Wild horses in western Colorado are entering the second year of a fertility program designed to decrease birth rates among the herds so less animals will have to be removed for adoption.
Curr-ently, only the Little Bookcliffs herd, near Grand Junction, is undergoing the experimental treatment but successful results could lead to an expansion to other wild herds in western Colorado, according to Linda Coates-Markle, the Montana-Dakotas wild horse and burro state lead with the Bureau of Land Management.
"Our goal is to develop the fertility control vaccine to a level where we're completely assured it's safe and effective for broadscale use," Coates-Markle said.
The program works by darting wild mares with a vaccine that prevents them for becoming pregnant. Available vaccines can prevent a mare from becoming pregnant for one or two years. Researchers currently are working on a 3-year vaccine as well, Coates-Markle said.
The BLM maintains 206 managed herd areas in 10 western states, including four herds in western Colorado with about 800 horses. It is responsible to maintain the herds within specific management areas. And it removes animals annually to maintain herd sizes and prevent them from overwhelming the vegetation in a given area.
Wild horse herd populations increase at a rate of 10 to 15 percent per year, Coates-Markle said.
"If we let it go unchecked, it would have a serious detrimental effect on the forage base," Coates-Markle said. "Population control by the BLM is absolutely necessary."
The BLM's tool for controlling the populations is to round up horses and put them up for adoption. But Coates-Markle said of the 10,000 to 15,000 horses removed from the wild, only 5,000 to 8,000 are being adopted annually. Housing the animals yet to be adopted is expensive and in the early 1990s, the BLM began investigating other tools for managing herd sizes.
The long-term project requires extensive research of the herds to identify the mares and determine which ones to vaccinate. It includes one year of pre-application research to establish a "baseline" by which to measure the horses' normal social structure, mating habits and reproduction. Several years of vaccinations then take place, followed by two years of post-application studies of the BLM's findings.
Coates-Markle said the vaccines have been tested extensively even before their introduction into western herds, proving that when the vaccination runs its course, the mares return to fertility and produce a healthy foal.
"We just want to document that this is the case in western herds," Coates-Markle said.
According to Coates-Markle, the horses continue to breed normally, even when the vaccine prevents them from becoming pregnant. The vaccine only causes a mare's body to produce antibodies around the covering of viable eggs, which prevents fertilization.
Jeremy Browning can be reached at 824-7031 or firstname.lastname@example.org.