"I think the high price of energy, the economy, the price of hay is having a huge impact on our program. People across America now need to make a choice: Do I buy another horse or buy gas for my pickup?" Bisson said.

Caring for so many animals is crippling the agency's budget, the deputy director said.

Last year about $22 million of the entire horse program's $39 million budget was spent on holding horses in agency pens. Next year the costs are projected to grow to $26 million with an overall budget that is being trimmed to $37 million, Bisson said.

Continuing current practices would require a budget of $58 million next year, escalating to $77 million in 2012, BLM estimated.

"We have a responsibility to balance the budget, so we are going to have to make some tough choices," Bisson said. "We don't want to do this at the last minute. So we need to have a conversation with horse advocates and try to share the pain a little bit so people understand that if we have to make those tough changes it's not because we want to."

Bisson said none of the alternatives will be popular.

"I want to be really clear," he said at the board meeting June 30. "We have not made a decision as to what we're going to do at this point."

If roundups are ended, he expects an outcry from sheep and cattle ranchers who see the mustangs as competition for feed on the open range. If horses are euthanized, the outrage will come from horse protection groups, he said.

"Those are difficult choices to make," Bisson said. "But the law allows us to utilize those choices or some combination of that."

At least three roundups are planned in the coming weeks to remove about 1,700 wild horses in Nevada, where the BLM says ongoing drought has left dwindling forage and water for an overabundance of animals.

Bisson said the board will have to make the difficult decisions when it meets in September.

Jill Buckley of the American Society for the Prevention of Cruelty to Animals said she was concerned with another option that would allow outright unlimited sales of horses, as opposed to adoptions where owners are screened and pledge to keep the animals for a year.

While slaughtering horses is banned in the United States, Buckley fears many would be taken to Mexico or Canada where it is legal.

"We don't want to see that happen," she said.

Neda DeMayo, founder of Return to Freedom, a wild horse sanctuary in Lompoc, Calif., also questioned who would determine which animals are left on the range and which are removed

"So far, there been no conservation oversight," she said, to ensure "genetically healthy viable herd structures."