Managing Overpopulated Feral Horses in the Great Basin, USA

Emily Bartone, Natural Resource Conservation; Charlotte Sedgwick, Animal Science; Derek Tripp, Building Construction Technology

Feral, invasive horses crowd government-managed corrals

The Great Basin of the United States is currently inhabited by over 80,000 wild non-native horses. Being a wild non-native species, they survive without the assistance of humans in a region outside of their native distribution range. The horses we now see in the Great Basin were brought to this continent by Europeans during colonization. Historically, large predators such as mountain lions and wolves also roamed the landscape and could control these populations. Humans eradicated nearly all large predators during the past century of extensive development. This has left many prey species, including horses, free to expand without limit (Jackson, S., 2018).

Considering that humans are responsible for introducing horses and removing their natural predators, humans must face the challenge of managing this growing population. Many population control methods have been implemented, from birth control to adoption programs, that have not been successful at curbing population growth rates. It is time to take lethal means and open harvest of wild non-native horses to decrease population growth rates in the Great Basin.

Cattle ranchers in the region have felt the impact of wild horse grazing the most out of anyone. Mark Wintch, a rancher in Beaver County, Utah would marvel at the rare sight of wild horses when he was a young boy. Now, there are so many horses on the land that if he were to put his cows out there, they would starve (Philipps, D., 2014). In 2013, the Bureau of Land Management, or BLM, told Mr. Wintch and dozens of other ranchers that they should voluntarily cut their herd sizes in half because of the pressure horses put on the landscape. It is understood, however, that removing cattle will only increase the growth rate of the horse population. This would be a massive economic blow to the ranchers who depend on the health of the land for their livelihoods and pay for their cattle to use the land (Philipps, D., 2014). The grazing by wild horses has become such an issue for ranchers that Mr. Wintch and others have sued the federal government, demanding they decrease the number of horses by any means necessary. Those who oppose a lethal solution have a misunderstanding of the ecological and economic aspects of this issue. Ranchers in Mr. Wintch’s community face the brunt of the problems caused by wild horses and support them being slaughtered and the meat being put to some use (Philipps, D., 2014).

In 1971, congress directed the BLM and U.S. Forest Service to manage and protect the nation’s wild horses (BLM, 2018). Since then, the wild horse population on public lands has almost quadrupled (BLM, 2018). Unchecked herds double in size every four years. While up to an estimated 27,000 wild horses can live in balance with wildlife and livestock on healthy public lands, there are 82,000 wild horses living on public lands as of 2018 (BLM, 2018). A horse population of this size is absolutely decimating the Great Basin ecosystem. They graze at a rate which significantly decreases the health of native vegetation. A study in Nevada found notable and drastic differences in the structure, composition and character of the vegetation within areas with horse exclosures when compared to the vegetation outside of the exclosures (Beever et al., 2000). The species richness, or number of different species, was also significantly higher in the horse excluded plots, at between 24 and 25 total species, where horse grazed plots had between 5 and 10 total species (Beever et al., 2000). Boyd C.S. et al. (2017) found that the amount of bare ground is higher in areas where feral horses graze. In the areas observed, there was 60% less litter cover and an 80% decrease in herbaceous stubble height (Boyd CS et al., 2017). Another study found that in areas where horses have been removed, vegetation health improved significantly (Erik A. Beever et al., 2008).

Horses have a similarly disastrous impact on the fitness and survival of native wildlife species. Observing areas where horses monopolized water sources showed significantly decreased animal diversity and richness. Hall et al. (2016) calculated that horses were present up to 73% of the day, leaving very little time for other species to access the resources. Their primary competitors for resources are other large ungulates (hoofed mammals), like pronghorn and deer (Gooch et al. 2017). Much of this landscape is habitat for horses, native ungulates, birds and small mammals. These areas showed decreased animal diversity and species richness. For example, Beever et al. (2000) found 1-5 small animal burrows in the areas where the horses grazed and 15-22 burrows in the areas where the feral horses were excluded. This is because the horses disrupt the area to such a degree that other species cannot survive there. Horses trample the soil and brush that the small mammals rely on to build their burrows (Davies et al., 2014). It was also noted that horses defecated and urinated either in the water or very close by, effectively lowering the quality and cleanliness of the water for other animals (Hall et al., 2016). They are harming the health of the natural species both directly and indirectly.

