Stallions may undergo chemical vasectomies to keep herds in check

The mares having done their share, stallions might someday be the target of pilot birth-control efforts in a northwest Colorado wild horse herd.

“It’s basically what we consider a chemical vasectomy,” Wendy Reynolds, manager of the BLM’s Little Snake Field Office in Craig, explained last week during a meeting of the BLM’s Resource Advisory Council for northwest Colorado.

The procedure involves capturing and anesthetizing stallions and giving them injections that take effect within about three days, she said.

She said she plans to meet with state-level BLM officials about possibly trying out the approach on the Sand Wash Basin herd west of Craig as an alternative means for limiting wild horse numbers.

“We’re looking to find some better solutions to deal with this,” she said.

The BLM already has been treating mares by darting them with PZP, a vaccine that delays fertility.

The agency is struggling with burgeoning populations of wild horses in Colorado and other states. It’s buffeted between interests such as ranchers who worry about the toll the horses take on rangelands and wild horse groups that oppose rounding up and removing horses to thin their numbers.

The BLM’s goal is to keep the Sand Wash herd between about 160 and 360 horses, but it’s now at 406, not counting the 60 or 70 foals expected to join the herd this spring. The population is projected to reach 700 by 2016.

“We’re not going to adopt those out. That’s not going to happen,” Reynolds said.

She said people don’t want to adopt because of the price of hay these days. And there’s not enough room at holding facilities for wild horses to add a couple hundred more, she added.

Jim Cagney, the BLM’s district manager for northwest Colorado, said the BLM’s entire budget for wild horse management is literally being consumed by feeding horses that already have been captured.

Last year, with the help of volunteers, the BLM successfully darted more than 90 mares with PZP. But Reynolds said that process is quite difficult, as it requires darting the same female at two different times, which means having to be able to identify individual mares. Sometimes the treatment still doesn’t work, and regardless, the PZP eventually wears off and treated mares become highly fertile, which makes it important to repeat the process.

She said chemical vasectomy has been shown to work in managing animals such as deer and elk, and for horses on private property. And unlike castrating a stallion to make it a gelding, which can result in a less aggressive horse afraid of fighting studs, a horse that receives a chemical vasectomy continues to act like a stud and also will help protect a herd, she said.

Like other herds, the Sand Wash population has lots of public supporters. The herd even has its own Facebook page with 18,000 followers, with some individual horses having their own pages, Reynolds said.

“For us it’s a very delicate dance to finesse any type of population reduction, but we know we have to do it,” she said.


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