It is a simple concept: the forage (grass, forbs, shrubs) consumed by domestic livestock is not available as food and cover for native wildlife-species that are ecologically significant, admired by wildlife enthusiasts, and prized by hunters. Range managers use the rather imprecise animal unit month or AUM to measure and allocate forage. An AUM is the amount of forage necessary to sustain a cow and calf for one month (approximately 650 pounds, although some estimates are more, between 800-1000 pounds 1). Below are generally accepted AUM equivalents.
Wildlife Animals Per AUM Livestock Animals Per AUM Bighorn Sheep 6.9 Cow 1 Pronghorn 10.8 Horse 0.8 Mule Deer 7.8 Goat 5 Elk 2.1 Sheep 5 Bison 0.8 Moose 0.8
Available forage is often a limiting factor for wildlife. The species vary by habitat type, but for every domestic animal we see on public lands, we are not seeing - and the ecosystem has been deprived of-the commensurate number of native wildlife. Not only do livestock compete with wildlife for food, but also for space and water.
1. GAO. 1988. Public rangelands: some riparian areas restored but widespread improvement will be slow. RCED-88-105. General Accounting Office. Washington, DC: 12.