by Anthony Marr
When Charles Darwin first revealed his theory of evolution, his friend Thomas Huxley exclaimed, “It is so simple and obvious! Why didn’t I think of it?!”
It is because Huxley, like most people, thought inside the box, meaning within the confines of an established concept, while Darwin not only thought outside the box, but left the old box behind before sailing around the world on the HMS Beagle.
A similar principle applies to resolving the difficulties in managing wild horse and burro contraception to keep the population within the carrying capacity of habitat administrated by the Bureau of Land Management.
This is the only habitat where wild horses and burros are protected, even to a limited extent, by the 1971 Wild Free-Roaming Horses & Burros Act, which prohibited the slaughter of wild horses and burros, and further charged the BLM with the responsibility of protecting them for life..
Wild horses and burros are not tolerated on land managed by the National Park Service. Though wild horses and burros are tolerated to a limited extent on other public lands, only the Bureau of Land Management has a specific mandate to protect whatever population is deemed compatible with the other Congressionally mandated uses of the property, chiefly grazing livestock and energy extraction.
Inside-the-box thinking is to send personnel and equipment out on the range to dart and re-dart selected mares with immunocontraceptives, or capture them for conventional injection. Both approaches are very expensive.
Much easier alternative solution
Outside-the-box thinking produces a much easier alternative solution.
In Management Options for a Sustainable Wild Horse & Burro Program, an April 2018 report to Congress, the Bureau of Land Management (BLM) admits to a more or less stalled state of progress on immunocontraceptive research, development and implementation.
This results primarily from the BLM not presently having the means to deliver immunocontraceptives, a certified technology for both horse and deer, to a large enough number of mares to make a big enough difference in herd sizes on the open range.
The chief difficulty in using the single-year immunocontraceptive Zonastat-H is that the mares first must be field-darted. Then, a month or so later, the same mares must be redarted with booster shots, especially hard to do if the herd is highly mobile in a large territory with rugged terrain.
Currently, use of Zonastat-H is limited to small herds with relatively restricted habitat.
To use the two-year immunocontraceptive PZP-22, each mare must be captured, immunized by injection, held for a month, re-injected with the booster shot, then set free. The expense to hold thousands of mares for a month each is prohibitive.
Effectively using the one-shot, multi-year time release capsule SpayVac requires rounding up thousands of mares for injection––who are then set free.
Effectively administering the immunocontraceptive GonaCon poses the same delivery issues.
Cost of care
All in all, the BLM’s effort to achieve zero population growth among wild horses still on the range falls dismally short.
The Bureau of Land Management is further handicapped by the cost of caring for the 50,000 horses who have been removed from the range with respect to the land’s carrying capacity for the horse, who now must be kept for the duration of their lives if not adopted out, as stipulated in the 1971 Wild Free-Roaming Horses and Burros Act.
To cut costs, Congress has ordered the Bureau of Land Management to abide by a 2016 amendment to the Act, which allows the BLM to sell and/or “euthanize” any number of the captive horses “without limit,” as the BLM sees fit.
45,000 “unadoptables” may go to slaughter
Considering that only about 7% of the 50,000 horses in captivity are likely to be adopted, based on the 47-year history of the Bureau of Land Management wild horse adoption program under a variety of administrations, 93% of the 50,000 horses, or about 45,000 “unadoptables” in all, may go to slaughter.
Supposedly this would increase the budget available for research and development, and implementation of other wild horse herd reduction strategies.
But if the proposed sale of wild horses to slaughter proceeds, it may disable a workable outside-the-box solution before it has a chance to be implemented.
Wild horses do have natural predators, including wolves, pumas, and grizzly bears, but because these predators are discouraged from occupying BLM-managed grazing land, especially wolves, predation pressure is insufficient to suppress wild horse population growth.
Therefore the total wild horse herd on BLM property increases by about 20% per annum.
How to immunize 3,000 mares per year?
Theoretically then, immunizing about 20% of the on-range mares, or roughly 3,000 per year, should suffice. But the old inside-the-box solutions simply could not keep up.
The fastest, most effective way to do this is not to go out to the open range to immunize 3,000 mares. Instead, mares can be immunized among those––30,000 or more––already in captivity.
What about the booster shot? Waiting the month for the booster shot, if needed, incurs no extra expense, since these mares would be held as captive-horses-for-life in any case, if not sent to slaughter.
Once the necessary injections are done, the immunized mares would be returned to the wild, whether or not back to the respective herds from which they were captured.
(Since mares frequently move from one stallion’s harem to another, moving from one specific habitat to another is a normal part of a wild mare’s life.)
Maintaining the appropriate management level
This would avert all of the difficulties inherent in on-the-range darting and redarting, and the need to round up horses for injection.
This approach would, however, increase the number of horses on the BLM-managed range by the 3,000 immunized mares returned to the wild, raising the on-range population to 30,000, instead of the 27,000 that the BLM deems the appropriate management level.
I would suggest leaving the on-range population at 30,000, with supplemental feeding for the non-reproducing extra 3,000 mares as needed to protect the habitat. Again, this would require no extra expense, since these mares would need to be fed anyway, be they in captivity or at liberty.
The advantage of infertile mares on the range
The advantage of leaving the 3,000 infertile mares on the range is that if stallions are spending much of their time capturing and guarding harems of mares, of whom 20% to 30% are infertile, then herd fecundity will be reduced.
The reduction will be achieved even more rapidly if we take the option of removing 3,000 unsterilized mares from the range at the same time the treated mares are released, though if this option were selected, not mine, the method of removal must be humane and stress-free, and out-of-the-box thinking has also created solutions in this department.
All in all, this makes for a far more efficient and effective method of contraceptive delivery, which can prevent horse slaughter once and for all.
ANIMALS 24-7 responds:
Anthony Marr, a lifelong horse person and animal advocate whose name actually means “horse” in Chinese, is offering a wild horse population control technique which is not only accessible and workable, but also has a very long-established correlative in the Sterile Insect Technique, used for more than 60 years to control and even eradicate diseases transmitted by mosquitos, fruit flies, and screwworms.
Despite the obvious differences between wild horses and the insect hosts and carriers of deadly zoonotic diseases, the central problem is the same: how to rapidly reduce the populations of animals who are numerous, highly fecund, and broadly distributed.
Saturating the area where the numbers must be controlled with sterile males is the usual Sterile Insect Technique approach, for reasons specific to the reproductive behavior of insects, but saturating herd management areas with sterile mares would be more appropriate to the reproductive behavior of wild horses.
As Marr points out, this could easily be done by returning mares who have already been sterilized to the range. Our understanding is that a substantial number of mares currently in BLM holding pens have been sterilized in previous immunocontraceptive tests. These could provide a “starter” population for tests of the equine version of the Sterile Insect Technique that might get underway tomorrow, with the will and initiative to do it.