Pickens, wife of Texas oil tycoon T. Boone Pickens, proposes using a million acres of the United States western rangelands for the rehoming and management of the 30,000 wild horses and burros currently held in captivity by authorities.
There are now as many horses held by federal authorities in holding facilities as roam the rangelands in the land-locked states.
The bureau says it is grateful to Pickens for her interest in helping to deal with the challenges of managing wild horses and burros, both on and off Western public rangelands.
However, the bureau has to date raised two issues it has identified as problems with the plan. The first centred on her plan to graze the horses on land where wild horses did not exist before the passing, in 1971, of the Wild Free-Roaming Horses and Burros Act. The latest centres on funding.
The bureau said that last November, Pickens offered to take over the care of thousands of wild horses held in facilities across the United States by setting up a private foundation that would care for the animals at no cost to the government, potentially saving taxpayers millions of dollars.
"Mrs Pickens' more recent proposal seeks a bureau stipend of $US500 per horse, per year for the life of each horse," the bureau said in a statement.
"Under this plan, Mrs Pickens' foundation would first take about 10,000 wild horses currently in BLM short-term holding facilities (corrals), the costs of which are significantly greater to the BLM than those of keeping horses in long-term holding (pastures).
"To realise these potential savings to the BLM, however, Mrs. Pickens' sanctuary plan would need to meet certain requirements for wild horse management.
"First, Mrs Pickens' plan to care for these animals at $US500 per horse, per year is similar to the long-term holding contracts that the BLM currently has with private landowners in the Midwest, where about 22,000 unadopted or unsold animals are cared for at an annual cost of about $US475 per horse.
"The animals graze on private pastures in Oklahoma, Kansas, and South Dakota, where forage and water are abundant. In contrast to these annual contracts, Mrs. Pickens has asked the BLM to commit to lifetime payments. Because Congress appropriates the agency's funding on an annual basis, the BLM is not authorised to make such an unlimited commitment."
"Second, Mrs Pickens' plan proposes to take the animals from private pastures and facilities and instead graze them on private and public lands on a large ranch in Nevada. However, current Federal law prohibits the BLM from using allotments associated with that ranch for grazing wild horses.
"The Wild Free-Roaming Horses and Burros Act restricts animals to the areas where they were found roaming when the Act was passed in 1971. Unfortunately, none of the BLM grazing allotments that Mrs Pickens proposes for her sanctuary were areas where wild horses roamed in 1971.
"Congress would have to amend the Wild Free-Roaming Horses and Burros Act to address this aspect of Mrs Pickens' proposal," the bureau says.
As an alternative, the bureau has offered to advertise a holding contract on private land and welcomes a bid from Mrs Pickens' foundation. "Open bidding on such a contract would ensure that taxpayers get the maximum benefit from their investment."
The bureau says it is committed to working with Congress, stakeholders, and the public to ensure the welfare of wild horses and burros, both on and off public rangelands, while also protecting these Western lands from the destructive effects of herd overpopulation.
"The BLM is committed to continuing its discussions with Mrs Pickens to address these challenges, which include the effective management of wild horses and burros and the protection of taxpayer dollars expended through the BLM's Wild Horse and Burro Program."