Last week, when Karen Herman pushed a long metal tube to the hindquarter of a colorful mustang mare to inject birth control, the two made a little history.

The mare and three others in the Carson National Forest became the first wild horses injected with a contraceptive by the Forest Service as another method for controlling herd sizes.

It culminated months of hard work by Herman, a social scientist operating a wild horse sanctuary near Abiquiú; Dan Elkins, who is contracted to gather the horses; and Anthony Madrid, the wild horse and burro coordinator for the Carson National Forest.

The mares are among the estimated 400 wild horses that roam 76,000 acres of the Jicarilla Ranger District in northwestern New Mexico. The district needs to bring the numbers down to 100 to meet its management plan.

The herd is one of only three wild horse herds left in New Mexico out of eight herds that in 1974 totaled 6,000 mustangs. Less then 600 wild horses are left roaming free in the state now, according to agency estimations.

Herman hopes the birth control injections last week represent a shift in how the Forest Service manages the agency's wild horse herds. "It's time for different solutions rather than just round-up and removal," Herman said.

Ever since the Wild Horse and Burro Act began protecting mustangs in the 1970s, the ongoing problem is that horses keep having foals. The herd sizes grow too large to survive on land also shared with elk, deer and cattle. The Forest Service and the Bureau of Land Management, which has the largest herds, periodically round up the wild horses and burros and put them up for adoption.

But the agencies currently have thousands of horses in long-term holding facilities that remain unadopted and cost a lot of money to care for. And more wild horses are born every year.

Mustang advocates for years have pushed the use of well-monitored chemical contraception on the herds as a cheaper, more humane herd-control method than adoption. Patience O'Dowd, founder of the Wild Horse Observers Association, advocated using porcine zona pellucida, or PZP, several years ago on the Carson.

PZP was the birth control administered to the Jicarilla mustangs last week. Derived from pig ovum, PZP prevents sperm from fertilizing the mare's eggs. Developed and tested at the Science and Conservation Center in Billings, Mont., since 1987, PZP has been used for years by the National Park Service to control feral pony herds on Assateague Island. It also is used by zoos on some mammal species and has been tested on Eastern U.S. deer herds.

Herman and Elkins were certified by the Science and Conservation Center in Montana to mix and administer PZP to the horses. PZP is still considered an experimental drug by the FDA, so the Center manages all PZP requests. Data on all horses treated with PZP must be sent to the Center.

Herman said PZP has proven 90 percent effective in reducing pregnancy, can be used on pregnant mares without harming foals, and doesn't appear to change herd behavior. The effects last only about a year and are reversible.

The mares given PZP were among horses Elkins gathered last fall using nothing but hay for bait and an automatic gate on an enclosure. Elkins and Herman used a jab stick — a long metal cylinder — to administer the contraceptive. Horses can also be darted in the wild from afar. It cost about $1,000 a horse. Most of the money, time and equipment was donated by the PZP team. "The Forest Service didn't have money in their budget for it," Herman said.

The four paint mares given PZP last week were released back to their herd.

Mark Catron, district ranger for the Jicarilla Ranger District, said PZP will definitely be one of the tools his staff uses to manage the herd. But right now his focus is on reducing the size of the herd by gathering up horses and finding them homes. That's a tough go right now with a tanked economy and the expense of keeping a horse.

Diana Trujillo, district ranger for the El Rito Ranger District, said she's received permission from her boss at the Carson National Forest to also use PZP on the Jarita Mesa wild horse herd. "For us it makes a lot of sense. We are now within our management level, about 67 horses," Trujillo said. "We can use PZP selectively. That way we won't have to do as many adoptions."

The Thaw Charitable Trust has donated $25,000 to Herman's nonprofit Sky Mountain Wild Horse Sanctuary to continue the PZP effort. She hopes the team will be able to treat up to 50 horses in the next year.

For her, the bottom line is preserving mustangs in the wild, where they have survived for centuries.

Contact Staci Matlock at 986-3055 or smatlock@sfnewmexican.com.