 Guss, the Stallion. Photo: ©Corolla Wild Horse Fund A young stallion named Gus just might be the key to saving the wild horses that roam the beaches of Corolla. The genetically-diverse wild stallion from Cedar Island, some 250 miles away, was released into the Corolla herd on Thursday. “He’s the offspring of some Shackelford horses who are the same breed as ours – Colonial Spanish Mustangs. They have far more maternal lines than we do. We are down to one maternal line. Our gene pool is very shallow. We are having birth defects, so Gus is historic,” explained Corolla Wild Horse Fund Executive Director Karen McCalpin. The process to get Gus into the herd has taken years and required approval from the U.S. Fish and Wildlife Service. Earlier this year, McCalpin pulled DNA samples by dart gun from two wild stallions living on Cedar Island. It was then analyzed by Dr. Gus Cothran of Texas A&M University who was able to confirm that the horses were Colonial Spanish Mustangs. The Corolla Wild Horse Fund decided to name the stallion Gus in Dr. Cothran’s honor. After Gus tested negative for Equine Infectious Anemia, staff from the CWHF made the trip to Cedar Island to transport Gus to the north beach in Corolla. The herd on Cedar Island has been owned and cared for by Woody and Nena Hancock. “Gus is the first step in turning that headed for extinction situation around. Without the introduction of new genes into the Corolla herd – they would cease to exist. We are already at a genetic bottleneck where we are having consistent birth defects in foals,” McCalpin told NewsChannel 3′s Todd Corillo on Monday. “Obviously we are hoping Gus finds some girlfriends and that offspring that he would produce would be the first genetically-diverse offspring here in centuries. We hope if not next year, the year after we’re going to see a foal that we know is the beginning of turning around the path to extinction for these horses,” she continued. As she watched Gus idly graze in his new Corolla home on an abnormally warm late-November day, McCalpin couldn’t help but be excited. “Seeing him is probably bigger than winning the lottery for me. People talk about a bucket list and that was certainly on my bucket list. It’s just amazing to me that we were able to do this.” McCalpin hopes to be able to return to Cedar Island in the spring to DNA test mares that could be released in Corolla as well. Source: WTKR by Todd Corillo The mission of The Corolla Wild Horse Fund is to protect, conserve, and responsibly manage the herd of wild Colonial Spanish Mustangs roaming freely on the northernmost North Carolina’s Currituck Outer Banks. The organization employs a darted immunocontraception program using the FDA approved substance PZP (porcine zona pelucida). It is conducted under the auspices of the Humane Society of the United States and the Science and Conservation Center in Billings, Montana.
If you would like to help the efforts to return the Corolla herd to genetic health, please donate. You can go to their website at www.corollawildhorses.org or by mail: CWHF P.O. Box 361 Corolla, NC 27927.  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 |
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