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why do we use rats to test gmos

Submitted by: DIanaC


Expert response from Community Manager

Friday, 30/10/2015 14:06

Current approaches in the safety assessment of genetically modified (GM) crops include animal feeding studies with processed grain or other plant parts.  A 90-day rat feeding study is one of the animal feeding/toxicity studies required by some regulatory authorities to assess safety of GM crops. Rodents are available in large quantities from commercial suppliers of animals for research purposes.  Aside from this and other practical considerations such as the ability to house and care for rodents, the metabolic and physiologic processes in a rat and human are sufficiently similar to allow for extrapolation of effects from rats to humans and to determine safe exposure levels for protection of human health. In addition, the genetic consistency of rats used in laboratory studies facilitates detection of effects related to treatment.  Therefore, the rat is one of the most important animal models in testing pharmaceuticals and chemicals for potential adverse effects and a key component in assessing risk associated with potential human exposure. 


The long history and experience in using the rat in safety assessment makes it a very well understood toxicity animal model in hazard identification and risk assessment.  Thus, a 90-day feeding study in the rat is required by some regulatory authorities to assess potential toxicity associated with repeated exposure to the processed grain or other plant parts from GM crops compared to the non-GM counterpart mixed into the rodent diet.  


However, animal feeding studies are only one part of the safety assessment of the GM crops.  Other major studies involved in safety assessment of GM crops are assessment of source of transgene, molecular characterization of GM crop, and agronomic and compositional equivalence of the GM crop and its non-GM counterpart.  Compositional analysis of plant parts is one of the most important studies performed to assess safety of the GM crops. In this study, GM and non GM crops are grown adjacent to each other at various geographical locations.  Various plant parts are collected and processed including grains. Processed plant parts are analyzed through various laboratory-based analytical methods for major and minor crop components which include, but not limited to, protein, fat, dietary fibers, vitamins, nutrients and antinutrients.  If there is no difference observed in the composition between the GM and non-GM counterpart beyond biological variability, then GM and non-GM crops are considered nutritionally equivalent or substantially equivalent. 


Animal feeding studies, including 90-day rat feeding studies, are conducted to confirm the substantial equivalence between GM and non-GM crops as well as to test any unintended effect that might have occurred during the genetic modification of the GM crop and not detected during the compositional analysis study.  Ninety-day rat feeding studies are conducted routinely as part of safety assessment of GM crops,  but in none of the studies have any adverse effect due to consumption of GM crops been observed.



Expert response from Andrew Bartholomaeus

B.Pharm, PhD, Cert Ag (III)

Friday, 23/10/2015 14:09

The genes and therefore the physiology and biochemistry of a rat, and other experimental animals, are actually very similar to humans.  Humans even have a gene for a tail but it is switched off in humans. This does not mean however that effects seen in rats are automatically relevant for humans.  Very often a careful consideration of the physiology of the rat and that of humans is necessary to determine which effects seen in rats are relevant to humans.  Equally, in order for a rat study to be scientifically credible it needs to be carefully designed, conducted and interpreted. Failure to pay attention to these details is a major flaw in those few studies that have claimed to find adverse effects in animals fed GMOs. 


Studies of whole foods in rats, as opposed to specific proteins or other constituents, are not relevant to humans because the design does not support robust interpretation.  The general safety of GMOs to humans is better assessed from compositional analysis of the modified plants and from the knowledge of the wide variation that exists in the genes and composition of all plants including food crops. A good, not too technical, paper that discusses the relevance of animals studies on GMOs is that of Bartholomaeus et al (2013) "The use of whole food animal studies in the safety assessment of genetically modified crops", Critical Reviews in Toxicology, 43 (S2) 1-24.  Another pertinent paper is that by van Eenennaam & Young 2014 "Prevalence and impacts of genetically engineered feedstuffs on livestock populations”, American Society of Animal Health 92, 4255-4278. This paper looks at the use of GM foods in livestock production in the USA. Every year over 9 billion animals are produced for human consumption in the USA and 95 percent are fed GM diets.


Two of the most sensitive toxicological endpoints are effects on weight gain and reproductive performance which are also two of the critical economic considerations for farmers and therefore are carefully watched by them.  Also, when animals are slaughtered for consumption they are routinely examined for any obvious signs of disease.  Despite the very wide spread use of GM feed in such enormous numbers of animals there is no evidence of any adverse effects from the introduction of GM feed around 20 years ago.  No animal toxicity study in a laboratory could ever compete with an ongoing "study" of such magnitude.