BLM turns to birth control for managing wild horse herds

Nov 10, 2011

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The Bureau of Land Management is rounding up thousands of wild horses in Wyoming this fall, in an attempt to reduce herd sizes. Right now, there’s not enough forage on the range for both wild horses and livestock. So, as it has been doing for many years, the BLM is seeking to bring down the horse numbers. In previous years, the agency done that by removing horses from the range permanently. More recently, they’ve been adding another method: birth control. New numbers indicate that the drug is working, though it has its drawbacks. Wyoming Public Radio’s Willow Belden reports.

It’s a brisk fall day in the Red Desert. The sun has just come up … and officials from the B-L-M are preparing for the day’s roundup. They’ve set up a series of temporary fences to funnel wild horses into a trailer.

A couple of domestic horses are standing by. Their names are Shorty and Rooster, and they’re referred to as “Judas” horses because their job is to lead the wild horses into the trap.

Eventually, a helicopter comes into view. The pilot is chasing a herd of about 30 horses toward the trap site. When they get close, Shorty darts out from behind a snow fence and races into the trap. The wild horses follow blindly. Gates clang shut behind them. A calculated chaos ensues as horses scramble past each other.

Some of the horses are removed from the herd and put up for adoption. Others are given a fertility treatment called PZP, which is basically the equine version of birth control. The BLM is trying to reduce the wild horse population nationally from about 38,000 to roughly 26,000, and it’s been doing a pilot project here Wyoming to see whether fertility control is an effective way to accomplish that. It’s administered the drug every few years since 2006.

Scott Fluer administers the PZP and counts horses here in the Red Desert, and he says the drug is working.

FLUER: “What I found is reproduction is down – down around 10 to 15 percent. Normally in our wild horse management areas, reproduction is 20 to 25 percent.”

The numbers excite Fluer because the BLM is badly in need of a new method for managing wild horse herds. Until recently, the agency has kept populations down by removing horses from the herd. The problem is, it’s hard to find homes for older, un-trained horses.

FLUER: “We can offer up to 7,000 a year, but about half of that is getting adopted.”

Those that aren’t adopted are shipped off to the mid-west. Fluer says there are about 38,000 horses in long-term pastures there. And supporting them is expensive.

FLUER: “If we gather, say, a five-year-old horse and we send it to long-term pasturing, and that horse lives to 25, maybe 30 years of age, and you’re paying X amount of dollars per day to hold that, day after day, month after month, year after year, it does add up.”

It adds up to about $19 million a year total. The BLM is hoping to reduce that expense. Which means reducing the number of horses that go to sanctuaries. Which means curbing the number of foals that are born.

So how do you do that? One way is to tinker with sex ratios in the herds – in other words, remove more females than males. That hasn’t reduced birth rates enough though. More recently, the BLM considered castrating stallions. But environmentalists and horse advocates filed suit over that plan.  Suzanne Roy with the American Wild Horse Preservation Campaign says gelding stallions would catastrophically reduce the gene pool and upset herd dynamics.

ROY: “Stallions will exhibit great loyalty to their family bands, and they’ll literally fight to death to protect their mares and foals. And that sort of behavior would be destroyed by castration.”

Plus, researchers say castration wouldn’t reduce birth rates unless you fixed all the males, because whatever stallions were left would just inseminate all the females.

So the last remaining option is birth control. And most agree it’s a pretty good option. It does have to be administered every two years, but it’s still cheaper than keeping horses in long-term pastures.

And people like Roy say it’s the way to go.

ROY: “The fertility control is reversible. …  And as a non-hormonal agent, it has minimal impacts on their behavior.”

It’s not perfect though.

Dan Rubenstein is the chair of the Department of Ecology and Evolutionary Biology at Princeton University. He studied the effects of PZP on a group of horses in North Carolina, and he says mares on birth control tended to move around between herds more and continued to cycle later in the year than usual – all of which put stress on the horses.

But Rubenstein says those side effects shouldn’t be a deal breaker for PZP. He says overpopulation can also affect horses’ behavior negatively.

RUBENSTEIN: “There are definite consequences of PZP but there are also definite consequences of crowding on a landscape.”

Behavior aside, there’s still the question of effectiveness: Even if PZP cuts birth rates in half, is that enough to achieve target herd sizes? Scott Fluer with the BLM says no.

FLUER: “PZP alone, if we just catch, treat and release, won’t control the population in its entirety because we only gather 80 percent when we catch horses.”

That means 20 percent of the mares will still be having babies. But Fluer says that’s OK: he thinks birth control could reduce fertility rates enough that the BLM wouldn’t have to remove more horses than they can find homes for. And if that turns out to be the case over the next few years here in Wyoming, PZP could well become the centerpiece of the BLM’s wild horse management strategy nationwide.