ABSTRACT This article considers safety aspects related to the feeding of genetically modified (GM) crops to farm animals, based on experiences in the United Kingdom, where several food scares, including bovine spongiform encephalopathy, have increased public awareness over food safety and systems of livestock production. Issues addressed include the feeding of GM crops to livestock in relation to effects on animal health and performance, the possible transfer and accumulation of novel DNA and(or) proteins in animal products, and safety aspects associated with humans consuming foods derived from animals receiving GM feeds. The impact of feed processing, including grinding, milling, heating, and steam pressure, on plant DNA integrity is considered, concluding that heat (> 95°C) and high pressure substantially disrupt plant DNA but grinding has no effect. There is no clear evidence that ensiling of forages causes significant disruption of plant DNA. The digestive processes of ruminants and nonruminants are highlighted with specific reference to the fate of DNA and RNA within the alimentary tract. Extensive degradation of DNA and RNA occurs within the rumen, but the concomitant synthesis of microbial nucleic acids results in more than 80% of the nucleic acids entering the intestines being of microbial origin, with little evidence of direct incorporation of plant DNA by the microbes. Evidence is presented of extensive degradation of microbial (and surviving plant) nucleic acids in the small intestine. Studies designed to examine the effect of GM feeds on animal performance are reviewed, providing no evidence that chemical composition, feed intake, meat, milk, or egg production are affected compared with non-GM equivalent feeds. Several studies have failed to detect the presence of novel DNA and(or) proteins in animal products, but evidence of plant DNA fragments in white blood cells and chicken tissues from other studies is presented. Finally, the article considers the improvements in analytical procedures to detect GM fragments in animal tissues and products but urges caution with respect to overinterpretation of the data, where the presence of DNA fragments does not confirm functional integrity, while suggesting that some results may have been affected by methodological issues.
Implications
Genetic manipulation (GM) of crops should benefit all involved in the production of food for human consumption, through reduced input costs, increased food security, and improved food quality. However, a significant part of these crops will not be consumed directly by humans but as meat, milk, and eggs derived from animals consuming diets containing GM ingredients. Evidence to date indicates that such practices present no threat to the health and well-being of the animals consuming the crops or the humans consuming the animal products. However, as more GM crops are commercialized, rigorous evaluation, similar to that already undertaken for the herbicide and insecticide tolerance traits of soybeans and corn, must be sustained, and in this respect close collaboration among all biological science disciplines will be essential.
Key Words: Eggs, Genetically Modified Crops, Livestock, Meat, Milk, Nucleic Acids, Proteins
© 2001, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2001. 79:E290-E295
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