POWELL, Wyo .
A Bureau of Land Management official says birth control is an effective way to control wild horse populations, but won't eliminate the need for periodic roundups. In 2004, about 500 horses in the McCullough Peaks outside Powel l were rounded up. Ab o u t 1 0 0 h o r s e s we r e returned to their range, including 36 mares that were given a birth-control drug. Alan Shepherd, a BLM wild horse specialist in Cheyenne, said the drug lasts one to three years and has proven at least 80 percent effective. He said the method slows growth of wild horse populations from 20 percent a year before vaccination to around 10 percent a year. The birth control drug porcine zona pellucida, or PZB costs $200 per mare. Shepherd said rounding up, feeding and transporting a mustang from the McCullough Peaks costs around $600. Shepherd said if another roundup occurs in the next year or so, about 100 of the McCullough Peaks' 185 horses would be returned to their range. Of those, 30 to 35 mares would receive PZB shots. The other 85 horses would be adopted out. "We still have horses to put into good homes," Shepherd said. Marshall Dominick, president of Friends Of A Legacy, a group dedicating itself to McCullough Peaks wild horses, said he's not totally sold on PZB. But he said if the drug proves safe, it could help avoid the need for horse roundups. He also said the drug could save the BLM money by controlling horse numbers. "I think we need to proceed with caution," Dominick said. "That is the key." The drug also has been used on ponies on Assateague Island, Md., for more than 15 years. Dominick said the drug has stabilized the island's pony populat ion and the National Park Service, which oversees the ponies, hasn't had to remove any young animals from the island.