The Breakdown of "Substantially Similar"

via wikipedia

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).

So runs the abstract of the new paper A long-term toxicology study on pigs fed a combined genetically modified (GM) soy and GM maize diet published in the Journal of Organic Systems (JOS) Vol.8 No.1 (2013).
Dr. Carman, in her clear English explanation of the study (pdf), says:

Some of the investigators had previously seen a reduced ability to conceive and higher rates of miscarriage in piggeries where sows were fed a GM diet, and a reduction in the number of piglets born if boars were used for conception rather than artificial insemination. Artificial insemination guarantees the presence of a certain number of viable sperm. Because male pigs were neutered at 3 days of age in order to provide meat free of boar-taint, we were only able to look at the female reproductive system in these pigs. We found that, on average, the weight of the uterus of pigs fed the GM diet, as a proportion of the weight of the pig, was 25% higher than the control pigs. We found that this biologically significant finding was also statistically significant. We list some of the pathologies that could be occurring in these uteri in the paper.

Some of the investigators had also previously seen higher rates of intestinal problems in pigs fed a GM diet, including inflammation of the stomach and small intestine, stomach ulcers, a thinning of intestinal walls and an increase in haemorrhagic bowel disease, where a pig can rapidly “bleed-out” from their bowel and die. We weren't able to look inside the intestines, due to the amount of food in them, but we were able to look inside the stomach. We found that the level of severe inflammation in stomachs was markedly higher in pigs fed the GM diet. Pigs on the GM diet were 2.6 times more likely to get severe stomach inflammation than control pigs. Males were more strongly affected. While female pigs were 2.2 times more likely to get severe stomach inflammation when on the GM diet, males were 4 times more likely. These findings are both biologically significant and statistically significant.

We found that these key findings were not reflected in the standard biochemistry tests that are done in GM feeding studies, probably because standard biochemistry tests provide a poor measure of inflammation and matters associated with uterus size. We did however find a marginally significant change on a measure of liver health in the blood of GM-fed pigs.

GMO seeds were allowed into the food system without extensive or multi-generational testing because they were "substantially similar" to foods already in use.  It's starting to become scientifically apparent that this was a mistake.