Sky Mountain Wild Horse Sanctuary

Carson National Forest PZP Management Project

Sky Mountain Wild PZP Project

Sky Mountain Wild and Wildlife Immunocontraception     

        We at Sky Mountain Wild Horse Sanctuary believe that the time is now for a different vision for wild horses. Since the1971 passage of the Wild Free-Roaming Horses and Burros Act, the primary means of “management” for wild horses in the U.S. has been roundup and removal of mustangs from their home range. Today in 2014, the Bureau of Land Management (BLM) has over 50,000 wild horses in holding facilities, mustangs that have forever lost their freedom through roundups. With an estimated 35,000 wild horses left roaming the western states on public lands, we now have more mustangs in holding than we have free in the wild.

       At Sky Mountain Wild, we realize our mission of engaging in humane, science-based action to keep mustangs free in the wild through a unique partnership with Mt. Taylor Mustangs and the Carson National Forest.  With our partners, we pioneered the first treatment of mustangs on Forest Service lands in the U.S. with the immunocontraceptive Porcine Zona Pellucida, or PZP. Treating mustangs with PZP means that wild horses remain free in the wild in numbers that are healthy for them and for the range on which they roam, as PZP safely limits reproduction. Sky Mountain Wild Horse Sanctuary funded the cost of treating the first Carson mustangs to receive PZP, and sanctuary co-founder Karen Herman and Mt. Taylor Mustangs owner Dan Elkins darted these wild horses with the PZP. Today, 73 mustangs in the Carson Forest Jicarilla and Jarita Mesa Wild Horse Territories have received PZP. These mustangs will keep their freedom, and the initial cost savings resulting from keeping them wild instead of rounding them up is conservatively calculated at $132,960.*  The additional savings resulting from limiting reproduction is $25,713 for foals that would have been rounded up and removed, for a total initial cost savings of $158, 674. This savings is for the initial costs of roundup and removal of wild horses, compliance, and preparing each mustang for adoption. It does not include the additional savings resulting from avoiding long-term holding costs for mustangs that would have been transferred to holding facilities to live out the rest of their lives.

        Today, Sky Mountain Wild continues to fund the Carson PZP Project and to help treat mustangs with PZP in the wild, while providing a life-long haven for the threatened mustangs we have adopted. We are engaging in strategic planning to keep all Carson mustangs free by using PZP to reach sustainable herd numbers, and to develop a model that can be used for wild horses throughout the west.

        The National Academy of Sciences 2013 Research Summary identifies immunocontraceptive as key for wild horses.

Sky Mountain Wild PZP Project

Porcine Zona Pellucida (PZP): What it Is, How it Works

        Treating wild horses with PZP to keep them free is a key aspect of Sky Mountain Wild’s vision of mustangs living free and thriving in wild places. PZP is an immunocontraceptive derived from pig ovum that vaccinates treated mares against conception. Dr. Jay Kirkpatrick of the Science & Conservation Center in Billings, Montana, pioneered the use of PZP for wild horses. Mares are treated using a jab stick or remote delivery with darts. Thereafter, mares may be treated once annually or every two years to maintain immunocontraceptive effects, and the vaccination is reversible up to seven years from treatment.

Twenty years of research demonstrates that PZP is:
  • 90 % efficacy

  • reversible

  • has capacity to be delivered remotely
  • safe for pregnant mares
  • safe for mares’ health with long-term use
  • maintains wild horse family bands and social behaviors
  • low cost
  • does not pass through the food chain

The Carson National Forest PZP Project: The Beginning

       On March 11, 2009, mares from the Carson National Forest Jicarilla Wild Horse Territory were treated with PZP. This marked the first time in the nation that PZP had been used for mustangs from a U.S. Forest Service Wild Horse Territory. Treating mustangs with PZP represents a vast shift in the management of wild horses in New Mexico, as previous management had been round-up and removal of wild horses from their territories. Those first mares to receive PZP were gathered and brought to short-term holding, where Dan Elkins and Karen Herman hand-injected them with the PZP. Miraculously, no arms were broken in the process, and the mustangs were released back into the wild.  Dan has since developed the means to dart mustangs out in the wild horse territories, which eliminates stress for them and keeps them where they belong.

Sky Mountain Wild PZP Project

Carson PZP Team:

Dan Elkins, Owner, Mt. Taylor Mustangs.

Dan is responsible for treating mares with PZP in the wild, and documenting and tracking treated mustangs and their family bands.


Karen Herman, President, Sky Mountain Wild Horse Sanctuary.

Karen is responsible for PZP protocol and database development and management, securing and managing project funding, and assisting with treating mares with PZP.


Anthony Madrid, District Ranger, Jicarilla Ranger District, Carson National Forest.

Anthony is responsible for ensuring compliance with U.S. Forest regulations and overseeing all project planning and management.

Photo Acknowledgement:

Claude Steelman

Sophia Marshall



Sherry Thompson, Executive Director, Thaw Charitable Trust – providing funding for the project.


Holly Hazzard, VP, US Humane Society – assisted with regulatory issues with FDA.

An article from the Santa Fe New Mexican on this project

*Cost savings is calculated using data provided by the Carson National Forest on the cost per mustang for roundup, removal, and compliance, which in 2011 was $2571 per wild horse. Cost savings for foals is calculated based on the $2571 cost per mustang with a 90% PZP efficacy and a 15% annual rate of reproduction.

copyright 2019 Sky Mountain Wild Horse Sanctuary