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Wildlife

Fertility control used on West’s wild horses

Written by Christy Hemken
    According to the Bureau of Land Management’s Wyoming Wild Horse and Burro Specialist Alan Shepherd, every manager of wild horses in the U.S. is looking at fertility control to slow the 20 percent reproduction rate.
    Currently the BLM uses a contraceptive program in mares that lasts anywhere from 22 to 24 months after treatment and utilizes porcine zona pellucida (PZP). The treatment consists of a liquid dose and the implantation of three time-released pellets that keep boosting the mare’s system and building up antibodies to prevent her from conceiving.
    The treatment costs around $225 per mare, not including the cost of capture. “If the treatment works, and the mare’s system doesn’t fight it, it can prevent one, two or even three foals from being born, which saves thousands in capture, feeding and adoption fees,” says Shepherd. “If we have to put a horse into long-term holding it can cost $10,000 to $15,000 over its lifespan, if not more.”
    Out of 70 mares recently treated in Utah, Shepherd estimates the agency can prevent 135 foals from being born. “That will save hundreds of thousands for the program in the future,” he says.
    Ongoing research seeks to find a longer-lasting treatment, which Shepherd says would make it more acceptable in some states. The Humane Society of the United States (HSUS) is looking at how mares respond after treatment and the impacts of not conceiving each year.
    “The Humane Society is a big proponent of the fertility control, and they hold the permit from the FDA that allows us to use the treatment,” says Shepherd. Because the treatment is still experimental the FDA requires somebody to hold its permit before it can be used.
    This year there will be treatments in Nevada, Oregon, Colorado and Utah as well as Wyoming if winter gathers are possible.  
    Shepherd says that treating any number over 50 percent of the mares captured will start to make a dent. In recent Utah treatments 70 out of an estimated 100 mares were treated, and he says that percentage should show some benefits.
    Endocrinologist and member of the Wild Horse and Burro Advisory Board Vern Dooley of Powell says the difficulty with wild horses in the West is that they’re never all gathered, making close management impossible. “The real issue is you have to gather enough mares to make the treatment effective,” he says.
    “Our goal is to have 70 percent of the mares on the range treated with PZP,” says Heidi Hopkins-Fedrizzi, HSUS Wild Horse Program manager.
    Although Shepherd thinks the fertility control is a useful tool, he says it’s not going to ever eliminate gathers in general. “You can’t catch all the mares and treat them all, and it doesn’t work on all mares, but it works and it’s been shown that it works.”
    Of other fertility treatments, Dooley says the BLM is considering any and all options. Of gelding wild horses, he says, “Most vets will tell you gelding a horse is not band-aid type surgery. When you’ve got wild horses that are a little harder to manage and geld you’re certainly going to want to observe them for a few days. It’s a much more complicated procedure than simply giving a shot.”
    Dooley says there has been some work done on bloodless castration procedures and sterilizing male mammals through various methods. “There really isn’t anything available at this point outside of doing a vasectomy or a castration,” he notes. “Those are difficult procedures to accomplish out in the field.”
    BLM has given some consideration to maintaining herds composed entirely of geldings. “They’re considering every possible notion we could do to minimize us having to deal with the horses and having to harass them in any manner and at the same time not do damage to the resources, which is BLM’s first objective,” says Dooley.
    “There are some people that think it only natural to let the horses go ahead and starve to death, but the problem is that before they start starving to death they’ve hammered that grassland and that has long-term implications on the resource,” says Dooley. “BLM will try to manage in such a way that we don’t destroy the grassland.”
    Currently, 33,000 horses reside on BLM ranges in 10 Western states. Another 30,000 reside in long-term holding facilities at a cost of 74 percent of the agency’s $37 million budget.
    Christy Hemken is assistant editor of the Wyoming Livestock Roundup and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..