For a quick estimate, convert the livestock AUMs inside the HMA to wild horses and add the result to the AML.
Livestock receive 3,646 AUMs per year inside the allotment and the allotment is about three times larger than the HMA, so the forage assigned to livestock inside the HMA should be about 3,646 ÷ 3 = 1,215 AUMs per year, assuming the resource is evenly distributed across the parcel.
That forage would support an additional 1,215 ÷ 12 = 101 wild horses, for a True AML of 35 + 101 = 136.
The stocking rate at the new AML would be 5.8 wild horses per thousand acres, or 172 acres per horse.
The target rate across all HMAs is one wild horse per thousand acres, because they are managed primarily for livestock.