A bipartisan group from Arizona’s U.S. House of Representatives delegation is calling on the U.S. Forest Service (USFS) to establish a plan to manage the growth of the Salt River feral horse herd.

Since 1971, Congress has federally protected wild horses and burros and placed them under Bureau of Land Management jurisdiction. However, feral horses such as the Salt River herd, derived from domestic horses that were turned out or escaped their owners, are not covered by the federal law. Earlier this year, the Arizona state legislature passed legislation protecting the horses and placing them under Maricopa County Sheriff’s Office and USFS jurisdiction. The law also requires permission from the Maricopa County Sheriff’s Office or the Arizona Department of Agriculture (ADA) before anyone can interfere with the herd. The legislation will take effect once an agreement between the ADA and USFS is officially signed.

In a letter to U.S. Agriculture Secretary Tom Vilsak, six Arizona house members called for Salt River mares to be immediately treated with porcine zona pellucida (PZP, an immunocontraceptive vaccine) to manage herd growth.

The groups sent the letter after the USFS denied a plan that would have allowed the Salt River Wild Horse Management Group (SRWHMG) and its national partner, the American Wild Horse Preservation Campaign, to proceed with a plan to vaccinate the mares. Simone Netherlands, SRWHMG president, said the plan was rejected on grounds that USFS is not authorized to manage the herd and, therefore, cannot authorize others to conduct herd management practices