While the Bureau of Land Management (BLM) is seeking ideas for managing its wild horse and burro population, some critics maintain that the agency has failed to appropriately implement previously suggested herd management methods.

The Wild Free-Roaming Horse and Burro Act of 1971 charges the BLM with managing wild horses and burros residing west of the Mississippi River. The agency currently manages more than 40,000 wild horses and burros in 10 Western states; another 50,000 animals reside in BLM long- and short-term care facilities.

In 2010, the BLM asked the independent nonprofit National Academy of Sciences (NAS) to review technical aspects of the wild horse and burro program and to make recommendations for future management techniques. The $1.5 million study began in 2011, and results were released in 2013.

In it’s report, NAS said the population of wild horses under BLM care on Western public rangelands increases by an unsustainable 15% to 20% annually. The report also said the BLM has not used scientifically rigorous methods to estimate wild horse and burro populations on each range, or to model the effects of management actions. Finally, the report said the BLM failed to effectively use contraception tools, specifically porcine zona pellucida (PZP) vaccines for mares and a chemical vasectomy vaccine in stallions, to achieve appropriate population control