Thursday, July 4, 2013

The story about GMO-fed pigs with stomach ailments? Not exactly what they're claiming.

Lots has been made of a report that GMO feed causes stomach inflammation in pigs.

As usual, popular accounts of the science don’t tell the whole story. If you read the study, and we did, you’ll find it doesn’t say exactly what they’re saying it says.

The study, published in the Journal of Organic Systems, is entitled “A long-term toxicology study on pigs fed a combined genetically modified (GM) soy and GM maize diet.” Researcher authors are American and Australian, and include organic farming advocates, although they assert that they have no conflicts. The journal, which is Australian, is supported in part by the Organic Federation of Australia, the Australian government, and a New Zealand sustainable agriculture organization, CSAFE.

They separated 168 pigs into two equal groups, feeding some organic corn and soy, and others corn and soy that had been genetically modified for insect and/or herbicide resistance. (A few young pigs in both groups died during the 23-week trial, at rates that the authors say are standard for commercial hog production.)

The study admits that the GM-fed pigs were fed somewhat moldy feed, while the non-GM pigs received feed with less significant levels of mold. “Mycotoxin analyses (Midwest Laboratories Inc, Omaha, Nebraska, US) showed 2.08 ppb total aflatoxins and 3.0 ppm total fumonisins in a pooled sample of the GM feed and no aflatoxins and 1.2 ppm total fumonisins in a pooled sample of the non-GM feed.”

But the authors insist that this had no impact on their results: “The concentration of mycotoxins in the feed was insignificant.”

In virtually every test the researchers recount, there was no statistical difference between the two groups of pigs. They were inspected and blood was taken when they were alive, and they were autopsied once they were slaughtered.

“There were no differences between pigs fed the GM and non-GM diets for feed intake, weight gain, mortality, and routine blood biochemistry measurements,” they wrote.

The only significant difference was stomach inflammation, and even that is not nearly as clear as you’d expect, given the way the popular press has told the story.

Most of the pigs in both groups had some level of stomach inflammation, although it was not equally distributed. And in fact, 11 percent of GM-fed pigs had no stomach inflammation whatsoever, while only 5 percent of non-GM-fed pigs had no stomach inflammation at all.

Of 73 non-GM pigs, 69 had some level of stomach inflation. Of 72 GM-fed pigs, 64 had some level of stomach inflammation. The difference: in the pigs with severe inflammation of the stomachs, more tended to be GM-fed.

If you’re appalled at the presence of any stomach inflammation in pigs, know that it’s a common occurrence due to feed preparation: “The pig industry uses finely-ground feed to maximise feed efficiency which can increase inflammation and ulceration of the stomach,” the authors note.

The researchers wisely say—as researchers commonly do—that their results demand more study. What are the odds that the results would be different if you did the same study again?

But just to be clear, while their results show statistically that severe inflammation of the stomach was more common in the GM-fed pigs, it is also true that inflammation as a whole was more common in the non-GM pigs.

And it would be technically accurate, though also misleading, to write a headline that said: “Stomach inflammation in pigs higher when fed organic diet.”

© Jan TenBruggencate 2013

1 comment:

Anonymous said...

"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)"