Poor feed choice invalidates GMO feeding study

posted in: Science | 27
Something smells around here… and it’s not the pigs! Pigs by Andreas Klinke Johannsen via Flickr.

The new pig feeding study has really made a splash in the media, with uncritical journalists taking it at face value. The paper is titled: A long-term toxicology study on pigs fed a combined genetically modified (GM) soy and GM maize diet by Carman et al, if you’d like to read it.

Happily, many highly qualified bloggers have provided thoughtful rebuttals on various aspects of the study. I’d like to present my own review, as a crop scientist (specifically, a PhD in genetics, focusing on plants, with a minor in sustainable agriculture). I’ll examine the sources of the GM and non-GM grain used in the study and show why their choices invalidate the entire study, even before you consider the poor use of statistics and issues with animal husbandry (read: animal welfare).

First, a quick clarification. The authors state in the introduction that FDA’s food safety consultation process is voluntary. While this is technically true, it is also true that it is against US law to put a new food additive (such as  Bt) on the market without consultation. The FDA states: “Food and food ingredients derived from GE plants must adhere to the same safety requirements under the Federal Food, Drug, and Cosmetic (FD&C) Act that apply to food and food ingredients derived from traditionally bred plants.” All of the genetically engineered crops available on the market have gone through the FDA’s extensive consultation procedure.

The authors aimed to do a real world study, with pig feed that can be found in real life. It intuitively seems right to just go get some grain from some farms. After all, that is what pigs eat, right? Unfortunately, it’s just not that simple.

The study aims to test the difference between GM crops and non-GM crops. To hone in on any differences that may be caused by the GM traits, they would have to use feed with one or more GM traits and feed that doesn’t have the GM traits but that is otherwise as similar as possible. If the feeds aren’t very similar, then we can’t know if any differences in the animals is due to the GM traits or due to something else.

What varieties and genes were tested?

While it may not be as easy to see the differences between varieties of corn or soybeans, they are as diverse as these tomatoes. Tomato heaven by Mia Holte via Flickr.

As we can experience size, shape, smell, taste, color, and other differences between the varieties of tomatoes, peppers, citrus, and other produce we find in the grocery store, we can also expect differences between varieties of corn and between varieties of soy – the differences may not be as visible, but they are there!

While they tell us the varieties of GM corn and soy, the authors do not tell us what varieties of corn and soy were used for the non-GM feed, which makes it impossible for us to know if they were similar to or different from the varieties in the GM feed.

There were 4 GM varieties of corn used in the study, which had 3 genes between them: NK603, MON863 and MON810 (links go to the completed FDA consultations). DNA analysis confirmed these genes in the corn. The soybean variety is unknown, and the exact gene in the soybeans is unknown, but DNA analysis found genes for the protein that confers glyphosate tolerance.

They also found that the non-GM corn had a median of 0.4% GM content and the non-GM soy contained a median of 1.6% GM content. Note that instead of reporting the average GM content, they reported the median. The median is the midpoint of all of the measurements if they are listed in order. It is often used for data that is skewed high or low. Does this mean that the results here were skewed? The data is not provided, so we just don’t know. It’s just weird. I’d expected a mean with standard deviation.

Genetic ID, a “GMO identification” company, performed the DNA testing. This company is certified for “biological testing” and they state that they use quality controls. However, we should keep in mind that  the company and its founder have connections to Jeffery Smith, well known anti-GMO activist, as well as the Non-GMO Project. They arguably have a financial benefit in convincing people GMOs are dangerous. This is not the only conflict of interest we have with this paper, but I’ll let other bloggers delve into that. Just for anyone who’s still reading, I did want to note that I am not being compensated for writing this, and I do not have any financial connection to the biotech industry.

Why does the variety matter?

The authors argue that there are multiple parents for each variety of GM corn and soy, so choosing a non-GM variety that is genetically the same would be very difficult. They have a good point, but there are other, relatively easy, ways to minimize differences between the two feeds that were not used in this study. For example, the environment in which plants are grown can have a large effect on the proteins and other compounds produced by a plant. So, it would be best to grow the GM and non-GM crops in as close to identical conditions as possible, with the same soil, same weather, and same growing practices. It would also be helpful if they had the same treatment with regard to irrigation, fertilizers, insecticides, herbicides, and any other inputs. Since we don’t know anything about the farms the GM and non-GM crops were grown on, we don’t know how similar or different they might have been.

Now, I have seen some people argue that the researchers couldn’t control the growing conditions of the grain because the seed companies prevent research by not providing research licenses. While this was true in the past, it is not true today. These researchers could easily have partnered with researchers at any of 100 universities in the US that have blanket Academic Research Licenses to do research with Monsanto seed, including “studies related to end-use such as animal feeding”.  The researchers don’t even have to contact the company or sign a separate contract.

