Contraceptive darts control wild horse population in about half of Western management areas

Josie, a wild mare in Colorado, bore eight foals
in eight years, but over the past decade has been
shot with at least five darts (Photo submitted to E&E)

The wild horse population n the Western U.S. is being controlled one horse at a time through $25 contraceptive darts, but the hard part is tracking down the horses through vast, difficult ranges, Phil Taylor reports for Environment & Energy News. There are about 40,000 wild horses on public land in the West, and the Bureau of Land Management has corralled more than 100,000 in the past 10 years, placing about half in government-funded holding facilities.

Wild horse populations grow 20 percent annually, and experts say the only sustainable solution is an aggressive expansion of fertility control, Taylor writes. Holly Hazard, of the Humane Society of the United States, told Taylor, "We can't gather our way out of it. We can't adopt our way out of it."

"BLM officials are cautiously optimistic that the fertility control program can be expanded to more of the agency's 179 herd management areas, which cover nearly 27 million acres," Taylor writes. "Over the past decade, contraceptive darts have been used on 5,400 wild-horse mares in 87 herd management areas" in Colorado, Wyoming, Montana and Utah. Since 2002, when groups first "began darting the herd's mares, reproduction has dropped to more than a dozen foals per year -- less than 10 percent of the herd's 150 horses."

Mares "are darted with the drug porcine zona pellucida, a vaccine derived from pig eggs that changes the shape of receptors on mares' eggs, forcing them to reject sperm. It's about 95 percent effective over the first year," Taylor writes. "The drug, which is also used on elephants and wild deer, is widely supported by animal-rights advocates because it causes very few behavioral changes." (Read more)