Horse tales

Volunteers spend their days giving birth control vaccines to wild mares

Wild horses stampede up a hill in the Virginia Range.

Wild horses stampede up a hill in the Virginia Range.


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On Veterans Day morning, three women were waiting for me in the parking lot of a Maverik gas station in Carson City. Deb Walker, Elena Sullivan and Nancy Kilian wore matching shirts with the words “Nevada Wild Horse Darting Team” printed across the back and the logo of the American Wild Horse Campaign emblazoned on the front.

AWHC—a nonprofit horse advocacy and management organization—signed an agreement in April with the Nevada Department of Agriculture to run a fertility control program on the region's beloved Virginia Range horses, of which there are more than 2,000. Sullivan, Kilian and Walker—who's also AWHC's Nevada field representative—are among 14 people who volunteer their time to the program. On this day, they'd also volunteered to take me along to see how it's done.

With greetings out of the way, we piled into Sullivan's Jeep Wrangler—also adorned with AWHC logos on magnets stuck to its front doors alongside the words “Northern Nevada Virginia Range Mustang Fertility Control Program.” In the back, they'd stashed the components to mix up birth control vaccines, syringe darts to deliver the medications and CO2-powered rifles from which to fire them.

Learning the ropes

Porcine Zona Pellucida, called PZP for short, is an immunocontraceptive—meaning it works by causing an immune response. Having reported on wild horses for years, I was already familiar with PZP. For those who aren't, here's a brief explanation.

PZP has been used as a wildlife birth control for decades—mostly on zoo animals and horses. And, yes, if the word “porcine” tickled something in the back of your mind, it is in fact made with the help of pigs. And if the “zona pellucida” part didn't ring a bell, that's all right. It's simple. Zona pellucida is a membrane that surrounds the eggs of all mammals. Certain proteins in the membrane act as the sperm receptor. When these proteins are harvested from pigs and used to vaccinate other wildlife, like horses, it spurs the production of antibodies that attach to the vaccinated animal's own zona pellucida, blocking sperm.

To learn about PZP and its application in greater depth, my three companions had, at various times, each traveled to the Science and Conservation Center in Billings, Montana, to receive training and become certified to administer the vaccine—a federal requirement.

Kilian went through training before Sullivan and Walker, more than four years ago, and has since administered more than 500 doses of PZP to mares through fertility control programs done in cooperation with Bureau of Land Management and the NDA. Before we headed into the foothills of the Virginia Range to look for more horses to vaccinate, Sullivan wanted to stop by the nearby Eagle Valley Golf Course to look at a project that typifies the efforts of horse advocates in the region.

“The great thing about the volunteers is they represent several organizations all with the same commitment, and they all do different things,” said Walker as we pulled up to a gated fence running along the north side of the golf course property.

Kilian and Sullivan are both members of another wildlife advocacy group called VRWPA—Virginia Range Wildlife Protection Association—which spearheaded the fence project. Other volunteers in the fertility control program are members of different groups. All told, there are around a dozen such organizations in the region. They work together to fundraise for projects like the fence, which features a springloaded gate that prevents horses from pushing it open to access the golf course greens and surrounding homes and businesses. Sullivan explained that efforts to get the fence constructed had been ongoing for years.

Nancy Kilian lines up her shot to deliver a dose of PZP to a mare.


“Yeah, there have been people … who've been trying to get it fenced here for about 10 years,” she said. “And each time they go to the city, the city says, ‘Well, we don't have any money.' … It happens year after year. Some years worse than others, where the horses come down onto Highway 50 or Arrowhead or the businesses.”

The project cost for the fence was around $14,000, and VRWPA is still looking for ways to recoup the total costs, though Carson City officials have agreed to pay for its maintenance hereafter. VRWPA had located a donor who'd offered to pay for half of it, but he died—and they're unsure if his widow will follow through with the donation. Nevertheless, Kilian said, the groups' members are pleased that the fence is in place.

After checking it out, we hopped back in the Jeep to head beyond the fences and into the Virginia Range in search of horses.

Riding out

“A lot of times there's horses sitting near Linehan [Road],” said Sullivan from the driver's seat. “If I didn't find anybody at Linehan, I figured we'd go up by the Bathtubs.”

