Poultry integrators, such as Pilgrim's, operate under a "vertical integration" system. The integrator provides the chicks, feed and drugs to the grower, but the grower must supply houses that meet the company's specifications. The grower is then paid on the basis of the weight of the birds at time of pick up. However, the grower is given only short contracts, usually somewhere in the neighborhood of seven weeks, or the time it takes to grow a flock. If, at the end of the contract period, the grower falls into disfavor, the company may decide not to place anymore chickens with the grower and there is virtually nothing the grower can do.
http://www.populist.com/2.96.Chicken.html

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Note added at 13 mins (2010-12-19 23:40:10 GMT)
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Poultry integrators own their own feed mills, hatcheries, processing plants as well as truck fleets to transport the feed and chickens even though they could hire out these functions. The reason is because it is PROFITABLE for the company to own these components.
http://tinyurl.com/38xwfxd