It faced a legal challenge and announced this week it had abandoned the castration plan.
On Friday, its Rock Springs Field Office released its new plans for the herd areas, which involved removing excess wild horses to get them down to appropriate management levels.
It intends to gather about 90 per cent (or about 873 wild horses), removing roughly 696 excess wild horses. It plans to leave 205 wild horses in the White Mountain area and 69 wild horses in the Little Colorado area.
All mares released back to the areas would be treated with the Porcine Zona Pellucida (PZP) vaccine.
Sex ratios would also be adjusted, favoring stallions to mares.
The gather, it said, would reduce the current population of nearly 1000 wild horses in the two herd areas, which would be roughly three times the appropriate management level.
The appropriate management level for White Mountain is 205-300 horses, and for Little Colorado is 69-100.
The last gather involving the two herds was in November 2007.
The gather operation is scheduled to begin within the next 30 days, and is expected to last about three weeks.
All gathered mustangs will be examined by a veterinarian, dewormed, Coggins tested, and given booster shots. The wild horses will then be available for adoption to qualified applicants.