vise because the control diet should have the same nutritional characteristics as the control diet.

It has been suggested (for example, Health Canada 1994) that in cases of foods where the concentration of substances to be tested cannot be increased, it would be useful to test the plant material in longterm feeding experiments with animals whose natural diets consist of large quantities and the type of plant material being tested. Research on longterm feeding of transgenic pest-protected plants to those animals (for example, grain and forage crops to livestock) might provide information relevant to human health effects (see also section 3.4). Such testing has been shown to be practical with herbicide-tolerant soybean (Hammond et al. 1996), and with Bt corn (Jackson et al. 1995). Livestock that are normally fed on the crop in question can be fed on the genetically altered variety from weaning until a termination time consistent with normal agricultural practice. The genetically closest variety can be used as a control. These types of studies would make use of the natural diet of the test organism to test large quantities of the whole plant. Nonmodified plant varieties that were identical to the genetically modified plant before the modification occurred should be used as controls. Most toxicity testing is conducted using the purified plant-pesticide (section 3.1.3), and therefore pleiotropic effects of the genetic modification cannot be monitored. If proper controls are used, feeding whole plants to the test animals might allow for the detection of potential toxicity due to pleiotropic effects.

However, there will be a need to carefully assess the relevance of such testing to human health. Humans and ruminants have different digestive systems, as humans are mongastric and ruminants have a four-chambered stomach that can serve as a buffer from the effects of some proteins. Feeding studies using monogastric animals, such as hogs, whose natural diets consist of the transgenic crop in question may provide more relevant information. While the finding of negative effects in such livestock tests would certainly raise concerns, the finding of no effects on these animals is hard to interpret because we lack sufficient information on their biochemical similarities to humans.

Is the Physiology of the Plant Changed by the Genetic Modification?

Potential pleiotropic effects of genetic modification on plant physiology and biochemistry are discussed below. The committee concludes that

It is important to monitor for physiological and biochemical changes during the development of transgenic pest-protected plants.

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