PZP: Where hope, science and mustangs meet


The longtime mustang advocate, TJ Holmes, and I head into southwestern Colorado’s Spring Creek Basin Herd Management Area, searching for mustangs. We do this regularly. TJ has documented these mustangs for eight years, working in partnership with the Bureau of Land Management. A big part of her work is administering PZP, the fertility-control vaccine (porcine zona pellucida), to the mares.

The air is heavy and smoke-filled from recent fires. Topping a rise, we see mustangs silhouetted against the hazy gray sky: three bands, each comprised of a stallion, his mares and grown offspring; and a group of young bachelor stallions. TJ recognizes each horse on sight and knows the roles each plays within the herd. I’m learning, and I see that something is missing — foals, the fillies and colts of springtime. 

Spring Creek Basin has a BLM-allotted carrying capacity of 35 to 65 adult horses, and is at about 60 right now. Yet there could be 20 foals on the ground, and there are only two, one before us napping with his mama in the heat, the second far across the range. More could come this year, but even with the expected three to five foals, this herd management area will not reach maximum capacity. 

That means no wild horses will be removed in 2016 or 2017, and no mustangs will head toward the overcrowded, short-term holding facility at East Cañon Correctional Complex near Cañon City. 

The last BLM roundup in Spring Creek Basin took place in 2011, when 82 mustangs resided in this herd management area, including 13 surviving foals (eight had died). The agency removed 40 horses, and for the next four years, TJ darted mares with PZP. Trained by Dr. Jay Kirkpatrick, senior scientist at the Science and Conservation Center in Billings, Montana, TJ used PZP on 10 mares the first two years, which dropped foal numbers to eight in 2013, and seven in 2014. The BLM then permitted TJ to dart more than 20 mares, and what we see before us — just one colt nuzzling his dozing dam — is the result of her successful PZP program.    

Wild horse in Wyoming, where PZP is also being tested.

PZP does not harm mare, fetus or nursing foal in any way, though a mare might buck or jump from the sting of a dart in her rump. Mares are not vaccinated every year; a BLM selection process based on genetics, age and herd health indicates which horses get the dart. PZP, which is reversible, causes eggs to reject sperm, though mares continue to cycle normally, with no disruption to herd dynamics or psychology. Stop the darting, and the mare can conceive again.

Still, some folks oppose PZP, seeing it as human meddling. But let’s face it: We’ve already meddled — digging ponds in desert soils to catch water, erecting fences to prevent mustangs from accessing natural water sources used for generations, ending “free roaming.” Solutions presented by the public are opposing and dramatic: Reinstate slaughter practices, or do nothing at all. Both are equally terminal ideas: death in the slaughterhouse, or death by starvation.

Introducing PZP into a herd area is the wisest action BLM can take for horses, habitat and the American public. With fewer horses born, fewer roundups happen, more years pass before removal is necessary, and fewer horses are taken to holding facilities. All this saves taxpayer dollars, and for the horses, fewer are traumatized and die unnecessary deaths. 

Taxpayers pay about $49,000 for each mustang removed from the range and not adopted. PZP costs about $27 per darted horse per year, and often the darters are volunteers like TJ, who works for mustangs, not wages. PZP has effectively slowed herd reproduction in Spring Creek Basin, as it has in Colorado’s Little Book Cliffs and Sand Wash Basin, and in additional herd management areas across the West. 

“The McCullough Peaks area in Wyoming reached zero-population growth in just three years,” Dr. Kirkpatrick told me, adding that the potential taxpayer savings was $7 million. “The Challis (Idaho) Herd Management Area is just getting started and estimates they have already saved more than $350,000.” Why, then, is the BLM not using PZP in every herd management area? That is the question the public needs to ask the BLM.

Horses, reintroduced to the Americas in 1493, are here, just like the rest of us. They have reoccupied this land for 500 years. We don’t have the wherewithal to control human population, homelessness and hunger, but with a $27 injection, we could make a huge difference in life on the range.

Kathryn Wilder is a contributor to Writers on the Range, the opinion service of High Country News. She has mustangs and cows and lives in Dolores and Disappointment Valley, Colorado.

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