Wild horses, other animals benefit from drug

May 22, 2015 - From a small, unobtrusive building in west Billings comes a product that travels across the U.S., and into Canada, Romania and Hungary, for the benefit of wild animals, including the McCullough Peaks mustangs.

Reproductive Physiologist Jay Kirkpatrick, PhD, and his two colleagues produce porcine zona pellucida (PZP) at The Science and Conservation Center. Last year’s output numbered 4,000 doses.

PZP is a contraceptive used to manage populations of wildlife, mainly wild horses but also bison, elephants and urban deer, Kirkpatrick explained recently to a delegation from the Friends of a Legacy. FOAL is an advocacy group for the McCullough mustangs and supports the use of PZP to control herd numbers and avoid roundups, which are costly, disrupt social structures and sometimes cause fatalities and only serve as temporary fixes.

“With all creation, there’s a problem of overpopulation,” FOAL President Warren Murphy said. “An excellent way to address this in nature is through the potential use of PZP.”

On her recent second tour of the Science Center, FOAL Executive Director Marion Morrison said, “Again it affirmed that PZP is the best answer we have for managing wild horse herds on finite lands.”

‘Titanic’ policy

The 1971 Free-Roaming Wild Horse and Burro Act didn’t delineate the administration of an adaptable, fecund species that was dumped onto the Bureau of Land Management.

“We gave the BLM the keys to the Titanic,” Kirkpatrick said.

The BLM’s adoption program for wild horses, which initially functioned as a way to reduce herds, was soon outpaced by reproduction. That situation was explained in 1971 to Kirkpatrick, then on a college faculty, by two BLM employees concerned about the anticipated explosion of wild horse numbers.

“They told me, ‘In 10 years, we and the horses will be in big trouble,’” he said, because adoption isn’t a solution. “It hasn’t worked, it isn’t working, and it won’t work.”

The encounter led Kirkpatrick to investigate PZP. He figured if people spay and neuter cats and dogs, fertility control could impact certain wild animal populations.

“Historically we treated the symptoms” of too many horses, symptoms such as range degradation, he said. “The problem is reproduction.

“There are really only two choices for wild horse management – roundups and removal or fertility control. There are no other choices.”

Roundups ‘self-defeating’

Avoiding roundups, Kirkpatrick said, avoids public protest, massive genetic loss and compensatory reproduction, which means birth rates typically increase when populations plunge. Kirkpatrick cited records from the McCulloughs showing a growth rate of 14.8 percent per year over 39 pre-contraceptive years. When roundups began, the horse herd grew 26-58 percent annually after each removal.

“It’s self-defeating,” he said of management by roundup.

Furthermore, roundups are costly – $2,165 per horse by helicopter and $1,400 per horse by water or bait trap – according to records from the Pryor Mountain mustangs, Kirkpatrick said. In addition, roundups result in horses that BLM places into long-term holding.

At present, about 50,000 horses reside in long-term holding, which costs BLM $30 million per year, he said. Over a horse’s life, the tab will run $49,000 per head. Already, BLM faces an annual bill for the wild horse program at more than $75 million.

A pig foundation

“We don’t sterilize with fertility control. We delay reproduction with fertility control,” Kirkpatrick said.

Such control worked to manage the herd size on Assateague Island, located off the coast of Virginia and Maryland and managed by the National Park Service. Research indicated a 95 percent efficacy rate of PZP, based on 1988-2006 data. Further, there were no effects on future pregnancies, on social behavior or on reproductive functions.

PZP was introduced to the McCullough mustangs on a regular basis in 2011, where similar success continues. The herd size hovers around 140, close to the ideal size identified by BLM, while the annual growth rate is about zero.

The doses are administered remotely through darting by a team required to participate in a 2½-day training at the non-profit science center, according to Science Center protocol. Chief Operating Officer Kimberly Frank ships the vaccine only to trained individuals.

That one facility in Billings – the sole source for the vaccine and distributed nationally and internationally – impressed Murphy. Also impressed by the dedication of the staff of three who create PZP, he said, “These people are passionate about doing this.”

Morrison echoed those ideas.

“It amazes me that the PZP provided out of this office by three people for population problems goes all over the world,” Morrison said.

To make PZP, Chief Scientist Robin Lyda starts with pig ovaries purchased from slaughterhouses, 350-400 pounds per year at $15 per pound. The eggs are extracted and put through filtering processes. Each batch is numbered and subjected to quality control.

Vaccine’s effectiveness

“The purity of the vaccine is absolutely critical,” Kirkpatrick said. “It’s the only non-barrier contraceptive that operates outside the endocrine system.”

The product goes into a freezer set at minus-43 degrees. The Science Center charges $24 per dose or about 60 percent of the cost.

“We rely on philanthropy to keep us going,” Kirkpatrick said.

Delivery of the vaccine relies on darters. When a dose enters a mare, it triggers antibodies that alter the membrane around her ovaries and block fertilization. Prior to the spring breeding season, a 2-year-old mare receives a vaccine and booster at age 2, gets another dose at ages 3 and 4, allowed to have a foal, and then treated for the rest of her life. The mare makes a memory of the vaccine, so subsequent shots have a more robust reaction, he explained.

Kirkpatrick said along with training, the darters must keep detailed records and share them with the Science Center. In addition to controlling herd size, the program improves the mares’ health. Because the mares are not delivering every year, the program increases their longevity, and decreases foal mortality.

“Life gets better for those horses,” he said.

Originally published in the Cody Enterprise on May 22, 2015

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