Long-term study in mice

"GM maize causes impotence" Or: How a scientific study is used for political motives.

A long-term feeding study in mice has reignited the debate about the safety of genetically modified maize. Laboratory mice that were fed a particular type of GM maize produced fewer offspring. While scientists warned against drawing premature conclusions and called for further research, GM opponents saw the study as proof of the danger of GM maize.

In the study, which was commissioned by the Austrian Ministry of Health, Family and Young People, laboratory mice were given a diet that included one-third genetically modified maize NK603 x MON810. A control group was given a closely related (isogenic ) maize line. In one part of the trial, a conventional maize variety grown in Austria was also fed to the mice. The study looked primarily at the number, weight, growth and survival rate of the offspring. Reproduction is regarded as a sensitive parameter for possible long-term effects.

Long-term feeding trial with mice: No abnormalities, but fewer offspring in the third and fourth litters.

Feed: One group of mice was given feed that consisted of one-third NK 603xMON810 maize. This GM maize is a cross between a herbicide-resistant maize and an insect-resistant maize that is authorised for use as food and feed in the EU.

The study was conducted by a working group at the University of Veterinary Medicine in Vienna and was led by Prof. Jürgen Zentek. Two designs were used:

a multi-generation study (MGS) in which the mice in the various feeding groups were studied over four generations
and reproductive assessment by continuous breeding (RACB) with four litters from the same parents.
In the multi-generation study, the groups in the first generation consisted of 18 pairs of mice. The groups in the subsequent generations consisted of between 20 and 22 pairs. In the RACB trial, each group consisted of 24 pairs. The mice used came from 'outbred' strains, where the individual differences between individual mice are greater than with the frequently used inbred strains. Results obtained using outbred strains must take account of the greater variability of the individual mouse genotypes.

Mice: Fewer offspring in the third and fourth litters

The multi-generation study found no significant differences between the mice in the different feeding groups. This was not the case in the RACB, however. The results of this test "provide a wide range of differences between the feeding groups that appear higher than natural variations normally expected, "according to the authors of the study.

Significantly fewer offspring were born in the third and fourth litters. Their weight was also lower. Overall, the group fed on GM maize produced fewer litters. Since there was no difference between the diets of the different mouse groups in terms of energy and nutrients, the study authors speculate that the effect was caused by a "factor beyond nutrient supply". Whether the lower reproduction performance can be attributed to the genetic modification or whether it is an unintended effect related to the crossing of the two GM maize lines NK603 and MON810 (gene stacking) "has to be further evaluated".

Additional studies were only carried out on the mice of the multi-generation study.

For females of the second and later generations, and males of the third generation, the kidney weights of the group fed on GM maize were significantly lower than for those of the control group.
Although the liver weights of the females differed between the various groups, the differences were not unidirectional and therefore not interpretable. The liver and kidneys are regarded as sensitive risk indicators.
No differences were found in studies of the spleen, lymphocytes and other cells of the immune system.
Examinations of certain cell structures under the scanning electron microscope did not yield any clear results.
Molecular genetic analyses of the gut tissue indicated that the interactions between feed and intestine are different in the mice fed on GM maize than in those fed on conventional maize.

Political demands prior to publication of the study

Even before Prof. Jürgen Zentek had presented his study at a public event, Greenpeace had published a first press release stating that "consuming genetically modified maize reduces fertility", and was calling on the European Food Safety Authority (EFSA) to close "because of incompetence" and for all authorised genetically modified plants to be removed from the market. The news agency Glocialist added fuel to the fire with its headline "Gen-Mais macht impotent" (GM maize causes impotence). Austrian politicians from all political parties saw their ‘serious misgivings’ about genetic engineering in agriculture justified.

It was only later that the Austrian Agency for Health and Food Safety (AGES), which had organised the conference at which the study was first presented, clarified that the study was an individual case study and that the results should not be applied to humans. According to Jürgen Zentek, the preliminary results of the study urgently need to be validated by further studies. He adds, however, that multi-generation studies have been shown to be suitable for revealing the impact of feed on mice.

So far, the feeding study has been published only in the form of a research report, but not in a recognised scientific journal. The European Commission has since asked the Austrian government to send it the study. EFSA will then an pass expert opinion on it.

"GM maize causes impotence" Or: How a scientific study is used for political motives.

Mice: Fewer offspring in the third and fourth litters

Political demands prior to publication of the study

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