In recent years, the government began attempting to remove horses from public lands by rounding them up and holding them in corrals on private ranches and feedlots. This process seemed like a success initially, but the financial burden of feeding and maintaining the horses is growing. The cost of holding horses in these corrals is $49 million annually (Philips, D., 2016, Norris, K. A., 2018). Over the life of these herds, the total cost is expected the reach $1 billion. The bulk of this cost is solely from feeding horses, meaning there is nearly zero funding remaining for other population management projects which could tackle the issue at the source: overpopulation (Philips, D., 2016). This process is not sustainable for either the landscape or the BLM funds. The corrals were intending to hold horses only until they could be adopted, but many never are, and end up dying in captivity. One rancher, who has had to dedicate much of his land to feral horses instead of livestock, called his range an “old folks home for horses” (Philips, D., 2016). Current management has run resources into the ground, and overpopulation of horses increases the likelihood of starvation and dehydration. Many horses are seen in poor health, showing signs of starving both in corrals and on public lands (Norris, K. A., 2018, Garrot, R.A., 2018). Because of the ecological damage the overpopulated horses have caused to the nearby farming communities and to the individual fitness of the horses themselves, the only solution that will result in significant change is to eliminate a percentage of the population through slaughter.

There is immense opposition to any plan that involves killing the horses or endangering them in any way. However, they are invasive species who are damaging the ecosystem and need to be thought of as such, not as pets or domesticated animals. The people who oppose slaughtering the horses have proposed many other solutions that have been considered and explored, but it has been concluded that they would not work for a population of this size. One popular proposed method of controlling the population of wild horses is birth control in the form of darts. The two most popular immunocontraceptive vaccines used on wild animal populations are Porcine Zona Pellucida, or PZP, and Gonacon (Hall et al., 2017, Samoylova et al., 2012, National Wildlife Research Center). PZP works by stimulating the immune system to produce antibodies that attack to the sperm receptors on the zona pellucida (the membrane that surrounds the egg), which blocks fertilization (Wildlife Fertility Control). Gonacon targets Gonadotropin-releasing hormone, or GnRH, which signals the body to produce sex hormones that control the functioning of the ovaries. The vaccine causes the body to make antibodies against GnRH, causing infertility (Miller et al., 2008). These vaccines have been found to be highly effective at preventing pregnancy, however they have yet to be implemented successfully with such a large population.

The most well known example of PZP being used on wild horses took place on Assateague Island (Masters, 2017). The population needed to be kept below 125 individuals to remain sustainable. This project has been running for 30 years now, which allowed the volunteers involved to grow familiar with the horses and for the horses to become comfortable with the presence of the volunteers. In order for this method to work, large numbers of dedicated volunteers are required. It is also necessary to have proper documentation of each horse’s vaccine history, habituated and approachable horses, and consistent, abundant funding. Kane explains that these conditions are next to impossible to achieve in the Great Basin. The vast majority of the horse population would need to be treated, and the treatment is no quick task. It consists of a primer dose, a booster dose four to six weeks later, and an annual booster each year after that (Masters). There is nowhere near enough manpower to accomplish this for a herd of this magnitude. It would also be extremely challenging and resource intensive to constantly inventory which individual horses have been treated. With this method, it would take many years to see a real change in the population and relieve some of the stress these horses are putting on the environment (Kane, 2018). In order to administer the annual booster, the horses would have to be frequently re-rounded up and held in corrals, time and time again suffering from lack of food and water resources. It is simply not feasible to implement this method as the primary solution to the ever-growing horse population crisis.