The Virginia Range horses are spread out across a nearly 500-square-mile area that includes the Reno, Carson City, Silver Springs and the Fernley area. Sullivan and Kilian, who often go out together in search of horses to immunize, patrol and manage the ones who roam the Mound House area and are familiar with all of the little dirt roads and ATV trails that crisscross it. They designate different areas by name to help them keep track of where they've spotted horses.

“We actually have one area called Creepy Canyon—because if we identify them by names, you can tell someone else, ‘I saw the horses here,'” said Sullivan. “They call it Creepy Canyon because one of the darters once saw some coyotes there tearing up some other animals.”

Creepy Canyon, the Bathtubs and Linehan are just a few of these place names. After leaving paved roads behind, it wasn't long before we spotted horses in the first area Sullivan had surmised they might be.

“That's Speckles and Bits, so this is Lieutenant's band,” she said, pointing to a group of horses grazing on the foothills up the road from us. “That little chestnut is Rue.”

Sullivan could tell it was Lieutenant's band of horses even from a distance because it has two distinct roans—beautiful animals with light bodies and dark manes. Lieutenant, by the way, is the stallion of the band—a name given him by the volunteers. They name all of the horses and call each band after the stallion that leads it.

“You can take pictures of them, but we don't need to dart them—because we've already darted them,” Sullivan said. “But usually we'll stop and try to ID them and make sure they're all there—that nobody's missing and no one is extra. And then we'll move on to the next band.”

Two horses eye me warily as I take their photo.


As we drove up the dirt road toward the horses, I expected them to get a bit antsy, to perhaps alter the course of their grazing—but they maintained their path, and we got close enough to see each horse clearly. When we stepped out of the Jeep, Sullivan and Kilian showed me how they keep track of the horses and which among them has been vaccinated.

For Kilian, this is done with binders. Inside, tabs bearing the names of stallions are used to designate individual bands, with pages in between each containing information about the band's individual horses, including their ages, markings, sire and—for mares—whether or not they've been vaccinated and when. She has two full binders just for horses in the Mound House area. Sullivan has access to the same information using a tablet equipped with a database her husband built to keep track of horse bands all over the Virginia Range.

“A lot of people are under the impression that we've darted every single mare or don't know which ones we have or haven't,” Sullivan said.

But keeping meticulous records helps them avoid this—and listening to Sullivan and Kilian talk, it was clear this method works. They knew each horse in the band and when the mares would need vaccinations and booster shots. Since none did, it was time to head back to the Jeep and go in search of more.

Hoofing it

Driving around the southern part of the Virginia Range, we saw coyotes and golden eagles but no other horses at all for the next few hours. We checked Creepy Canyon (true to its name) and the Bathtubs—so called because three old bathtubs are lodged into the earth to create troughs where a spring bubbles up from the ground.

“This is reality,” said Walker as we drove west on more dirt roads. “This is how it's done.”

“Some days you come out here and there are tons of horses,” Kilian affirmed. “Other days it's like, where'd they go?”

“And then in the spring there will be, like, 200, and it's like, ‘oh!'—trying to ID them,” Sullivan said.

“Yeah they all get together to have their babies,” Kilian added. “I think they feel safety in numbers.”

Volunteers like Kilian and Sullivan often spend four or five days a week out checking for mares who need vaccinations and boosters, but during the spring this schedule picks up for all of them. It'll pick up in January, too, when many of the range's mares will need booster shots of PZP.

Nancy Kilian mixes up a dose of PZP prior to darting a mare.


“Once we give them their initial primer, we like to wait two-plus weeks for the immune response,” Walker said. “Then we get them [with a booster] … at about two weeks, two-and-a-half weeks.”

For the average mare, the booster increases PZP efficacy from around 93 percent up to 97 percent.

“And then at about seven or eight months you start boosting again—just to keep the numbers high, because if we don't keep the numbers high there's just that much more chance they'll get pregnant,” Sullivan said, adding that when January booster time rolls around, she and Kilian will likely be out on the range six days a week.

