Genetically engineered (GE) feed and glyphosate residues in feed have not, for good reason, been big topics of conversation over the last 17 years in animal science circles but, nevertheless, both were re-examined at the American Society of Animal Science (ASAS) meeting in Baltimore, Md., in a session focused on feeds derived from innovative breeding techniques.
GE feed crops became widely adopted following their introduction in 1996. Today, more than 90% of sugar beet, soybean, cotton and corn acreages in the U.S. are planted with GE varieties.
It is estimated that 70-90% of GE crop biomass has been consumed by multiple generations of food-producing animals for the past 20 years.
Amy Young of the University of California-Davis noted in her presentation on the impact of animal performance, health and products that numerous studies have shown compositional equivalence between GE and non-GE crops. Hundreds of peer-reviewed studies have shown no deleterious health effects associated with feeding GE crops to livestock, Young said.
Additionally, Young said, available U.S. Department of Agriculture productivity trends and health metrics for the different livestock industries over the past two decades do not show unexpected perturbations following the introduction of GE crops into the U.S. feed supply.
According to Young, neither recombinant DNA (rDNA) nor protein from GE feed crops are reliably detected in the milk, meat and eggs from livestock that have been fed GE feed. Studies have shown that DNA from GE crops is chemically equivalent to DNA from non-GE crops, and both are broken down the same way during digestion. The total amount of plant DNA remaining in animal feed is dependent upon many factors, including how the feed is processed. In feed from GE varieties, rDNA makes up only a fraction of the total genomic DNA, she said.
As part of the natural digestive process, Young explained, dietary DNA has been shown to move across the intestinal wall. There is no evidence suggesting DNA or rDNA transfer from plants to animals, she said.
Since dietary DNA and protein cannot be reliably detected in animal products, and considering the wide trade and usage of GE feeds globally, managing separate supply chains to satisfy mandatory labeling requirements for products from animals that consumed GE feed would be complicated and expensive, Young pointed out. There would be no food safety benefit from the substantial costs associated with segregating milk, meat and eggs from animals fed GE feed due to the fact that such products are both compositionally and analytically indistinguishable from those derived from animals fed non-GE crops, she concluded.
Glyphosate residues in feed
Dr. Dan Goldstein, distinguished science fellow and lead of medical sciences and outreach for Monsanto in St. Louis, Mo., talked about the widespread confusion that exists on pesticide residue tolerances in feed and food. He said assumptions that tolerances are safety-based limits and that exceeding those limits will result in a risk of illness in animals or humans are generally incorrect.
Tolerances are set based on actual residue values following proper application in accordance with label instructions and are designed primarily to enforce proper application, Goldstein said. He explained that although tolerances in feed must ultimately protect both animals and consumers of meat, milk and eggs, the large majority of tolerances fall far below any level of safety concern.
Animal feed efficiency and other data demonstrate no adverse effects of glyphosate residues (or GE crops) on animal performance measures, Goldstein noted. Furthermore, he said, actual measurements of glyphosate in meat, milk and eggs are generally undetectable, and overall human intake is far below levels of regulatory concern.