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Abstract

A significant number of genetically modified (GM) crops have been approved to enter human food and animal feed since 1996, including crops containing several GM genes ‘stacked’ into the one plant. We randomised and fed isowean pigs (N=168) either a mixed GM soy and GM corn (maize) diet (N=84) or an equivalent non-GM diet (N=84) in a long- term toxicology study of 22.7 weeks (the normal lifespan of a commercial pig from weaning to slaughter) . Equal numbers of male and female pigs were present in each group. The GM corn contained double and triple-stacked varieties. Feed intake, weight gain, mortality and blood biochemistry were measured. Organ weights and pathology were determined post-mortem. There were no differences between pigs fed the GM and non-GM diets for feed intake, weight gain, mortality, and routine blood biochemistry measurements. The GM diet was associated with gastric and uterine differences in pigs. GM-fed pigs had uteri that were 25% heavier than non-GM fed pigs (p=0.025). GM-fed pigs had a higher rate of severe stomach inflammation with a rate of 32% of GM-fed pigs compared to 12% of non-GM-fed pigs ( p=0.004). The severe stomach inflammation was worse in GM-fed males compared to non-GM fed males by a factor of 4.0 (p=0.041), and GM-fed females compared to non-GM fed females by a factor of 2.2 (p=0.034).

Introduction

Genetically modified (GM) crops have entered human food and animal feed in increasing amounts since they were commercially released into fields in the USA in 1996 (USDA, 2011). The main traits in GM crops to date have been to express proteins for herbicide tolerance (Ht) and insect resistance (Carman, 2004; USDA, 2011). Herbicide tolerant crops are engineered to produce one or more proteins that allow the crop to survive being sprayed with a given herbicide. Insect resistant crops are usually engineered to produce one or more insecticidal proteins that are toxic to target insects. The latter proteins are usually Bt proteins, so named because they are structurally similar to naturally-occurring Cry proteins from a soil bacterium, Bacillus thuringiensis (ANZFA, NDb). Hence these crops are also called Bt crops.

Of the GM crops planted in the USA, herbicide-tolerant GM soy has been widely adopted and now constitutes 94% of the soy planted in the USA (USDA, 2011). GM corn varieties have also been widely adopted in the USA (USDA, 2011). They usually contain Ht or Bt traits, or a ‘stacked’ combination of them (Pioneer Hi-Bred, 2012).

Prior to the release of a new GM crop into the food supply, the developer provides food regulators in many countries with studies it has done on the crop. These studies often include animal feeding studies, even though some regulators, such as Australia’s, do not require them (FSANZ, ND; Carman, 2004), while the USA has a voluntary system. Many food regulators do not require any studies to be done on crops containing several “stacked” genes if all the genes in the stack have previously been individually approved for use in the same kind of plant (EFSA, 2010; FSANZ, 2010). Consequently, safety studies on stacked crops are less frequent, even though an analysis of official data (USDA, 2011) indicates that over 37% of GM corn varieties currently planted in the USA are stacked with both Ht and Bt traits.

There have been a number of reviews of the published literature on the safety of GM crops. For example, Flachowsky et al. (2005) and Preston (2005) both conducted reviews and both concluded that GM crops were safe for animals and people to eat. However, many of the feeding studies reviewed used non-mammals (e.g. birds, fish) or animals were fed the crop in a form that humans do not eat (e.g. silage) or only animal production outcomes were measured such as body weight, carcass weight, breast meat yield or milk production, which may not be indicative of potential human health outcomes (Carman, 2004). Only a small proportion of published animal feeding studies have been longer-term toxicological studies where a GM crop was fed to animals that are physiologically comparable to humans, and organs, blood and tissue samples were taken from the animals and examined to assess if the crop caused any adverse effects.