VETERINARIANS IN THE WILD

Resident (in green) instructs students how to anesthetize and monitor a wild stallion

Veterinary team helps at Wild Horse Sanctuary -- students gain experience in surgery, anesthesia, animal handling and wildlife issues.

The first challenge in examining a wild stallion is getting him into the chute. That's what a team of 33 veterinarians, staff and students found on Friday, February 15, 2002, when they trekked 150 miles from Davis to Shingletown's Wild Horse Sanctuary. Tucked into the forest near Mt. Lassen National Park, the non-profit refuge is the 5,000-acre home to hundreds of feral horses, remnants of domestic breeds abandoned or lost generations ago by Spanish horsemen and Western settlers.

It also happens to be the site where equine reproduction specialist Irwin Liu periodically "rounds up" a student-veterinarian crew to donate veterinary services. In exchange, he and his colleagues turn the experience into practical lessons for senior students in wildlife handling, anesthesia, surgery, and ecosystem management.

Dr. Irwin Liu

While Liu observed the herd and consulted with sanctuary co-founder Dianne Nelson about the day's strategy, team members set up a temporary pharmacy, unpacked surgical instruments, and laid out equipment, including portable X-ray and anesthesia machines.

Health screenings, handling

Though smaller in stature than many breeds, wild horses show formidable strength while being corralled and handled, as the crew learned early by drawing blood samples from a group of mares. Staff and students all lent a hand in restraining and calming each mare so students could reach in to take a sample before she returned to her companions in an adjacent paddock.

Other tasks included sedating and gelding stallions and performing health checks on members new to the herd. Most animals were to be adopted, but a few from each round-up remain at the sanctuary.

Crew prepares animal for surgery

In all, 25 animals were examined. Faculty and veterinary residents took charge of each patient's anesthesia, surgery-and student instruction. Students monitored vital signs of anesthetized animals and learned to gauge factors such as age, size, and temperament. In efficiently organized teams, students learned the steps in castration and other procedures, including a tendon surgery, X-raying of unshod hooves for instructional purposes, and an abdominal operation conducted by faculty surgeons. Staff members charted data, and all shared in moving sleeping animals to the recovery area.

The last of the 19 sterilized patients was gently awakened near sunset while Liu consulted again with Nelson about follow-up care-and the team's next visit. As clouds lifted and darkness fell, students packed the vans and left the hills, taking with them new skills and greater understanding of wild horses and their singular needs.

Faculty members conduct surgery and supervise teams

Population control of feral horses

Advocates press for the preservation of the wild horse, but the animals compete with each other, cattle, and other wildlife for scarce food and water on public lands. To reduce stress on the environment, government agencies round up the horses regularly for adoption or relocation. The School of Veterinary Medicine assists the sanctuary with routine sterilizations, a humane way to prevent overpopulation of the horses where their range is limited.

Irwin Liu has conducted equine fertility studies with this unusual herd in collaboration with Dianne Nelson. His interest in feral horses and their impact on ecosystems led to the development of an experimental form of birth control for mares known as immunocontraception. The product acts as a vaccine, stimulating antibodies in the female that prevent fertilization of her eggs. The porcine zona pellucida vaccine (PZP) is 95% effective in preventing pregnancy for up to two years. Liu has used the vaccine on Tule elk and bears in regions where their populations must be managed.

After a single round-up in 1999, Liu gave PZP injections to roughly 800 mares, dramatically reducing the number of foals that year from the normally expected 400 to only 40. Other experimental successes have been equally dramatic. One advantage of this birth control method, he explains, is that it does not disrupt the animals' natural behavior, so the horses maintain the social herd structure essential for their survival in the wild. Dianne Nelson adds that at the Wild Horse Sanctuary, when females have 1-2 years of rest between pregnancies, they enjoy better overall health.

With an estimated Western population of about 40,000 feral horses-about half live in Nevada-a long-term, humane form of equine birth control could trim expenses of the government's management program, reduce environmental stress, and protect horses remaining on wild lands.

---

School of Veterinary Medicine photos copyright 2002 by Regents of the University of California. Written permission required for reproduction of these images.