A Bureau of Land Management helicopter swoops in to herd horses in Great Divide Basin, Nevada.
(image 1 of 8)Wild mustangs from the White Sands herd in New Mexico, now living on the South Dakota range.
(image 3 of 8)T.J. Holmes on the range in Disappointment Valley in southwestern Colorado, where she uses a rifle to shoot darts loaded with PZP, a substance that makes mares infertile for a year.
(image 4 of 8)T.J. Holmes takes aim at a wild mare on the range in Disappointment Valley in southwestern Colorado, using darts loaded with PZP, a substance that makes mares infertile for a year. She never misses.
(image 5 of 8)Jay Kirkpatrick has spent decades researching methods of birth control for wild horses. Now, he teaches advocates how to administer Porcine Zona Pellucida, or PZP, to wild horses on the range. Some local BLM offices are also using it.
(image 6 of 8)Vials of Porcine Zona Pellucida, or PZP, a birth control drug for wild horses.
(image 7 of 8)Horse carcass on the hillside of South Steens Wild Horse Management Area in southeastern Oregon.
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