Farming Systems

There are around 1.3 million farms in the United States that carry livestock. The majority of farms are grazing enterprises, but more than 20% of farms carry fewer than 25 grazing animals—these include hobby farms, cropping farms, and small holdings. Approximately 20% of farms house the animals— generally intensive chicken and swine systems, as well as some dairy systems (Kellog, 2002).

There are around 95 million cattle (of which around 10 million are dairy cattle) and 60 million swine currently in the United States. Broiler chicken production is around 7 billion birds per year within the United States (Figure 7.1). Almost 1 million horses are involved in the racing industry (American Horse Council; http://www.horsecouncil.org/statistics.htm).

We limit our discussion below to terrestrial animals, but fish (as suggested by Table 4.5 in Chapter 4) are of increasing

1980 1985 1900 1905 3000 2005 2010 FIGURE 7.1 Livestock inventories and broiler production. (From Office of the Chief Economist and World Agricultural Outlook Board, 2005.)

importance as a food source. The unique features of the aquatic environment drive the development of new epidemi-ological methods and biosurveillance practices relevant to that industry (Georgiadis et al., 2001). Similarly, agricultural systems are continuously evolving, and part of the evolution is the farming of previously untried species of animal and fish.

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