Drought Forces Bureau of Land Management to Limit Births

The Bureau of Land Management (BLM) has proposed the use of a non-hormonal contraceptive--porcine zona pellucida (PZP)--over the next five years to limit equine overpopulation of the Pryor Mountain Wild Horse Range. BLM officials say the range has been taxed by drought conditions and growing herds.

In an Associated Press (AP) article, Linda Coates-Markle, BLM's wild horse and burro specialist, said the BLM plans to administer the contraceptive to 11 mares until the year 2010 along with removing 24 of the more than 160 wild horses on the land (located in southern Montana and northern Wyoming) to lessen the herd's impact until a long-term solution can be made. The program could be suspended for a year if the herds have lower-than-average population increases.

"We have to limit grazing impacts, at least temporarily, until we get out of the drought," she said in the article.

The agent porcine zona pellucida is an intramuscular immunocontraceptive that uses the immune system rather than hormones to prevent egg fertilization. It is derived from pig zona pellucida, a strong membrane that forms around an ovum as it develops in the ovary. Porcine zona pellucida causes the mare's immune system to make antibodies that bind to the mare's zona pellucida and prevent sperm from penetrating the membrane. Treated mares continue to cycle and ovulate normally, but they cannot conceive. The drug will not affect mares already in foal.

A study conducted in a BLM wild herd in 2000 showed that PZP was 90% effective in preventing equine pregnancies.

Comments on the project were to be accepted until May 5.

Dave Pauli of the Humane Society of the United States, which partnered with the BLM on the project, told the AP, "Long-term, we would rather have a safe, healthy herd than an overpopulated, stressed herd."

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for TheHorse.com .

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