Opponents of genetically engineered (GE) crops routinely argue there is a lack of evidence regarding their safety for use in food or animal feed. Science, they claim, has not “proven” that GE crops are safe, therefore they must be dangerous, they say as they call for restrictions and warning labels.

Setting aside the issue of “proof,” we know that in most types of quantitative research, big numbers, big sample size and big data sets replicated over time translate to reliable, valid conclusions. So in regard to the safety of GE crops in livestock feed, how does 30 years of data on 100 billion animals sound?

That enormous number comes from a new scientific review conducted by University of California – Davis animal scientist Alison Van Eenennaam, Cooperative Extension Specialist in Animal Biotechnology in the Department of Animal Science at the University of California, Davis, and research assistant Amy Young. The article, titled "Prevalence and impacts of genetically engineered feedstuffs on livestock populations," is published in the latest issue of the Journal of Animal Science, and is available for public access.

In preparing the report, the researchers compiled livestock-feeding data from 1983, which was 13 years before GE crops were introduced, through 2011, when GE feed use exceeded 90 percent. In 2013, GE varieties were planted on more than 95 percent of the sugar beet crop, 93 percent of soy, and 90 percent of all cotton and corn acres in the United States, according to the USDA.

Due to widespread adoption of GE crops, the researchers note, large numbers of livestock in many countries have been consuming GE feed for more than 15 years. Hence, a very large and powerful set of GE-fed target animal data has been quietly amassing in public databases. U.S agriculture feeds billions of food-producing animals each year, with annual broiler numbers alone exceeding the current size of the global human population.

Based on the increase in GE adoption rates between 2000 and 2013, the researchers predicted that the vast majority of conventionally raised livestock in the United States consumed feed derived from GE crops over the past decade. Cumulatively, they note, this amounts to over 100 billion animals consuming some level of GE feed between 2000 and 2011.

It stands to reason that if GE feeds were harmful to animals, those effects would turn up in their health and/or performance. And over the past 30 years, researchers have conducted hundreds of controlled studies measuring health and performance of cattle, hogs, poultry, fish and other species.

Van Eenennaam and Young conducted an extensive review of available data from those studies, looking at trends in overall animal performance, health indicators such as somatic-cell counts in dairy cattle, feed-conversion ratios and condemnation rates at slaughter. Across their enormous set of animal observations, they found no evidence of declines in animal health or performance or any change in the overall trends since the introduction of GE crops. In fact, measures such as milk yield, somatic-cell counts, carcass weights of cattle, hogs and broilers and feed-per-gain ratios in broilers all have improved over the study period while mortality rates and carcass condemnations have improved or remained stable.

“There was no indication of worsening animal health after the introduction of GE feed, and productivity improvements continued in the same direction and at similar rates as those that were observed before the introduction of GE crop varieties in 1996,” the researchers note.

The review also examines the composition of products derived from animals fed diets containing GE feeds. “No study has revealed any differences in the nutritional profile of animal products derived from GE-fed animals,” state the authors.

“I believe that information in this peer-reviewed article is essential for open-minded discussions of GE feeds and foods,” writes Gregory S. Lewis, PhD, Editor-in-Chief of the Journal of Animal Science in an editor’s note, “and we have made this information freely available to the public.”

View the full article from the Journal of Animal Science