Beginning in 1916, the USDA-ARS began counting livestock for all
pastures on the Jornada Experimental Range. Stocking rates are
expressed in animal unit month (AUM), which is the amount of forage
needed by an “animal unit” for one month. The quantity of forage is
typically based on the animal unit’s metabolic weight.
Cattle, horses, sheep and goats have the following equivalents: 1 cow
= 1; 1 yearling heifer = 0.8; weaning = 0.55; bull = 1.25; horse =
1.25; sheep/goat = 0.2.
Goats were few and are included as part of the sheep category and not
differentiated. Total AUM is calculated for each year for each
category of livestock from 1919 to 2001.