Animal Unit Equivalents

Animal Unit Equivalents

Animal unit equivalents (AUE) have been developed to standardize grazing demand among different herbivore species. An AUE expresses the quantitative forage demand of a particular kind and class of animal relative to that of an animal unit, based primarily on metabolic bodyweight (Table 1).

Table 1.
Suggested Factors Describing Animal Unit Equivalents for Various Herbivores
Type of Herbivore Animal Unit Equivalents
Mature Cow, Non-Lactating 1.0
Sheep, Mature, Non-Lactating 0.2
Ewe and Lamb Pair 0.3
Saddle Horse, Mature 1.25
Elk, Mature 0.65
Mule Deer, Mature 0.23
Whitetail Deer, Mature 0.17
Antelope, Mature 0.17

Source: Vallentine (1990), p 279.

In reality, however, AUE provides a poor basis to express carrying capacity in relation to different animal species because dietary preferences are ignored. For example, although AUE suggest that about 5 deer confer the same grazing demand as 1 cow (Table 1), their different diet (deer prefer browse and cattle prefer grass) means that this direct substitution is rarely observed. Furthermore, inventories conducted to determine biomass of available forage often focus on a particular land use, such as cattle grazing, and plants important to other herbivores may be excluded from the sampling protocol.

References and Further Reading

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Hansen, R.M., R.C. Clark, and W. Lawhorn. 1977. Foods of wild horses, deer, and cattle in the Douglas Mountain area, Colorado. Journal of Range Management 30:116-118.

Hobbs, N.T., and L.H. Carpenter. 1986. Viewpoint: Animal-unit equivalents should be weighted by dietary differences. Journal of Range Management 39: 470-471. (pdf)

Scarnecchia, D.L. 1985. The animal-unit and animal-unit-equivalent concepts in range science. Journal of Range Management 38:346-349. (pdf)

Scarnecchia, D.L. 1986. Viewpoint: Animal-unit equivalents cannot be meaningfully weighted by indices of dietary overlap. Journal of Range Management 39:471. (pdf)

Scarnecchia, D.L. 1990. Concepts of carrying capacity and substitution rations: a systems viewpoint. Journal of Range Management 43:553-555. (pdf)

Scarnecchia, D.L., and M.M. Kothmann. 1982. A dynamic approach to grazing management terminology. Journal of Range Management 35:262-264. (pdf)

Smith, A.D. 1965. Determining common use grazing capacities by application of the key species concept. Journal of Range Management 18:196-201. (pdf)

Society for Range Management. 1989. A Glossary of Terms Used in Range Management. Society for Range Management. Denver, CO. 3rd ed. p. 3.

Vallentine, J.F. 1990. Grazing Management. Academic Press. San Diego, CA. pp 278-280.