Twenty-four mares have been targeted for fertility-control efforts over the next four years at the Pryor Mountain Wild Horse Range south of Billings.
The decision follows a finding of no significant impact issued by the Bureau of Land Management Thursday.
Birth control has been a contentious issue on the wild-horse range. Last year, two groups appealed the BLM fertility-control plan, temporarily halting implementation.
To curb the mares' reproductive capabilities, the BLM has been using porcine zona pellucida (PZP) vaccine. The contraceptive is delivered with dart guns. Opponents have argued, among other things, that the vaccine darts have caused large open sores on some mares. The BLM said lesions did occur in a small fraction of the horses to which PZP was applied in the past, but all healed without unusual scarring.
The BLM is also proposing to remove 11 bachelor stallions between the ages of 4 and 8 and 11 yearlings through capture. The stallions would be lured into corrals with bait, rather than by use of hazing or herding, which has been done in the past.
The agency wants to reach a target of 85 to 105 adult horses on the range, a herd size that has been criticized by some as too small to maintain genetic viability of the herd. Others argue that without herd reductions, the 38,000-acre range is doomed to be severely overgrazed.
Should the surviving foal crop drop too drastically, the contraceptive would be suspended for one year.
The Pryor herd consists of 138 horses (2 years and older) and 22 yearlings. The 160 horses include nine horses that have not been sighted this year. The herd is expected to produce up to 38 foals this year. So far, 24 foals have survived. The range holds the only free-ranging wild-horse herd in Montana.
The horses will be available for adoption once the 22 horses have been captured.
For more information on the BLM's record of decision, log on to www.mt.blm.gov/bifo/ whb/PMWHR/2006/index.html.