Per acre doesn't work. If the association is recommended that cattle Animal Unit Months be applied to bison they are providing bad info in my opinion. Though probably calculated from domesticated bison, the National Range and Pasture Handbook provides AUM equivalents for many species. The range of values for bison are 0.65 to 1.65 that of cattle depending on time of year and sex/age/condition of bison. FWIW...