As the authors mention, science agencies all over the world have determined that there are no significant differences between GM crops and their non-GM counterparts. We can put this another way and say that the GM varieties fall within the natural variation expected for that type of crop. However, natural variation is huge. For example, the carbohydrates in soybeans can vary from 26-50% of dry weight! Soybean isoflavones can vary from 700 mg/kg of soybeans to almost 10,000 mg/kg! The isoflavone content is particularly interesting because these compounds can mimic estrogen in mammals, and can even cause changes in reproductive tissues when eaten at high doses. Isoflavone content can be affected by how the plants were grown, highlighting how important it is to have similar growing conditions for the GM and non-GM crops. The OECD has some great summary documents about nutrient composition of crops that show varietal differences within each crop.

What went into the feed?

Table 1 shows how they made the feed. They added off the shelf nutrients plus the GM or non-GM grains, which typical for feed. This is useful information, but the table does not address any of the possible compositional differences between the GM and non-GM grains themselves, including macro-nutrients, micro-nutrients, anti-nutrients, pesticide residues, isoflavones, and so on. The researchers have no way of knowing whether or not the GM and non-GM grains are comparable unless they do some sort of tests on the grain. Given the huge amount of variability among corn and soy varieties, such tests are essential for this sort of study.

By not controlling the variety or the environment, the researchers had no idea what the composition of the GM and non-GM grain might be.  They didn’t do any tests to see what variation might be there, even though variation in feed can cause variation in health in the animals that eat the grain, totally unrelated to GM traits.

Table 1 does show the % of protein in each of the 6 sub-diets, which presumably was measured for each diet after they had been mixed (this was not explained), but there are a lot of things in feed besides protein that can have a measurable effect on pigs. In the US (and presumably elsewhere), granaries test the grain for micro- and macro-nutrient content as well as for various naturally occurring toxins. Then, they blend different batches of grain to get just the nutrient content they want (and reject any grain that does not meet strict parameters for nutrition and safety). The authors don’t mention any kind of testing or blending to match the GM and non-GM feeds for nutrients. What if the non-GM soy happened to be super high in carbs but the GM soy happened to be low in carbs? What if one was really high or really low in isoflavones?

On real world pig farms, the feed is changed depending on the needs of the animals as they grow. The authors changed the feed in this way, which is great. They added extra vitamins, which is normal for pig feed. However, they didn’t test the nutrients and anti-nutrients in the corn and soy going into the feed.

The authors tested for mycotoxins, which is important for the safety of the animals. Mycotoxins are toxic substances that can be produced by certain types of fungus that can grow on corn. The results are strange, though. Previous studies have shown that Bt corn has lower levels of mycotoxins. The reason is likely due to the fact that Bt corn has less insect damage, and fungus often enters corn kernels through the holes made by insect bite marks. Having higher mycotoxins in the GM feed may indicate that it has been in storage longer, perhaps too long, which could result in other compositional changes. We don’t know if such differences were there, or if so what they might be, because this was not tested.


The authors had some good ideas for their study, including using a relatively large number of pigs and keeping the experiment going for the normal lifespan of the pigs. However, as a crop scientist, I see too many problems with the sources of the GM and non-GM crops in the feed for me to say that the results are reliable. This is a shame, because a lot of pigs lost their lives here. I don’t even think the meat from the animals could be eaten since so many of them were sick with pneumonia and who knows what else. Mortalities were incredibly high (13% for non-GM and 14% for GM), which is not within expected rates for US commercial piggeries (which are more like 5% or less EDIT: See comments for discussion of mortality rates), regardless of what the authors claim (without providing a reference).

We have to wonder what kind of animal husbandry issues were happening on the farm for so many animals to be so sick – this is not normal.

I really wish that researchers like this would take the time to double-check their methods before doing the experiment. If they’d talked with a crop scientist like me, they would have learned that the potential for compositional differences was too high, and I could have recommended some ways to minimize those differences. It might take a little more time and money, but isn’t it worth it to have good results, especially when so many lives are used in the testing?

Ideally, a feeding study like this would have controlled growing environments, genetic isolines, and testing of the grain. Some researchers use controlled environments and isolines, then only do a few composition tests to check for equivalence of nutrients, etc in the grain. If isolines are not available, one could do the study with a suite of comparator varieties instead of just one, then see if results of the GM are within the range of the non-GM varieties.  The researchers did none of these.

The feed just was not similar enough to tell if any differences found in the animals was due to GM or something else entirely. This one flaw invalidates the entire study.

Judy A. Carman, et al. (2013). A long-term toxicology study on pigs fed a combined genetically modified (GM) soy and GM maize diet, Journal of Organic Systems, 8 (1) 38-54.

Follow Anastasia Bodnar:
Anastasia is Policy Director of Biology Fortified, Inc. and the Co-Executive Editor of the Biofortified Blog. She has a PhD in genetics with a minor in sustainable agriculture from Iowa State University. Her favorite produce is artichokes!
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