Science in Society Archive

GM food safe?

Recent incidents and scientific findings cast grave doubts over the safety of GM food and feed. We shall be circulating a selection of the following reports.

  1. Cows Ate GM Maize & Died
  2. Transgenic DNA and Bt Toxin Survive Digestion
  3. Bt Toxin Binds to Mouse Intestine
  4. Syngenta’s Spanish GM Trojan Horse
  5. Liver of Mice Fed GM Soya Works Overtime
  6. Animals Avoid GM, for Good Reasons

Animals Avoid GM Food, for Good Reasons

Experimental and anecdotal evidence shows that animals seek to avoid GM food and do not thrive if forced to consume such food. Dr Eva Novotny reports.

In the course of preparing a submission to the public hearing on a genetically modified (GM) maize that the UK government wanted to put on the National Seed Register, I had the opportunity to review evidence on how animals respond to GM food. The evidence makes interesting reading.

Chardon LL experiments

Chardon LL is a GM maize engineered for tolerance to the herbicide glufosinate. The whole plant is intended as cattle-feed, but no experiments on whether this is safe or suitable has been carried out.

Approval of the application of Aventis for commercial growing of this maize in the UK was granted on the basis of two animal-feeding experiments, one on feeding kernels to chickens and the other on feeding the isolated GM protein to rats. In both experiments, the investigators concluded that the tested animals consumed food and gained weight normally.

However, reanalysis of the data led to a different conclusion.

The first experiment fed Chardon LL maize kernels to 280 young broiler chickens over 42 days, purportedly to detect differences in nutrient quality of corn samples. All the chickens were allowed to eat at will.

The official report said: “Results of live bird traits … show that source of corn … had no effect on body weight, feed intake, … or percent mortality over the experimental period …” and “Glufosinate tolerant corn from the U.S.A. is comparable in feeding value, for 0-42 day broilers, relative to the commercially available corn hybrid. Therefore, the nutritive value of glufosinate tolerant corn hybrid is equivalent to a commercially available corn hybrid.” The mortality rate was judged to be normal.

Closer examination of the data shows up many unexplained anomalies.

Although chickens on the GM diet have, on average, weights only 1% below the average weight in the control group, the error bars are much wider for chickens fed GM maize; and they grow progressively wider as the experiment progresses.

During the first phase of the experiment (days 0-18), the test group eating GM maize consumed 9 gm more than the control group; during the second phase (18-32 days), consumption had dropped to 7 gm less; and in the final phase (days 32-42) consumption by the test group had fallen to 63 gm less than that of the control group. Again, the error bars are much greater for the test group and increase with time.

Average body weights and feed intakes of the chickens do not vary significantly, as concluded in the study. Nevertheless, the much larger error bars for both these quantities give concern that the weight gains and the feeding patterns were erratic in the treated group, indicating that at least some of the chickens were not thriving on the glufosinate-resistant maize.

Information on deaths during the study is given only in the form of mortality: 7.14 ± 5.47 % for chickens eating the glufosinate-resistant maize and 3.57 ± 4.29 % for those fed commercial hybrid corn. Although the former values are twice those of the latter, the study points out that values of 5 to 8 % in male broilers are normal at that laboratory.

Nevertheless, it may be significant that the mortality rate was twice as high among the chickens eating the GM maize as compared with those fed commercial non-GM hybrid maize.

Another experiment involved feeding PAT-protein to rats. This study on rats, like that on chickens, has little relevance to cattle, as the digestive systems of these animals are very different. Furthermore, it was not the Chardon LL maize itself, but the isolated PAT-protein it contains that was tested; and the effects of feeding the isolated protein must be expected to differ from the effects of feeding the whole maize.

Also, the very short time during which the experiment was pursued (14 days) gives no indication of possible long-term effects of feeding over a lifetime, especially when the maize is to be fed to a very different animal species. Only five male rats and five female rats were used in each of the four groups, and the individual rats had substantial differences in weight even at the start of the experiment.

Nonetheless, the studies claimed, “Average mean food consumption over treatment was in the same range for treated groups and controls”, “Occasionally recorded differences between controls and treated groups were generally small, showed no dose-relationship or consistent trend…” and “Mean body weights were similar for treated groups and controls. There were no differences which could be attributed to treatment with the test article.”

Although the purpose of the study was to test for toxicity, the data provide evidence that the animals may not be thriving on a diet including the PAT-protein. The evidence for this suggestion comes from data on body weights and food consumption.

The 40 young, rapidly growing rats were divided into two control groups and two test groups, each containing 5 males and 5 females. All animals were allowed to eat at will.

Tables provided, separately for males and females, the average weight of each of the four groups as measured on several days of the experiment. For males eating a small amount of PAT-protein, weights remained nearly the same as for one of the control groups; while for those eating the high dose of PAT-protein, weights fell progressively below those of all other groups, even though these rats were marginally the heaviest group at the beginning of the experiment. Females in both groups consuming PAT-protein had weights falling gradually below those of the two control groups, although the females fed the high dose were the heaviest group at the beginning. For both males and females consuming high-doses of PAT-protein, weight gain per day, averaged over the duration of the experiment, was distinctly lower than for either control group.

