will be identified in the development of the transgenic lines. Should products from such individuals be released to commercialization channels, they could pose a food safety concern unless the protein of concern is screened for and found absent. It is expected that well-established transgenic lines to be used in routine production will have been subjected to selection, and that concerns posed by unstable or ectopic gene expression will have been addressed to a large degree. Should pharmaceuticals or other biologically active proteins enter the food supply through products of such animals, associated food safety concern could be high. Additionally, the effects of transgene expression on animal wellbeing might indirectly affect the safety of food products derived from their tissues through stress-mediated mechanisms.

Expression of transgenes also might be intended to change the nutritional attributes or improve the safety of food products. For example, expression of transgenes in milk might optimize milk composition, add neutraceuticals to milk, or reduce the incidence of infectious disease (Zuelke, 1998; Houdebine, 2000). Several systems are being developed to reduce lactose concentration in milk (Alton et al., 1998; Whitelaw, 1999). Secretion of bovine -lactalbumin (an enzyme) in pig milk increased piglet growth (Bleck et al., 1998; Wheeler, 1994), showing the potential for changing the nutritive value of milk. Immunoglobulin A directed against viruses infecting the digestive tract might be expressed in milk (Saif and Wheeler, 1998; Castilla et al., 1998; Sola et al., 1998), and viral antigens activated by oral administration might be used to vaccinate humans and animals against viral disease (Houdebine, 2000). Changes of these types raise a moderate level of food safety concern. Claims of nutritional attributes, safety, and efficacy of milk or other food products from transgenic animals must be demonstrated.

Animals might be developed to produce food products designed to fit special human dietary needs. Possible future products might include milk that lacks the most common allergenic protein, eggs that are lower in cholesterol, meat with enhanced vitamin content, or fat content modified in quality or quantity (Young, 2002). The nutrient profiles of meat and animal products are well documented, and changes in this profile raise concerns. Changes might be unwanted by some consumers, and might add value for others. If these changed products were labeled in order to appeal to targeted consumers, and identifiable to those who have medical or other reasons to avoid such foods, they would be of low concern. Novel proteins also can be produced by genetic engineering. Although proteins are necessary components of the human diet, they can exert undesirable effects, including: (1) allergenicity and hypersensitivity, (2) bioactivity, and (3) toxicity.

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