For similar reasons, a surgical sterilization program is not a an option for the wild horses of the Great Basin. Permanent methods of contraception may be most effective for limiting population growth, but this solution has many similar obstacles as the last. Surgical castration requires rounding up the animals, anesthetizing them, and performing surgery in the field, which are not ideal or sterile conditions (National Research Council). Post-operative complications from this procedure occur at a rate of 10%, yet post-operative care and management would be impractical and dangerous in the wild for both humans and horses (Ibrahim et al., 2016).  The expensive price tag of mass surgeries is another barrier to this method. Also, surgical castration performed at too young of an age results in a loss of male type behaviors. These behaviors are necessary for maintenance of social organization, band integrity, and expression of a natural behavior repertoire (Ibrahim et al., 2016). However, gelding (castrating) too old increases the risk of post-operative problems and requires more recovery time, which could be a death sentence for wild horses (Return to Freedom, 2018). Return to Freedom, a nonprofit dedicated to the protection of wild horses, points out that a mass sterilization of this magnitude has never been carried out and therefore the long term behavior and health of the herds cannot be predicted. Any plan that relies on sterilizing the majority of the horse population is not feasible, safe or practical, considering how large the population has grown.

The BLM has been adopting out contained horses for the past few decades, but adoption rates have never been able to keep up with population growth and therefore have not been a sustainable solution. In 2017, 2,900 horses were adopted out, a mere 3% of the total horse population of the region. Each year, more and more horses are brought into captivity in corrals with adoption being the goal. One source cited that from fiscal year 2012 to 2016, the BLM adopted and sold 13,597 animals but still added 7,830 animals to their holding facilities (Norris, K.A., 2018). Although it looks as if the number of horses being adopted annually is increasing, the population size is growing quickly. Because of this, the percentage of feral horses being adopted each year has actually been decreasing steadily (BLM, 2018). The BLM has imposed limitations on who can adopt horses because of pressure from animal advocacy groups concerned with horses being intentionally sold to slaughterhouses or meat processing plants (Garrot, R.A., 2018). There is no way to ensure the horses are going to homes where they will be well cared for, so they may end up suffering as much as they would if they stayed on rangelands and starved (Norris, K.A., 2018). The cost of adoption has also been a topic of debate. Lowering costs to increase accessibility has decreased the likelihood of horses going to adequate homes, but increasing the cost decreases the likelihood they will be adopted in the first place (source). The adoption program has not been able to keep up with the growing population, and overall has failed to reduce the number of feral horses in the Great Basin area. The program has only head to economic and environmental resource depletion, overcrowding and eventual starvation, and potential rehoming to inadequate caregivers.

A similar issue with wild horses damaging the ecosystem arose in Western Australia. A global review found that they were damaging waterways, degrading the soil, spreading weeds, altering the vegetation, and reducing the richness, abundance, and diversity of natural species (Nimmo, 2018). These horses were also introduced to the area, making them an invasive species. Their numbers have grown anywhere from 300,000 to one million (Marks, 2013). Experts considered many solutions, including fertility control through darts and adoptions, but came to the conclusion that the only viable solution was to directly cull (selective slaughtering) the population. There was immense opposition to the plan, but the research into the other methods showed it would not work on a population so large over such an immense area of land (Stanley, 2017). Animal welfare experts were also brought in to determine if the solution was ethical and they determined it was the most humane method of controlling the quickly expanding population. This is because the horses were dying from water deprivation or fighting over food sources (Stanley, 2017; Marks, 2013). Although this population is larger than the one in the United States, the conclusions about how to deal with this problem still apply. As the population in the Great Basin area continues to grow exponentially more issues will arise, so an immediate solution is needed and eliminating a part of the population is the only way to accomplish this.

Although it is the most controversial and most aggressive solution, hunting seems to be the most direct solution to the high population of wild horses while also creating revenue. Nevada law currently prohibits any unauthorized person from removing wild horses from public lands, harassing wild horses, or using aircraft or a motor vehicle to hunt wild horses (among other listed actions). Violation of this law is a misdemeanor and a person who willfully and maliciously kills a wild horse is guilty of a category C felony (Laws, 2011). This is very frustrating for farmers because they are constantly eating their livestocks food and drinking their limited water sources while the farmers have to sit back and watch it happen along with continuous growth of the horse population furthuring problems. Changing this law is the best solution to control the unsustainable growth rate of the wild horse population. Although there is a historically driven connection between U.S. culture and horses, there is no denying that they are already a threat to the ecosystem and the economy at their current population.

