An American land management programme is planning to capture 575 wild horses this month and administer contraceptives in order to control population growth.
The 650-strong Cedar Mountain herd in Utah is growing by 20-25% each year, but scientists say the area can only support 400 horses.
Of the captured 575, 80 mares will be injected with a contraceptive and returned to the area with 50 stallions. The remainder will be put up for adoption.
Although birth control has been administered to mustangs in the past, this operation will be the most extensive use of contraceptives to date.
Supervisors hope it will lead to fewer wild horses being captured for adoption, euthanased or dying through lack of forage.
The federal protection of mustangs falls under the 1971 Wild Free-Roaming Horses and Burros Act.
“By law, we have to manage this herd so there aren’t large die-offs,” programme director Gus Warr told The Salt Lake Tribune.
Madeleine Pickins, wife of billionaire T Boone Pickins, has revealed that she will adopt most of the horses if she can find enough land to support them. The horses will be up for adoption from 21 February.