Case Studies

Case Studies on potential risk Scenarios and associated health indicators of livestock animals consuming GM feeds

Summary of WP3 [+]:

To identify potential health indicators that could be used to gauge health impacts of GM feed consumption on animals during post-market monitoring was the objective of Work Package 3. Four plausible scenarios of potential health impacts, including both potentially positive and adverse effects, were explored in more depth. The findings of these explorations are summarized in a final report delivered by this Work Package. The four scenarios investigated as parallel case studies thus included:

• Feed allergies in livestock: The potential allergenicity of a GM product is a commonly assessed item in the safety assessment of GM crops according to a weight-of-evidence approach, considering both the newly expressed proteins present in GM crops as well as possible changes to the intrinsic allergenicity of the host crop. Besides allergies in human consumers, also domestic animals might develop such reactions. The report recommends that appropriate models representative of livestock animals are developed, and concludes that the impact of genetic modification on the intrinsic allergenicity may be limited compared to other factors. Allergic and intolerance reactions in livestock may not be always linked to specific IgE-levels in sera which anyway would be difficult to measure and therefore additional criteria should be taken into account for monitoring purposes. Case-control studies could help focusing on specific animal populations at risk and production systems.

• Horizontal gene transfer: The issue of potential horizontal gene transfer is commonly considered during the environmental risk assessment of GM crops, in particular for the presence of certain antibiotic resistance genes in GM crops, which are used as marker genes. While the transfer of such genes from plants to microorganisms other than via homologous recombination has not been observed. Also the selective advantage imparted by the transferred gene on the recipient is a factor determining the likelihood and risk associated with such a transfer. The report concludes that for the current GM crops, the unintended plant-to-bacteria transfer will be a rare event and unlikely to pose health concerns.

• Altered levels of mycotoxins: Various scientific studies and surveillance reports suggest that, under particular conditions of insect damage and (consequently) mould infestation to pest-insect-protected GM crops, the levels of certain mycotoxins may be lower than in conventional non-GM maize. While this would be a secondary effect of the insect resistance, impacts on livestock performance and health following consumption of feeds with altered mycotoxin levels can be envisaged and therefore the topic would lend itself for further exploration. While the report concludes that there is some evidence indicating lower fumonisin levels in insect-protected GM Bt crops, a more in-depth research will be needed to study the relationship between such crops and mycotoxin contamination, and the possible use of biomarkers for health impacts. Aflatoxins and fumonisins are considered to be the mycotoxins of interest for monitoring in dairy cattle and pigs, respectively, with the advantage that aflatoxins and their impacts on livestock can be monitored throughout the production chain.

• Nutritionally altered GM crops: Various nutritionally altered GM crops are currently in the pipeline or close to marketing, in which alterations include changed levels of essential nutrients or changed bioavailability (for example, for phosphorus by adding the enzyme phytase). The report considered the various scenarios and acknowledged that the impacts of these crops are amenable to monitoring to different degrees depending on the modification. For example, while the impact of GM crops with an altered fatty acid content can easily be overruled by other factors (as the fat-extracted by-product is probably the product used in animal feed), the impact of altered amino acid composition could be monitored for in fast-growing animals. Phosphorous availability based on phytase-expressing GM crops would be amenable to monitoring so as to verify whether it is not negatively affected by the variability in phytase expression in feeds. Symptoms in rapidly growing animals (e.g., skeletal malformation, locomotion) may not be specific enough and case-control studies may be warranted in these cases.