During the latter half of the experiment, data for individual animals show that 2 males and 2 females on the low-PAT-protein diet were rapidly falling behind in weight as compared with other rats in the same group and in both of the two control groups. Of the rats on the high-PAT-protein diet, 3 males and one female were falling behind in weight during the latter half of the experiment.

While these data are not conclusive because too few animals were studied over too short a time, the low rates of weight-gain in several of the animals eating PAT-protein suggest that some individuals were not thriving on the diets that included PAT protein.

The data also showed unusual patterns in the food intake, averaged over the group, of animals consuming the high dose of PAT-protein, suggesting that the diet did not suit the rats. In the middle of the experiment, both males and females on this diet had an increase in food intake followed by a dip, unlike the other groups; then, over the last five days, their food consumption showed a sharp rise, again unlike other groups.

Stray cattle did not eat GM maize

The following press release -‘Damage To Gm Maize National List Trial Site’ - was issued by the then Ministry of Agriculture, Fisheries and Food on November 10, 2000:

“The NIAB (National Institute of Agricultural Biotechnology) have notified MAFF of damage to a national list trial of GM forage maize taking place in Somerset. The damage was caused by cattle straying onto the site in October. There is no evidence that the cattle ate any of the maize.

“Sheridan - the maize in question - has full approval under European GM legislation to be marketed for both animal and human food use. The undamaged maize at the site has since been harvested.”

Sheridan is a GM forage maize that contains the same genetic construct (conferring herbicide tolerance) as Chardon LL. It is interesting to note that the cattle did not wish to eat any of the maize.

‘When the Corn Hits the Fan’

American journalist Steven Sprinkel wrote an article with the above title in an ACRES, USA Special Report dated 19 September, 1999 (reproduced on the Natural Law Party Wessex website,, which contains the following excerpt.

“After four months of retrieving anecdotes from Kansas to Wisconsin, I think its high time to sample the producer community more thoroughly to see how many stories are out there. About the hogs that wouldn’t eat the ration when the GMO crops were included. About the farmer who said “Well, if you want your cattle to go off their feed, just switch them out to a GMO silage.” About the farmer who said that his cattle broke through an old fence and ate down the non-GMO hybrids but wouldn’t touch the Round-up ready corn, and as a matter of fact “They had to walk through the GMOs to get to the Pioneer 3477 on the other side.” About the cattleman who saw the weight-gain of his cattle fall off when he switched over to GMO sources. About the organic farmer with a terrible deer problem on his soybeans, and when he drives out at night there are forty of them mowing down his tofu beans while across the road there isn’t one doe eating on the Round-up Readies. About the raccoons romping by the dozen in the organic corn, while down the road there isn’t one ear that’s been touched in the Bt fields. Even the mice will move on down the line if given an alternative to these “crops”. What is it that they know instinctively that most of us ignore?”

Other incidents of cattle refusing to eat Bt maize

Various scientists working actively with the farming community in the United States have reported difficulties feeding GM maize to cattle. In April 2000, one of them (who has asked to remain anonymous) sent the following information:

“There have been dozens of such reports over the last two years. Generally, the reports are concerned with Bt maize. Many farmers feed maize to their cattle just as it grows, without mixing in other feedstuffs. Typical reports are that the farmer buys a new shipment of maize, which his cattle either refuse to eat or eat with reduced consumption. Upon making enquiries, he discovers that the maize is a genetically modified variety. When he replaces it with a non-modified maize, the cattle start eating again.”

Scientific evidence for animal preferences

Although it may be difficult to credit animals with the ability to distinguish between GM and non-GM feed, this anecdotal evidence is supported by scientific evidence that they can indeed distinguish between organically- and non-organically-produced feed; moreover, they have a definite preference for the former (see “Do animals like good food?” this issue).


Re-analysis of experiments on chickens and on rats fed Chardon LL GM maize suggest that, contrary to the official conclusions, at least some individual animals do not gain weight as rapidly as they should when given a diet including GM feed. Furthermore, there appear to be irregularities in the feeding habits of at least some animals given GM feed. In the experiment on chickens, mortality was twice as high among those fed the GM maize as among those fed non-GM maize.

Existing scientific evidence indicates that farm animals prefer organically produced over conventionally produced feed; while a substantial amount of anecdotal evidence on both domestic and wild animals indicates that, given a choice, they will avoid GM feed and, if forced to eat GM feed, they do not thrive.

(This is an edited version of Report for the Chardon LL Hearing: Non-suitability of genetically engineered feed for animals, by Eva Novotny, Scientists for Global Responsibility, May 2002.)

Article first published 13/12/03

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