animal health or value of animal products (improved flavor and tenderness, extended shelf life). For example, both increased phosphorus availability and improved amino acid balance reduce dietary needs and excretion of nutrients by nonruminants. Unfortunately, ruminants benefit from neither of these traits, illustrating how value of a trait can differ among end users. A product trait has value when the crop is identity-preserved during production, handling, and marketing a challenge to traditional grain handlers who blend commercial grains. Furthermore, rapid assay procedures are needed to verify presence of the desired trait.
Production of transgenic crops increased more than thirtyfold from 1996 to 2002, primarily from four crops (soybeans, 63%; corn, 19%; cotton, 13%; canola, 3% of total transgenic crops) grown primarily in four countries (United States, 63%; Argentina, 23%; Canada, 6%; China, 4% of transgenic cropland). Land area devoted to transgenic crops in the United States is shown in Fig. 1.
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