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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 435-468 in Animal Agriculture and the Environment: National Center for Manure and Animal Waste Management White Papers. J. M. Rice, D. F. Caldwell, F. J. Humenik, eds. 2006. St. Joseph, Michigan: ASABE.  .(doi:10.13031/2013.20261)
Authors:   B. Auvermann, R. Bottcher, A. Heber, D. Meyer, C. B. Parnell, Jr., B. Shaw, J. Worley

Animal feeding operations (AFOs) are a fast-growing sector of production agriculture in the United States. In general, AFOs are facilities in which livestock or poultry are fed in confined areas or buildings in which native vegetation cannot be sustained and to which manufactured, processed or mixed feed must be supplied from without. They exist and grow primarily as a result of economies of scale, affording producers the opportunity to minimize costs associated with transportation, feeding and harvest.

The concentration of animals in an AFO puts stress on the environment in several ways. Most broadly, because conversion of feed to marketable end products is inherently inefficient, AFOs tend to accumulate unused nutrients and other feed-derived by-products until they are somehow exported from the system. Moreover, because the boundary of a livestock system is of arbitrary extent, this net accumulation of nutrients or other by-products may occur at multiple scales, from the farmstead to the watershed to the geographical region depending on the relative marketability of by-products at each of those scales.

The accretion of by-products in localized areas increases environmental stress by (a) providing a reservoir of potential environmental contaminants and (b) increasing the gradient by which those contaminants can move into an otherwise nave environment. For example, accumulation of phosphorus in stream sediments may increase both (a) the concentration gradient driving the diffusion of phosphorus from the sediments into the streamflow and (b) the length of time required to deplete the phosphorus reservoir in those sediments. Virtually every environmental stress associated with animal feeding can ultimately be traced to system inefficiencies and lack of markets for the lowvalue by-products resulting from them.

One of the ascendant forms of environmental stress associated with AFOs is air pollution. Traditionally defined, air pollutants are compounds or materials that, when suspended in or mixed with air, degrade air quality and impair its utility for any of a wide range of purposes. Although the public associates air pollution most commonly with haze, smog or other low-visibility conditions, pollutants having little to no effect on visibility may threaten the health of humans, animals and other living organisms. One class of pollutants having both health and visibility implications is particulate matter.

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