Dead dairy cows: Bt maize under suspicion
On a farm in Wölfersheim, Hessen, twelve dairy cows die within the space of two years. They have been partly fed on genetically modified Bt maize. The farmer suspects that Bt maize has caused the deaths. A Report-Mainz TV programme broadcast by the television channel ARD in December 2003 also finds serious safety lapses and criticises the authorities for their inaction. However, the authorities consider infectious diseases and deficiencies in the composition of the feed to be a more likely explanation.
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Between 1997 and February 2002, farmer Gottfried Glöckner of Wölfersheim in Hessen fed his dairy cows with increasing amounts of genetically modified Bt maize which was being tested on his farm as part of authorised field trials. In 2001, five dairy cows died and by October the following year seven more had died. Glöckner suspected that the Bt maize might be the cause of their death, particularly the Bt toxin , an active substance produced by the maize as a defence against the European corn borer and which is deadly to this pest. |
Three months after the last of the five cows died, Glöckner informed the Robert Koch Institute (RKI) in Berlin, which was the body involved in authorising EU-wide use of Bt176 maize developed by the agro-biotech company Syngenta. The RKI started an investigation and interviewed various experts in state-run and private research institutes.
Poor feed, sick animals
In April 2002, samples of Bt maize silage and Bt maize kernels from 2000 and 2001 were examined on the farm, and also other feeds used there, such as grass silage and a high-energy concentrate for dairy cattle. Glöckner had been feeding his cows on these shortly before the first problems with their health became apparent.
In their report, the experts criticised inadequacies in the quality of the feed and deficiencies in the composition of their feed rations, which they considered might lead to substantial health problems in dairy cows. They identified the following points:
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Raised levels of certain fungal toxins (mycotoxins ) in the high-energy concentrate and in the maize silage,
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Poor feed quality of the grass silage used,
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Significant changes to the feed within too short a space of time and also insufficient quantities of the minerals required by cows in the periods before and immediately after calving,
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Obvious overfeeding (around 25 percent excess energy and up to 42 percent excess protein) with consequent overweight, which in dairy cows especially can lead to metabolic disturbances and calving problems.
Two of the dead cows were examined for signs of the botulism pathogen, Clostridium botulinum, and in both cases it was found in the gut. This disease can spread amongst an entire herd and lead to death within weeks or months. Infection was also found in three of the five surviving cows.
Analysis of the findings did not provide any evidence that Bt maize was the cause of death. According to the Robert Koch Institute, "based on the data and information available, it is therefore highly unlikely that there is a causal connection between the use of feed (silage, maize kernels) containing the Bt toxin from Bt176 maize and the deaths on Glöckner’s farm. Any long-term effect leading to deaths in cattle as much as several months after discontinuing use of these feeds is at least as unlikely".
Livestock is fed Bt maize worldwide
Although Bt maize is grown annually on almost ten million hectares of land worldwide, problems of this kind have not so far come to light elsewhere. In Spain, Bt176 maize has been harvested since 1998 for use as animal feed on at least 22,000 hectares. Ana Fresno of the Spanish environment ministry confirmed that there have been no noticeable illnesses or deaths in animals fed on Bt maize.
Long-term feeding studies carried out in 1999 at the Federal Agricultural Research Centre (FAL) likewise produced no evidence of damage to health. Beef cattle fed on Bt maize showed no noticeable problems compared with conventionally-fed animals, even after 246 days. There was also no difference in fattening performance and slaughter yield. During feeding experiments on small mammals carried out as part of the authorisation procedure for Bt maize, not a single case was found of negative effects on the animals.
No evidence of risk from Bt toxin in the body
Animals fed on Bt maize also ingest the Bt toxin. This protein makes the maize resistant to certain pests. Although the Bt toxin is quickly broken down in the body by saliva and digestive enzymes, there is evidence of the protein throughout the entire digestive process.
A precondition for the authorisation of genetically modified Bt plants is evidence that the Bt toxin is harmless to animal health – and in the case of food, also harmless to human health. Feeding experiments are carried out for this purpose: rats, mice or guinea pigs are fed a Bt diet in accurately metered doses. Observations are then carried out to find the dose required to produce any effect. Toxicological tests of this kind are normal with, for example, the authorisation of additives or pesticides.
When cows eat Bt maize, a proportion of the Bt toxin ingested is present in their digestive tract. This is borne in mind during the safety assessment, as evidence must be provided that the Bt toxin ingested along with the food is harmless to health. The safety assessment is carried out under the assumption that the Bt toxin in the body is not broken down immediately and completely.
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