London (12.08.13) – The affair of the tumorous French rats rumbles on.

Readers may remember the claims made in September 2012 that female rats fed GM-herbicide-tolerant maize in a two–year study developed large mammary tumours almost always more often than and before controls, tumours which were the direct result of being fed that GM-maize together with or without traces of glyphosate, the controlling herbicide (1).

The paper generated a veritable storm of protest from a host of individual scientists (2) as well as from many regulatory authorities and scientific academies and societies around the world, including six academies within France itself.

The criticisms focussed on two main defects of the original study: that the strain of rats used tend spontaneously to develop tumours over a two-year life span and that the statistical data and evidence in support of the original authors’ conclusions were quite inadequate for the complexity and many variable of the original study.

But the affair did cause ructions and many individuals, organisations and media outlets jumped on a bandwagon from heaven to promote their particular causes, oblivious or uncaring about what the evidence did or did not show. It led a number of countries to ban the import of GM-products, at least, as it turned out in some cases, temporarily (3). Indeed, the announcement of the French study appears to have been planned with the objective of promoting a maximum level of confusion. The advance results were given under embargo to journalists who agreed that they would seek no other opinion and consult no specialists in the field (who, it was no doubt feared, might – indeed, as it turned out, would –take a critical view of the French study). Such a restriction on journalists’ right of consultation is very rare indeed, if not totally unheard of.

After the original embargo had expired, and critics had an opportunity to express their view, there was near universal condemnation of the study objectives and methodology as well as the claims made on the basis of the data presented.

But it was too good an opportunity for the opponents of GM-technology to allow to fade away. So recently one group has attempted to use guidelines issued by the European Food Safety Authority in a new allegation: that they validate the long-term GM feeding studies which found serious health effects from NK603 maize (4). Nine specific points were mentioned; in particular:

2. EFSA says the same strain of rat that was used in the 90-day study on the GM food should be used in the longer study - thus vindicating Seralini's use of the Sprague-Dawley rat, which Monsanto used in its 90-day study on the same maize.

3. EFSA says animals should be fed ad libitum, which Seralini did, but which critics complained made it impossible to measure individual food and water consumption.

7. EFSA recommends a minimum of 10 animals per sex per group for the chronic toxicity phase, the same number that Seralini used.

Alison Van Eenennaam, who actually knows about such matters, looked at the EFSA guidelines to find they defer to the OECD guidelines which state that “Young healthy adult animals of commonly used laboratory strains should be employed. The combined chronic toxicity/carcinogenicity study should be carried out in animals from the same strain and source as those used in preliminary toxicity study(ies) of shorter duration, although, if animals from this strain and source are known to present problems in achieving the normally accepted criteria of survival for long-term studies (see Guidance Document No. 116 (7)), consideration should be given to using a strain of animal that has a acceptable survival rate for the long-term study.”

Dr. Van Eenennaam then looked at Guidance Document No. 116 (7), which basically says “Importantly, in selecting a suitable rat strain for carcinogenicity testing, test animals should be selected that are likely to survive for the recommended duration of the study (see section 3.3.2). Britton et al. (2004) reported that of the three rat strains studied (Harlan Hsd:Sprague-Dawley SD, Harlan Wistar Hsd:BrlHan:WIST, Charles River Crl:CD), Harlan Wistar strain survived in much greater numbers in 104-week carcinogenicity studies. The improved survival rate, according to the authors, appeared to be independent of body weight and food consumption and was reflected in the spontaneous pathology profile. Other authors believe this phenomenon to be attributable to a combination of obesity and genetic susceptibility and advocate dietary restriction as a method of extending survival in long-term carcinogenicity bioassays (Keenan, 1996).

The document continues: “An important aspect of the feeding regime used in chronic toxicity and carcinogenicity is the recognized effect on study outcome of feeding ad libitum. Traditionally, maximal growth and reproduction have been used as criteria for the evaluation of laboratory animal diets (NRC, 1995). However, evidence from a number of studies indicates that restricting the caloric intake of laboratory animals may have beneficial effects on life span, the incidence and severity of degenerative diseases, and the onset and incidence of neoplasia (Weindruch and Walford, 1988; Yu, 1994; Keenan et al. 1997). Based on these results, allowing animals to eat ad libitum to produce maximum growth and reproduction may not be consistent with objectives of long-term toxicological and aging studies (NRC, 1995). Overfeeding by ad libitum food consumption is generally considered to be the most significant, uncontrolled variable affecting the outcome of the current rodent bioassay, and in particular, the correlation of food consumption, the resultant adult body weight and the 2-year survival in Sprague-Dawley rats is highly significant. (Keenan et al., 1997). However, it will probably take years to introduce dietary restriction into national and international test guidelines for toxicity testing because of concern that the delayed occurrence of, for example, cancer reflects a decrease in the sensitivity of the carcinogenicity test in detecting the carcinogenic potential of tested chemical and because the considerable database on historical control is based on data from ad libitum feeding studies (Meyer et al., 2003). Species and strain differences in survival are discussed further in chapter 3.3.”

So Dr. Van Eenennaam was able to conclude that the EFSA document suggests NOT using Sprague-Dawley rats for long term (104 week) feeding studies but rather the Harlan Wistar strain, having 50/sex/treatment group or at least 65/sex/treatment group if using Sprague-Dawley due to their known poor survival, and that ad libitum food consumption is known to be a highly significant effector on cancer and decreased 2-year survival in Sprague-Dawley rats.

Thus, Dr. Van Eenennaam is not at all sure on what planet all that equates to claims of vindication by EFSA.

Never mind, those particular points probably will not be raised again but there were six others in the article and imagination can no doubt dream up still more. They may be relevant or irrelevant to the French study or to the comments that followed. It doesn’t matter: the objective is always to muddy the waters, generate as much uncertainty as possible, waste people’s time and try to get them so fed up with sterile arguments that they will not respond to the next one.

That’s the way it is done.


1. Gilles-Eric Séralini, Emilie Clair, Robin Mesnage, Steeve Gress, Nicolas Defarge, Manuela Malatesta, Didier Hennequin and Joël Spiroux de Vendômois (November 2012). Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Food and Chemical Toxicology, 50 (11), 4221-4331

2. Multiple authors (7.11.12). Serious inadequacies regarding the pathology data presented in the paper by Séralini et al. (2012). Food and Chemical Toxicology (

3. Better ban it, it’s dangerous. Well, maybe not. CropGen (7.1.13) (

4. Seralini validated by new EFSA guidelines on long-term GMO experiments. GM Watch (5.8.13) (


  The way it is done