The HMA covers 85,407 acres in eastern Oregon, including 71,893 BLM-managed acres, 10,898 privately owned acres and 2,615 acres of Bureau of Recreation land, according to the 2017 Final EA for resource enforcement actions therein.
The 80 horses allowed by plan require 960 AUMs per year.
The stocking rate allowed by plan is 0.9 wild horses per thousand acres.
Table 3-4 in the EA supplies information for three allotments inside the HMA. The total allotment acreage is slightly less than the HMA acreage, so most, but not all, of the HMA is subject to permitted grazing.
The allotments, including current status, were discussed in this post from August 1.
The Texaco Basin permittee would have to place 2,350 ÷ 7 = 336 cow/calf pairs on the allotment to graze off 2,350 AUMs in seven months.
The stocking rate at Texaco Basin would be 336 ÷ 14,558 × 1,000 = 23.1 cow/calf pairs per thousand acres.
The total number of cow/calf pairs inside the HMA would be 1,280, with an overall stocking rate of 15.5 cow/calf pairs per thousand acres.
Western Horse Watchers usually converts AUMs to horses and cow/calf pairs, even if the HMA is designated for burros and/or the allotments are permitted for sheep. The resource requirements of wild horses and cow/calf pairs are said to be equivalent.
The stocking rates and forage allocations are compared in the following charts.
The HMA is managed primarily for livestock, contrary to §1332(c) of the statute, with the horses receiving just 10% of the authorized forage, neglecting wildlife.
The forage assigned to livestock would support an additional 705 horses, for a True AML of 785.
The pre-gather population of 450 is well within this range, so there are no excess horses, no overpopulation and no justification for a fertility control program. As usual, the advocates are wrong.
The 705 wild horses cheated out of a spot on their home range represent 1.4% of the 50,000 horses in off-range holding.