Population management plans such as this have been successful with other invasive species. In Alabama, it was previously illegal to hunt the invasive wild boar, also called feral hogs (Rainer, 2015). However, this species has a fast reproductive rate and no natural predators, just like the wild horses, and population sizes grew unchecked (Geisser et al. 2004) . They were destroying ecosystems and getting in conflicts with native species, which prompted the Alabama Wildlife and Freshwater Fisheries (WFF) Division to adjust its regulations on hunting the boar (Roney, 2018). This was an effort to empower landowners and lease holders in their battle against the wave of wild boar. Farmers pay a high price from the presence of wild boar in the form of damage done to row crops, pastures and farm roads, similar to farmers and ranchers living alongside wild horses (Amici et al. 2012). A 2009 study conducted by Auburn University concluded that wild boar in Alabama caused more than $74 million in damage (Emmons, 2017). To solve the problem, WFF and the Alabama Conservation Advisory Board approved a revision that would extend fur bearer status to the wild boar. This revision provided the legal method for trappers to legally trap and sell hog carcasses to meat processing plants which could inspect and sell the pork for consumption. Kevin Dodd, WFF’s Enforcement Chief, stated that people who trap hogs will be required to have a hunting license, if hunting commercially for someone else they will need a fur catcher’s (trapping) license to sell feral hog carcasses (Rainer, 2015). The current Alabama law allows the hunting of wild hogs after the purchase of a hunting license with no bag limit in all 67 counties. After a three year study of hog population in an area where hunting was legalized, it was found that hunting significantly reduced damages caused by wild boars (Geisser et al. 2004). A similar tactic could be used to control the horse population as well.

There are some restrictions to this being implemented for wild horses, but it is feasible. Although it would be a game animal meaning they are hunted for sport, hunters would be able to sell the carcasses, giving them incentive. Before 2007 when they shut down, three major equine slaughterhouses operated in the United States: Dallas Crown in Kaufman, Texas; Beltex Corporation in Fort Worth, Illinois; and Cavel International in DeKalb, Illinois. The slaughterhouses exported about $42 million in horse meat annually, with the majority going overseas. About 10 percent of their output was sold to domestic zoos to feed carnivores and 90 percent was shipped to Europe and Asia for human consumption. Although it is not illegal to process horse meat in the U.S., all meat must be inspected by a licensed inspector before selling. With these last few slaughterhouses having been shut down, it is impossible to process horse meat legally unless for personal consumption. Reopening a slaughterhouse in Nevada will give hunters a domestic location to sell carcasses by placing it locally to the source of horses and create a licensed meat processor to sell meat overseas. It would bring large amounts of money to the local economy post-export. Opening just one slaughterhouse would bring approximately $300 per horse and around $10 million annually to the U.S. on top of the profit made from selling hunting licenses (Whiting, 2007).

Although controlling the population of wild horses by hunting them is a very unpopular option among animal rights activists and horse lovers, it is the only feasible and immediate solution to this problem. Any other method cannot be executed on such a large population and will not be effective for the immediate future, meaning the horses will continue to damage the ecosystem and prevent ranchers from letting their animals out to graze. The ecosystem can not wait long enough for any form of fertility control to start taking effect. Even if a plan to sterilize the majority of the population was somehow executed there would only be an immediate decrease in birth rate, and the population size is what needs to decrease in order for the ecosystem to recover. Action must be taken immediately to prevent permanent and irreversible ecological harm to the Great Basin. In their current state, these wild horses are suffering from thirst and starvation because there aren’t enough resources available. It would be better for all components of the ecosystem if the population was at a sustainable level so with all organisms able to thrive. The only way for this to happen is to decrease the population size and growth rate by changing the laws that prevent horse slaughter in the United States.


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