Management of the Pryor Mountains horse herd has focused on fulfilling the Free-Roaming Wild Horse and Burro Act's requirement that BLM maintain a thriving natural ecological balance. In general, BLM initially focused on how many horses the range could support and in maintaining conformity to the Pryor Mountains standard. However, with the development of DNA testing in the mid-1980s, the focus changed to maintaining the herd's genetic viability as well. In 1988, researchers at Washington State University published a paper that raised concern that the herd exhibited a lack of genetic diversity, and could be suffering from genetic drift and/or a population bottleneck. BLM contracted with veterinarian E. Gus Cothran (then at the College of Veterinary Medicine at the University of Kentucky, but now at the Texas A&M College of Veterinary Medicine & Biomedical Sciences) to take random genetic samples of the herd in 1994, 1997, and 2001. Cothran's analysis found no evidence of a bottleneck. Genetic diversity was above the mean for feral horse herds in the United States, and just below the mean for domesticated breeds. The BLM, however, interpreted these studies in 2009 to indicate that the genetic diversity of the Pryor Mountains herd is well above the mean for domestic breeds. Cothran considered the herd to be in genetic equilibrium, although he cautioned that a minimum of 120 breeding-age animals should be kept on the range to maintain the genetic health of the herd. Research by biologists and veterinarians at Colorado State University, the University of Kentucky, and other colleges found that there is little inbreeding in bands, as the stallions tend to drive off colts when they are about two years old.