The petite brown mustang with the crippled leg was on a mission to get back to his makeshift family — two blind mares.

As dozens of wild horses were rounded up at their 680-acre South Dakota home and herded into metal trailers in mid-February, the yearling refused to get on the trailer and repeatedly jumped the fence to reach his companions, who were frantically spinning in circles.

"He just didn't want to leave them," said Nancy Turner, executive director of This Old Horse, a nonprofit Hastings horse sanctuary that agreed to take the two mares and their friend. "They needed to stay together."

The trio's friendship, rescuers said, demonstrates horses' strong emotional connections and resiliency, having survived life at a troubled ranch and the threat of being sent to the slaughterhouse or euthanized.

"They have their own culture," Turner said. "They trust each other — we're like Martians to them."

Nineteen horses — 10 of them blind — have arrived in Hastings since October as part of a massive rescue operation involving 900 wild horses. The horses had been at a rescue facility run by the International Society for the Protection of Mustangs and Burros in Lantry, S.D., for 17 years. They were impounded after an employee and whistleblower reported that they were neglected and starving after overgrazing destroyed their food source.

In the fall, Elaine Nash, who was called in by the state to coordinate the horses' adoptions, found homes for 270 of them with animal rescue operations and private homes across the country. The future of the others remained uncertain.

They were in danger of being auctioned off to pay their hay bill until Nash — with the help of major animal welfare organizations like the Humane Society and the ASPCA — raised $150,000 to keep them from possibly being sold to a slaughterhouse.

The rescue effort wraps up Sunday when the 300 remaining horses are expected to be transported to Colorado for eventual adoption.

"This is the largest number of horses rescued in the history of the country … that anyone knows about," said Nash, executive director of Fleet of Angels, a Colorado based nonprofit that transports horses in trouble.

Divvying up the horses, whose roots in large, wild herds extend back centuries, is "absolutely heart-wrenching," Nash said. "But we don't have a choice."

This Old Horse, started in 2012, already had about 40 retired and rescued horses at a facility called Wishbone Ranch. About 70 more horses are housed at various locations through a foster program.

The nonprofit has 1.5 full-time equivalent workers, but relies on 1,300 volunteers and $300,000 a year in donations to care for the horses. Taking on more didn't really make sense, Turner said, but Nash was persuasive.

The inseparable threesome arrived in mid-February, after Nash convinced Turner to adopt a few more horses.

The small male horse is Owen, even though his nickname was Jumper when he arrived, Turner said. His back left leg was likely damaged at his old home and healed incorrectly.

One of the blind mares is 30-year-old domestic with bay markings called Gypsy, while the other is named Hallie, short for Hallelujah. Hallie, chestnut in color, is about 10 years old and descends from a wild herd native to Virginia.

Many of the horses from the South Dakota sanctuary are blind, probably because of a contaminated water supply, Turner said.

The horses weren't used to being touched when they first came, but are becoming more accustomed to humans.

"They're not aggressive," Turner said. "They're like deer, but they're scared."

The three are usually kept together in either the barn or an outdoor pen. They "were like glue" in the beginning, Turner said.

"[Owen] protected them and gave them a sense of boundaries," she said. "He settled them into the barn. They would spin … and he was their senses."

The three make daily progress, Turner said, and they gradually are spending more time apart.

Five days a week, volunteer Lacrisha Elliott works with Owen, either alone or with the mares.

Elliot found herself drawn to Owen and decided that she wanted to be the one to help him and his mares feel safe. Owen now lets her pet him on his neck, face and stomach, though his legs are off limits.

Owen is a curious, quick learner who still protects the mares, Elliot said.

"They're always going to have that bond," she said. "There's nothing that's going to be able to break that."