BLM Tests Fertility Drug to Control Wild Herd Growth

The Bureau of Land Management (BLM) has begun testing a new fertility-control vaccine it hopes will become an alternative to contraceptive porcine zona pellucida (PZP) for controlling wild herd growth. While some wild horse advocates believe the vaccine could reduce the need for controversial wild horse gathers, others maintain that the agency is not allowing enough public scrutiny of the testing.

In use by the BLM since the 1990s, PZP is injected into wild mares to produce antibodies that prevent sperm from attaching to an egg and fertilizing it. Mares on the range receive PZP via dart gun, while gathered mares are administered by syringe. The contraceptive is effective for about a year.

Earlier this month, the BLM began testing oocyte growth factor (OGF) on 16 previously gathered wild mares in Nevada as part of a joint research project with the USDA/Animal and Plant Health Inspection Service’s (APHIS) National Wildlife Research Center.

Said Tom Lenz, DVM, MS, Dipl. ACT, member of the BLM’s National Wild Horse and Burro Advisory Board, OGF prevents wild mares’ oocytes from maturing, rendering the mares infertile. Once administered, the vaccine is effective for at least three years. It can also cause early menopause in mares.

“Eventually it would be permanent for vaccinated mares,” Lenz said, adding that he appreciates its long-term potential. “It could reduce or even eliminate the need for gathers,” he said.

Despite that potential, Laura Leigh of Wild Horse Education questions the safety of the mustang mares used in the study.

“BLM is conducting experiments without public oversight,” she said. “The public could not assess the condition of mares prior to application, nor can the public independently monitor any detrimental effects of the new substance—it’s simply not okay.”

Research into OGF use in just getting underway, but Lenz said the study’s results could affect more than the welfare of wild herds.

“I hope it works,” he said. “This is not just a wild horse issue, it’s a complete environmental issue.”