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A onetime free-roaming Utah stallion, whose picture sparked an Internet campaign demanding his release, died last week of a heart attack at a BLM holding corral in Delta as a veterinarian was gelding him.

The 26-year-old black-and-gray horse — officially known as Grulla stallion 3970, less officially known as "Antonino" — was to be sent to a South Dakota ranch where wild horses run free.

It was supposed to be a happy ending to the controversy surrounding the stud's removal from the West Desert range along with 102 horses last February. Instead, the stallion died July 28 during a gelding procedure.

"He lost his freedom, his family. Then, his two best friends were adopted and taken away a few weeks ago," wrote advocate Jacquelyn Hieber, who bought the horse and others, in a posting on the American Wild Horse Preservation Campaign's website.

"If you ask me, he died of a broken heart," Hieber wrote. "With his freedom and family gone, he didn't know a better day was coming."

That better day was meant to come at the 11,000-acre Black Hills Wild Horse Sanctuary at Hot Springs, S.D., to which Hieber had entrusted the horse. Founded in 1988 by Oregon rancher Dayton Hyde, the ranch is home to 600 mustangs. Hieber's goal was to reunite the horse with at least 10 others she bought from the same Utah herd.

Now, as word of Antonino's death spreads, wild-horse advocates have started pointing fingers, questioning why the old stud was being stripped of his manhood and who ordered the procedure.

Castration is risky for older horses, but Hieber and Black Hills sanctuary managers wanted the horse neutered, according to Lisa Reid, a spokeswoman for the Bureau of Land Management.

"He was an Internet sensation. The last thing we needed was for him to die," Reid said. "We were excited. He was going to go to a good home. It upset the guys."

Karla Larive, a spokeswoman for the Black Hills sanctuary, did not respond to an email.

When the stallion's photo appeared on BLM's Internet Adoption Program website in April, he captured the public's imagination. Someone assigned a Spanish name, evoking the stud's Old World lineage.

Horses from Utah's Sulfur Springs herd have distinctive markings and are more easily adopted that most wild horses pulled from Western rangelands, according to Reid.

The horse's pedigree likely traces back three or four centuries, when Spanish explorers' escaped horses began populating Western ranges and established bands of wild horses that roam free to this day.

Today, the animals are federally protected, and their proliferating numbers are causing conflict with cattle grazers and Western states because free-roaming horses compete with cows for forage. Millard and Beaver counties are ground zero in the battle because of the growing Sulfur Springs herd, now numbering three to four times the 200 horses BLM deems appropriate. The horses have roamed out of their designated "herd management area" and congregate near State Route 21 south of Garrison, posing a traffic hazard.

Under pressure from the state, BLM rounded up 103 horses and agreed not to return any to the range. Three died after the roundup — one died while foaling, and another was euthanized because it had lost its teeth — and the others were trucked to holding corrals in Delta.

But BLM's subsequent adoption efforts were a success. Of the 83 animals put out to bid in the first round, which excluded mares with foals, 63 were sold. The highest bid for Antonino came in at $1,760 from Brenda Grigg of Cascadia Horse Park in Montesano, Wash.

But Hieber's petition to put Antonino back on the range and the social media frenzy convinced Grigg to pull out of the deal.

"We had chosen not to geld this beautiful stallion when we won the bid. But as political pressures mounted from other organizations and people who demanded he go to a sanctuary, we retracted our bid and are still awaiting a refund from the BLM," Cascadia posted in a statement on its Facebook page. "Rest in peace, beautiful stallion. And for your kind, we hope the rest of the mustang community will stop fighting amongst themselves and realize their vision of how things should be are not always right."

BLM went down the bidder list to find another taker. The next-highest bidder declined. The third-highest bidder, Black Hills sanctuary, at $1,200, agreed to take Antonio as long as he was gelded, according to Reid.

To minimize the risk associated with anesthesia, BLM's contract veterinarian opted to administer Antonino a dose designed for a smaller horse, which proved insufficient, Reid said. After the vet began cutting him, Antonio kicked and went into cardiac arrest.

"They performed CPR," Reid said. "They had just started the procedure."

She emphasized that BLM did not require the procedure, although the American Wild Horse Preservation Campaign insists gelding is BLM's standard procedure for studs taken off the range.

Reid said studs generally are required to be gelded before adoption, but the BLM had made an exception for horses from the Sulfur Springs herd because of their breeding value.

"Now the heat is on, and they are trying to kick it back on the BLM."