Fertility Management 

Image captured by a JMHA trail camera.

                  ​Due to economic stress and other factors, finding quality adoptive homes for captured mustangs is increasingly difficult.  Therefore, controlling the population of mustangs while keeping them in the wild is vital to their survival as an American icon. Fertility regulation is the most powerful tool we can use in this effort.  
               Early in 2024 JMHA gained an agreement with the forest service that allows for darting with a contraceptive vaccine called porcine zona pellucida, or PZP.     

The Challenges of PZP 

            After working for several years to place mustangs in the best adoptive homes we could find, the members of JMHA have come to be of the opinion that keeping the mustangs in the wild is in the best interests of the wild horses. The use of PZP (porcine zona pellucida) fertility control will help us achieve this goal. Herd management through the use of contraceptives has been around for some time; the use of PZP has been the most extensively studied method,(more information) and has proven to be an effective means of regulating mustang populations without the use of gathering. Yet, because of some of the challenges presented by PZP, the Forest Service and Bureau of Land Management have been slow to fully implement the use of PZP in regulating the herds under their care.  Below are some of the challenges that have hindered the governmental agencies' use of this humane option.

Timing

          While it poses no threat to an unborn foal, PZP is most effective in mares that are not in foal, or have never been pregnant.
Although a mare who has been dosed with PZP when she is in foal is less likely to conceive again, between pregnancies is the optimum time to administer PZP.  A mare can become pregnant again just one week after giving birth leaving a very narrow time frame to find her on the range and inject her for peak efficacy.
​ For this reason, knowing the correct time to inject a mare is important.   Keeping records of each mare and her pregnancies is the best way of maximizing the performance of PZP in the wild horses.

Boosters

​           Because PZP is an immunocontraceptive, or vaccine(more information) with a 95%-97% efficacy.  It  causes a mare's immune system to create antibodies that make her infertile for a time. For best results, a booster shot should be given between 3 and 6 weeks after the initial injection.  After approximately 10 months her antibody titers will begin to fall, and the mares must be re-injected. This pattern can be repeated safely for up to 4 years without serious risk of permanent infertility.
Again, accurate mare identification and record keeping are important factors in administering PZP.

Administering PZP

        A wild mare must either be trapped and restrained or darted to inject her with PZP.  Trapping  has the advantage that it is easier to keep track of the injections, but it is costly and stressful, with high potential for injury. 
    Darting is the easier option, but keeping record of which mares have received injections is a much bigger task. The range of the darting device is about 30 yards. The wildness of  the herds makes it difficult to even get within range of darting. Often, the horses will move off before accurate record of the mares can be made, let alone an attempt to dart one.  The noise of the darting device spooks the horses, with repeated exposure, mustangs learn steer clear of the darters.

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         Despite all of the challenges, JMHA is excited to be moving ahead with a fertility control program in the Jicarilla herds. Early in the spring of 2024, trained darters working for JMHA and the forest service began darting and documenting their data into government-developed software to create accurate records of the fertility control program.  The first few months of the program saw 34 mares darted. During the fall of 2024, darting parties will renew their efforts to dart more horses and administer some mares with booster doses. Additionally, JMHA is maintaining a spreadsheet designed to make tracking and identifying mares that need to be darted or boosted easier in the coming years. 
       Our first efforts in this program proved to be very enlightening. The steep learning curve we experienced will guide the methods we use for darting in the future. Each band of wild horses has its own distinct character and behaviors influenced by the most dominant mare and stallion.  As we gain understanding of each band, we can tailor our approach to darting so that we are able to get within range of darting without spooking the horses. Opportunities to dart multiple horse in a day are rare, as the darting devices make a loud noise causing the band to flee once an attempt to dart a single horse has been made.  The need for patience and strategic planning are crucial in our wild horse management efforts. JMHA remains committed to forming strategies to control herd growth rates with the goal of stopping or reducing the gathers.

 Studying the Herds

Image captured by a JMHA's trail camera.

         Along with keeping records of band movements, behavior, and member horses, JMHA has also DNA tested select horses that have been captured. To date, the horses tested have shown Mangalara Marchador, Galiceno, and Garrano DNA, all of which are breeds descended from the Iberian peninsula from horses brought to the Americas by conquistadors.  Establishing that the Jicarilla horses carry ancient Spanish blood in their veins, validates their worthiness of protection as living artifacts of history.

 
     Since 2021 JMHA has used trail cameras to capture band pictures and GPS locations to develop a database for identifying individual horses. The information gleaned from the cameras has been instrumental in understanding the daily behavior of the bands. We have learned where the horses get water, their travel paths, and areas where the bands graze or congregate.  This intel gives our darters the best chances to dart the maximum number of mares in the least amount of time, but darting mares one animal at a time is still a complex and time consuming process.

Image captured by a JMHA field study camera.

JMHA's Future Goals 

               While JMHA's  PZP program is huge stride forward in long-term maintenance of the Jicarilla herds, gathering and adoptions are still ongoing.  Regardless of best intentions and efforts, some mustangs do not adjust well to captivity.  It is the dream of JMHA's members to one day have a sanctuary to house and retrain mustangs that have experienced failed adoptions, or special needs horses that are less adoptable.  At this point, the purchase of property for a mustang sanctuary seems like an impossible dream, but three short years ago, having a PZP program felt like an unattainable dream. With the right support, anything is possible and we will continue with our aims for the future.

Image captured by a JMHA trail camera.

You can help JMHA

 preserve our wild horses.

Our efforts to study the herd requires the use of a considerable amount of equipment and resources. 
 Also, until roundups and trapping can be abandoned in our area, we will  continue to assist in finding excellent homes for the horses gathered.  JMHA covers many of the expenses involved in training and caring for the mustangs we are trying to home. Your monetary gifts go entirely to helping horses!

Keep our mustangs wild!

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