Just when you thought the market for controversy over genetically modified organisms (GMOs) was completely saturated, a new study published in the Journal of Organic Systems finds that pigs raised on a mixed diet of GM corn and GM soy had higher rates of intestinal problems, “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.” Both male and female pigs reared on the GM diet were more likely to have severe stomach inflammation, at a rate of four times and 2.2 times the control group, respectively. There were also reproductive effects: the uteri of female pigs raised on GM feed were 25 percent larger (in proportion to body size) than those of control sows. (All male pigs were neutered, so scientists were unable to study any effects on the male reproductive systems.)

The study confirms anecdotal evidence from hog farmers who’ve reported reproductive and digestive problems in pigs raised on GM feed. Those who were following this sort of news in 2011 will remember an open letter to the USDA from Dr. M. Huber, a professor at Purdue University, about an unknown organism in Roundup Ready crops causing miscarriages in farm animals.

A common complaint from critics of GM technology – often painted as “anti-science” by GM proponents – is that they’ve been inadequately studied. (Don’t think about that for too long – your first instinct is correct, it doesn’t make sense.) The European Union has long based its regulatory framework (and resultant slow adoption of GMOs) on the precautionary principle. And in fact, according to this study, most of the research on the health impacts of GMOs has either been short term (less than 90 days), performed on non-mammals or failed to examine multiple GM traits concurrently, despite that many new GM crops “stack” traits, and that many diets – of both animals and humans – include multiple types of GMOs.

The scientists behind the study report having chosen pigs as their subject for the similarity between their digestive systems and those of humans, and the mixed GM diet for its similarity to the real-life diets of both swine and humans, so this is really damning stuff. They also describe their findings as conservative, noting that even the control group is likely to have been exposed to GMOs in indirect ways they couldn’t avoid, such as trace amounts of GMOs in non-GM feed, and parents fed GM diets.

As one might expect, the scientists conclude their report with a call for more testing, particularly of whether the findings also apply to humans. Scientists at the Consumers Union go one further, saying that concerns raised by the study further underscore the need to label GMOs.

Will the government listen? Time will tell. It’s also  hard to predict the potential impact of this study on the US pork market – or on the prices of corn and soy. As we saw recently when Japan and South Korea canceled orders for US-produced wheat after the discovery of unapproved GM wheat in Oregon, not all countries take a laissez-faire approach to GMOs. And what about that merger/takeover of Smithfield Foods by Chinese-held Shuanghui, rumored to have been spurred in part by friction over the livestock drug ractopamine? For that matter, will American hog farmers – seeking rightly to avoid sickening their own hogs – seek non-GM feed from other countries?