-roaming horses and burros that exceed the appropriate management level are to be removed to protect the health of the animals and the lands they live on. The most commonly used methods of population control are periodic roundups, followed by the adoption, sale, or placement of removed animals into long-term holding facilities. But these processes are costly and resource intensive. In addition, advocacy groups fear that some of the removed animals end up in slaughterhouses, which violates BLM policy.

In 2015, the BLM appropriated more than $77 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.”

Other large mammals compete for forage

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

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 CSU’s GonaCon study.

Marylu Weber, a longtime park volunteer and technician for the CSU research project, 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.”

Experts combine forces to provide new tools

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 1980’s, 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’ll come within 25 yards of each to administer GonaCon using a novel remote syringe dart-delivery technique that the CSU team perfected. This safe and effective method of administering the vaccine, which interrupts ovulation, does not require roundup efforts or interfere with pregnancy. 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 lab at the National Wildlife Research Center developed and continues to make the vaccine.

Looking for better long-term management

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

“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 with Eckery and Bruemmer. “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,” Griffin said. “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.”