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Bureau signals ongoing use of PZP on wild horses

November 26, 2010

by Laurie Dixon

Eleven wild-horse musters in the United States this fiscal year will take place with the primary aim of giving mares a long-term contraceptive, the Bureau of Land Management says.

A vaccine for fertility-control will be given to mares gathered from the western rangelands in the US. © BLM
The bureau, which is charged with caring for the estimated 38,000 wild horses in the western rangelands, says the 11 musters will take place during the 2011 financial year.

It says it will apply the fertility-control vaccine known as PZP to about 890 mares in total during the "catch, treat, and release," musters.

The mares will be released back to the herd management areas from which they were gathered.

While some animal advocacy groups back the use of a long-term contraceptive, including the Humane Society of the United States, others do not believe it is an acceptable solution, arguing that it plays havoc with the social order within herds.

However, bureau director Bob Abbey describes it as "an innovative way of working to control the population growth of wild horse herds".

"If these fertility-control treatments prove successful, we can lengthen the time between some gathers, saving taxpayer dollars by holding down gather and holding costs."

Porcine Zona Pellucida, or PZP, which makes mares temporarily infertile, is not available for commercial use.

The bureau uses the vaccine in co-operation with the Humane Society of the United States under Food and Drug Administration rules that apply to research on new animal drugs.

This vaccine was first tested on the wild horses of Assateague Island, off the coasts of Maryland and Virginia, where a reduction in mare pregnancy rates was observed.

The bureau says wild horses and burros have virtually no natural predators and their herd sizes can double about every four years. As a result, the BLM must remove thousands of animals from the range each year to control herd sizes.

It says there are currently 12,000 more wild horses roaming the rangelands than the appropriate management level, which is set at 26,600.

Off the range, there are 37,800 other wild horses and burros that are fed and cared for at short-term corrals and long-term pastures. (As of October 2010, there were about 11,400 in corrals and 26,400 in Midwestern pastures.)

All wild horses and burros in holding, like those roaming the public rangelands, are protected by the BLM under the 1971 Wild Horse and Burro Act.

Major wild horse advocacy groups wants a moratorium on wild horse gathers pending development of a new management plan.



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