An Animal Unit Month (AUM) is the amount of forage consumed by one wild horse or one cow/calf pair in one month. It also represents the amount of forage consumed by two wild burros or five sheep in one month.
The Appropriate Management Level (AML) corresponds to the number of wild horses or burros allowed in a given area by plan.
AMLs are usually not specified for cattle and sheep.
Wild horses and burros graze twelve months per year. To convert horse AMLs to AUMs, multiply the AMLs by twelve.
Wild Horse AUMs = AML × 12
The Challis HMA, in the news recently, has an AML of 253. The forage allocation for horses there would be 3,036 AUMs per year.
To convert burro AMLs to AUMs, multiply the AMLs by twelve and divide by two.
Wild Burro AUMs = AML × 12 ÷ 2
At the Twin Peaks HMA, 116 wild burros are allowed by plan. The forage allocation for those animals would be 696 AUMs per year.
If you know the AUMs and want to determine the AMLs, just reverse the math.
Wild Horse AML = AUMs ÷ 12
Wild Burro AML = AUMs ÷ 12 × 2
The AUM budget for horses at Warm Springs HMA is 2,424 AUMs per year, therefore the AML must be 202. It has nothing to do with the carrying capacity of the land.
Western Horse Watchers Association 