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Response to a feeding study in pigs by Carman et al

(July 2013)

In June 2013, Dr Judy Carman and co-authors published a paper in the Journal of Organic Systems on a feeding study in pigs. The pigs were fed either a mixture of GM corn and GM soy or an equivalent non-GM diet for nearly 23 weeks. The GM diet was derived from plant lines approved for food use in Australia and New Zealand (and in other countries).

There were no differences between pigs fed the GM and non-GM diets for feed intake, weight gain, mortality and blood biochemistry parameters but the authors attributed severe stomach inflammation and enlarged uteri to the GM diet.

FSANZ response – key points 

  • The authors have not provided convincing evidence that stomach inflammation was present. The stomach data, as presented, do not support the authors’ interpretation and conclusions because:

The presence of “inflammation” was determined by visual appearance (reddening) only, without any microscopic (histological) confirmation. This is not considered a reliable method for establishing the presence of true inflammation, because it relies solely on the colour of the tissue which can vary for many reasons.

If the GM diet caused the stomach inflammation, the total number of GM-fed pigs with stomach inflammation would be expected to be greater than non-GM fed pigs. According to the data provided however, greater numbers of non-GM fed pigs exhibited “inflammation”.

The authors erred in their statistical approach to analysing the stomach “inflammation” data. If the data are analysed using more appropriate statistical methods, no statistical association with diet exists.

  • The authors have not proved that the statistically significant increase in uterine weight is attributable to the GM diet.

The relevance of uterine weight data and the presence of fluid in uteri cannot be determined without information on the ovarian activity of the affected pigs, and without microscopic (histological) evidence to determine the condition of the endometrium. Uterine weight and fluid content can vary enormously in young female pigs based on the stage of puberty and/or their reproductive cycle.

  • There are many deficiencies with the design, conduct and reporting of the study. More detailed comment on these deficiencies  is available. These deficiencies are sufficient to invalidate the study conclusions.

  • Overall, the data presented in the paper are not convincing of adverse effects due to the GM diet and provide no grounds for revising FSANZ’s conclusions about the safety of previously approved glyphosate-tolerant and insect-protected GM corn lines and glyphosate-tolerant GM soy lines.

Read the detailed commentary

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