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BLM looks to improve fertility controls for wild horses

Population of Spring Creek Basin Herd is managed by a fertility control program. (Courtesy of TJ Holmes, file)
Use of fertility darts have controlled population of Spring Creek Basin herd for 11 years

The Bureau of Land Management is seeking public comments for three new proposed research projects focused on developing better, longer-lasting fertility control methods for managing and protecting wild horse herds on public land.

Without intervention wild horse herds typically grow very quickly – doubling in size every four years, a BLM news release said.

About 82,000 wild horses and burros were roaming public lands in designated herd management areas as of March 2022, which is more than three times the appropriate herd size, according to BLM statistics.

An overpopulation of wild horses can degrade important ecosystems and lead to starvation and/or dehydration.

The BLM reports that existing fertility control methods are short-lasting and require multiple doses, which limit their effectiveness as a management tool. Longer-lasting fertility control methods would be potent tools to better control herd growth and protect animal and land health.

The population of Spring Creek Basin wild horses in Disappointment Valley has been effectively controlled by a fertility-control dart program that uses Porcine Zona Pellucida vaccine for more than 10 years, said Mike Jensen, a range specialist who oversees the herd for the BLM Tres Rios Field Office.

The program has kept the herd to 75 horses, which is below the maximum of 80 allowed within the management area. Controlling the birthrate has prevented the need for roundups to reduce numbers.

Jensen said the longer-lasting fertility vaccines being studied would be helpful and reduce costs and labor.

“Our program has been successful. I’d say there are a lot of logistics, and we have limited resources, so it would be advantageous and less labor intensive if the vaccines were effective for more than a year or multiple years,” he said.

The BLM has two staff members and a volunteer who are certified to administer the fertility control.

A dedicated group of volunteers with the National Mustang Association of Colorado are also relied on by the BLM to help manage and support the herd, Jensen said.

“Without them, it would be difficult on our limited staff,” he said.

Two of the proposed BLM research projects would quantify the effectiveness of vaccines for preventing pregnancies in wild horse mares. One would build on previous research to develop a long-term one-dose vaccine, and a second would test a fertility control vaccine that has some preliminary studies in horses and other animals. The third proposed research project would test specialized intrauterine devices in a wild horse herd management area on public lands.

All of the proposed projects would be required to follow BLM’s animal welfare policies when handling wild horses. Also, researchers would follow guidelines set by their respective Institutional Animal Care and Use Committees.

The BLM has analyzed the potential impacts of the three proposed research projects in a draft environmental assessment as required by the National Environmental Policy Act. Instructions to access the draft analysis and to submit a comment can found by visiting the BLM’s ePlanning page. The deadline to submit comments is Aug. 22.

The BLM identified the development of safe, effective and long-lasting fertility control methods as a top research priority in its 2021 Wild Horse and Burro Strategic Research Plan. The three proposed projects were submitted to the BLM by two federal agencies, four universities and other organizations in response to a solicitation seeking new research projects in November 2021.

Spring Creek Basin herd update

This year, 18 to 20 mares in the Spring Creek Basin herd were given the fertility control treatment, which took about six weeks, Jensen said.

Mares not selected for breeding get a vaccine dart once per year. If it is the first time for a mare to be treated, two shots are required, with the second after 30 days.

It takes time to find the preselected horses for fertility control, and bad weather can be a factor, Jensen said. Officials traverse the backcountry for days to find and reach the right horses for the treatment.

“A lot of days, we don’t have the opportunity to dart one,” Jensen said.

Water catchment systems have been installed for wild horses in the Spring Creek Basin herd in Disappointment Valley. (Jim Mimiaga/The Journal)

Officials must get within 30 yards of the animal to effectively deploy darts. Windy conditions make the shot more difficult.

The darts are designed to kick back out of the horse, and can be recovered to verify the dose was injected.

The Spring Basin Herd PZP program started after a 2011 roundup that included use of helicopters, a tactic that has been controversial. Since then, no roundups have been necessary, Jensen said.

“We were able to slow the birthrate down for the past 11 years,” he said.

Three or four foals are born every year, down from 12 to 15 each year before the fertility dart control program was put in place.

The goal is not to eliminate reproduction. Each mare is allowed to have at least one foal to sustain herd health and genetic diversity.

The natural death rate also factors into managing herd population and use of the PZP program.

“Some years, the natural death rate was the same as the birthrate,” Jensen said.

A forage production study showed the 22,932-acre Spring Creek Basin management area could support additional wild horses.

In 2020, the appropriate management level was increased to 50 to 80 horses on the range, up from 35 to 65. They consume 35% of available range, which allows forage resources for other wildlife.

Last fall, three mares were introduced from the Sand Wash Basin to improve genetic diversity.

Rainwater catchment systems have been installed in strategic locations on the range, and a fourth is being installed this year.

The systems have storage tanks and managed water delivery to the trough. When other ponds on the range are full, the water catchment systems shut down water to the trough.

Monsoon rains this year have kept ponds at good volume, and the range is green and growing, Jensen said.

The Spring Creek Basin herd management area is relatively small and more accessible for effective fertility control. Longer-lasting vaccines would help manage larger herds on hundreds of thousands of acres, Jensen said.

In July and August, the BLM rounded up hundreds of horses in the Piceance-East Douglas herd management area. Helicopters were used in the roundup.

jmimiaga@the-journal.com

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