Agency Sage Grouse Review Puts Thumb on Scale to Magnify Wild Horse and Burro Effects
The method used by the U.S. Bureau of Land Management to assess range conditions is seriously skewed toward minimizing impacts from domestic livestock and magnifying those from wild horses and burros, according to an appraisal by Public Employees for Environmental Responsibility (PEER). As a result, the BLM’s approach to range management targets scattered wild horses and burros while ignoring far more numerous cattle. The agency’s assessment is part of a 2013 report on factors influencing conservation of the Greater Sage-Grouse, a ground-dwelling bird whose numbers have declined as much as 90% across the West and which is under consideration for protection under the Endangered Species Act. That report concludes that twice the area of sage grouse habitat is negatively impacted by wild horses and burros than the area negatively impacted by livestock. A PEER appraisal of the methodology found:
“At BLM apparently not all hooves are created equal,” said PEER’s Advocacy Director Kirsten Stade, noting that the LHS evaluations cover more than 20,000 grazing allotments and examine whether a grazing allotment meets the agency’s standards for rangeland health with respect to several vegetation and habitat conditions. “This helps explain why wild horses are regularly removed from the range but livestock numbers are rarely reduced.”
The BLM assessment influences not only the agency’s range management decisions but also will figure into the Fish and Wildlife Service’s decision on whether to list the sage grouse under the Endangered Species Act.
Last year in response to a complaint by PEER filed under agency Scientific Integrity policy, BLM claimed that it does not have enough “reliable data” about commercial livestock impacts to include them in current assessments of environmental conditions on Western range lands. Yet, BLM has more data on the grazing that it authorizes through permits than virtually every other topic.
“When it comes to cattle, BLM plays with a marked deck,” Stade added, pointing out the PEER analysis that will become part of PEER’s new grazing reform web center set to launch in several weeks. “We are posting BLM’s own data in a way that allows apples-to-apples comparisons while displaying satellite imagery that depicts the true livestock landscape impacts.”
Compare BLM claims to what their data reveal
The relative negative influence area of feral ungulates with respect to domestic livestock based on BLM’s spatial analysis approach (USGS OFR 2013-1098) are completely at odds with BLM’s own land health standards (LHS) evaluation causal data, used to inform BLM’s analysis. BLM concludes in OFR 2013-1098 that the negative area of influence of feral ungulates is twice that of domestic livestock, when the records show that only 3% of grazing-related failures of standards are attributed to wild horses and burros.
Largely unchecked by natural predators, many wild horse populations grow at rates of 18–25 percent per year. This unregulated growth can overtax vegetation and affect herd health as well as native wildlife populations. The Wild Free-Roaming Horses and Burros Act of 1971 requires the U.S. Bureau of Land Management (BLM) and USDA Forest Service to manage these free-roaming herds for a “thriving natural ecological balance.”
To ensure the sustainability and health of both horse herds and the public lands they roam, and to reduce the number of animals requiring either adoption or long-term care in holding areas, managers began to explore fertility control as an alternative management technique.
From 1978 into the 1980s, the BLM worked through a series of research contracts focusing primarily on development of a chemosterilant for wild stallions. In the early 1990s, research turned to silicone implants in mares in an effort to achieve fertility control. Although both routes produced fertility control, they had too many drawbacks and were eventually abandoned.
In light of these problems and the continuing need for some form of contraception, in 1991 researchers identified the desired characteristics for an ideal wild horse fertility control agent.
Specifically, the agent should:
How PZP works
In order for sperm to attach to the ovum and fertilize the egg, there must be complementary proteins on both the surface of the sperm and the zona pellucida (ZP) of the ovum. PZP acts as a foreign protein against which the treated mare produces antibodies (thus, the PZP fertility control agent is actually a vaccine). These antibodies attach to the mare’s zonae sperm receptors on the ovum and block fertilization. Domestic pig ovaries (obtained from slaughterhouses) are minced and the PZP is obtained from screening filtration. An adjuvant is mixed with the PZP to enhance its effectiveness when it is injected into mares intramuscularly. Once injected, it causes an immune response, making the mare infertile. Over time, the antibody titers fall and fertility returns. With the liquid vaccine, a booster injection can be given at 10 months to raise the titers back to the infertile range. This can be done each year for at least 4 years, after which time the effects may be more likely to become permanent. For this reason, current individual-level field trials involve only 1–4 years of treatment.
This list of needs would drive much of the U.S. research on wild horse contraception during the 1990s, including research funded by both the BLM and the U.S. Geological Survey (USGS). To meet the stated criteria, a National Park Service research team on Assateague Island National Seashore turned to an immunocontraceptive agent, porcine zona pellucida (PZP), which had been reported to block fertilization in dogs, rabbits, and primates. Experimental PZP application on the wild horses of Assateague Island commenced in 1988, resulting in promising reductions in the pregnancy rates of mares: by 1994, population growth began to stabilize solely through the use of PZP immunocontraception.
The Outlook for PZP
The PZP agent appears to meet most of the safety concerns of the BLM. The fact that PZP is a glycoprotein suggests that it should be digested before it can enter the food chain. Its effects passively wear off with time if annual injections are terminated; normal reproduction can be resumed following at least 4 years of use, and perhaps more. It does no harm if injected into mares that are already pregnant—they carry foals to term. Initial research suggests that PZP does not affect ovarian function or hormonal health. Life span seems to increase with improved health of treated mares, apparently due to the absence of stresses from pregnancy and lactation. Treated mares can live 5–10 years longer than untreated mares that continue to get pregnant and produce young. An initial study suggested that harem behaviors are not influenced, and more in-depth investigations are currently underway. There appear to be no generational effects; offspring of treated mares are able to reproduce normally. Finally, at least some forms of PZP may be 90% effective in blocking fertility in mares (see Wild Horse Resources, Fertility Control in Mares).
PZP has been successfully applied to control fertility in several small populations of wild horses on eastern barrier islands since the early 1990s. Population-level field trials of an injectable, time-release, pellet form of PZP that will allow almost 2 years of fertility control with a single treatment are currently underway in many western herds. The Assateague team also developed noninvasive methods to assess the pregnancy rates of, and detect ovulation in, free-ranging treated and nontreated, individually recognizable mares by analyzing reproductive steroid metabolites in their feces and urine.
PZP Field TrialsThe USGS, BLM, and USDA Animal and Plant Health Inspection Service (APHIS) have essentially completed individual-level field trials of PZP in free-roaming wild horses at three locations: Pryor Mountain Wild Horse Range, Montana and Wyoming; McCullough Peaks Herd Management Area, Wyoming; and Little Book Cliffs Wild Horse Range, Colorado. Application of PZP began in 2001 at Pryor Mountain, in 2002 at Little Book Cliffs, and in 2004 at McCullough Peaks. Results of this work in terms of horse behavior are reported in Ransom et al. (2010), and efficacy results are detailed in Ransom et al. (2011). In addition, in 2011 the USGS, BLM, and the Animal and Plant Health Inspection Service (APHIS; Department of Agriculture) began studies on the safety and efficacy of SpayVac®, a form of PZP made using a proprietary technology developed by Immunovaccine Inc. (Halifax, Nova Scotia, Canada).
Source: USGS, Fort Collins Science Center
MONTH / yEAR