Equine advocates have been scrutinising the bureau's horse population counts for several years and assert the numbers don't add up.
"The bureau doesn't make it easy to track horses being removed from the range or residing in short and long term holding," alliance representatives John Holland and Vicki Tobin said in a statement.
"The taxpayers who pay for the removals and the subsequent care are not allowed to view the horses under the well-worn excuse that they are being held on 'private property'. Consequently, there are no checks and balances to verify information being reported.
"It also raises a salient question. With 262 million mostly vacant acres under its control, why on earth is a federal agency such as the bureau wasting taxpayer's money to lease private property?"
The alliance said the bureau was increasingly using the "private property" wild card "whenever they don't want the public to see what they are doing" - whether during actual horse removals or subsequent holding.
The alliance, an umbrella group with more 115 member organisaitons, said there are either 2282 horses missing from the bureau's wild horse holding facilities or the agency's numbers are not accurate.
As of July 9, 2010, the bureau has removed 5334 horses from public lands and yet, an increase of only 625 horses is reflected on their most recent population facility chart for fiscal-year 2010.
"A first grade child could do the math by taking the number of horses reported on holding facility charts, adding the number of horses rounded-up and subtracting the number reported as adopted and sold and quickly discover the totals are not accurate," Holland and Tobin noted.
The bureau numbers do not even reflect the 300 to 500 adopted horses the bureau says are returned by adopters each year, or the number of foals born in captivity.
According to a 2008 Government Accountabily Office (GAO) report, 303 foals were born in long-term holding during fiscal-year 2007.
In either case, adding those numbers to the counts only increases the number of missing horses.
After allowing for the deaths, the bureau should still have 36,073 horses in holding facilities but they are reporting only 33,791 on the June 2010 holding facility chart.
"Where are the 2282 horses that are missing from BLM's accounting of the horses in holding facilities?" asked alliance vice-president Valerie James-Patton.
The GAO report said the bureau was not required to report the number of deaths in long-term holding facilities.
The alliance questioned whether 2282 horses could have died in captivity in just a nine-month period.
"How can we have any confidence in the bureau's estimates of the wild horse population when they can't even count the number of horses in their pens?" asked alliance president John Holland.