Champing at the bit

As the morning turned to afternoon, we continued driving the winding back roads of the Virginia Range, finding some horses but none that needed vaccinating.

When we happened upon a band of just three—a stallion, a mare and their filly—Walker explained that the baby would soon need vaccinating.

“We like to get the 11-month-old fillies, so they can't be bred immediately,” she said. “And we like to get the pregnant mares, so they're inoculated and then, after they have foals, they're protected against conception. They'll still come into foal heat. The stallion will still breed them. They just won't conceive.”

“The nice thing about birth control is the mares get a chance to grow to a healthy size and weight,” Kilian said.

After leaving behind the band of three—comprised of “Woody,” “Fern” and little “Alder”—we encountered a group of bachelor horses. These young stallions, Sullivan explained, had been kicked out of their sire's band—a natural process—but were palling around together as they'd yet to form bands of their own.

“We try to ID the bachelors too—because they become the next year's stallions,” Sullivan explained.

But these young stallions were on the move not long after we stopped, making their way farther up into the hills where we were headed next.

Elena Sullivan (left) and Deborah Walker watch wild horses grazing in the distance.


Hold your horses

As the afternoon wore on, we managed to find two other bands of horses—another with mares whose vaccinations were current, and one on a distant, opposite hillside overlooking Washoe Valley. We could see no roads snaking across the valley between us, but Sullivan explained that we wouldn't have been able to vaccinate the horses we'd spied even had we been able to get to them. They were on private property, and while it's possible for the volunteers to get permission from land owners, it's not as simple as just asking. It's a process that requires obtaining assessor's parcel numbers for properties and allowing the NDA to cross check these to ensure that permission was obtained from their rightful owners.

By the time we were ready to break for lunch, I was beginning to think I wouldn't get to see the AWHC volunteers administer any birth control vaccines that day. But Walker, Sullivan and Kilian had one more trick up their sleeves.

Before taking me to a piece of private property in Paradise Valley, the women explained two things. First, it's illegal to feed wild horses on BLM or private property for the most part—but that was what was happening here. And, second, it wasn't illegal in this case. It was an NDA-approved effort to use a large swath of private land as a place to feed the horses on the edge of Paradise Valley in an effort to keep them out of the neighborhoods closer to the highway. Its goal, they said, was to move the horses slowly over time back up into the foothills.

When we arrived, the property owner asked me to please not reveal the location of her land. It's hard enough, she explained, to keep people who want to see the horses at bay. And I could immediately see why. There they were—hundreds of Virginia Range horses all in one place.

When Kilian and Sullivan donned bright green vests and walked right out among them, my pulse quickened at the sight of two small women in the midst of so many huge animals. But this feeling faded quickly as I watched the pair identify mares and stallions by name. Soon, they'd picked out half a dozen mares in need of vaccinations and boosters and were headed back to the Jeep to prepare their doses.

The process of preparing PZP for injection is fascinating. The vaccine itself is kept frozen in tiny vials. It's thawed quickly in warm hands and then mixed in a separate vial with an adjuvant—a substance that helps create a stronger immune response. When the vaccine is ready, it's contained inside a thick-needled dart and loaded into the CO2-powered rifles.

I watched as Kilian prepared to take her first shot at a mare eating hay with her band near the edge the property. With a range finder she determined the mare was 22 yards off. Using this information and a simple mathematical formula, she set the pressure on her rifle and then lined up her shot.

When she fired it, the sound wasn't much louder than that of an arrow shot from a compound bow.

The dart flew quickly and found its mark. I flinched as the mare whinnied and began to trot, causing her band to stir around her, but was dumbfounded when almost immediately she'd turned back to eating—flicking her tail against the spot in her buttock where the dart had struck.

It was Kilian's 532nd successful vaccination since she began darting four years ago—and the first of several she did that day. For Sullivan, her first dart of the day delivered her 374th vaccination. Since forming its agreement with the NDA in April, AWHC's volunteers have delivered more than 1,100 vaccines. They estimate that amounts to about 50 percent of the Virginia Range mares. Their goal is 65 percent for the year.

As I prepared to leave that day, the property owner stopped me and thanked me for covering the horses. “We love them,” she said.