Feeding GMO Crops to Livestock

by Alison L. Van Eenennaam, Ph.D., and Amy E. Young, Department of Animal Science, University of California, Davis


Everyone has seen the acronym GMO, whether in a press article or a piece of legislation. GMO stands for “genetically modified organism.”  It’s also known as transgenic, bioengineered, biotech, and “Frankenfood.” While these words are often used interchangeably, the term “GMO” is ill-defined, since most domesticated animals and crops are “genetically modified” to some extent due to selective breeding by humans. The term “genetically engineered” (GE), however, specifically refers to the manipulation of an organism’s genes using modern molecular biology and accurately describes the food and feed that is at the forefront of the global discussion. It is important to remember that GE is a breeding method, not a company, application or production system. It is simply one of the methods that can be used to develop improved crop varieties.

Genetically engineered crops have been widely adopted since their introduction in 1996, with more than 95 percent of sugar beet, 94 percent of soy and 96 percent of cotton and corn acreage planted with GE varieties in the U.S. in 2014. As these crops are major components of feedstuffs, livestock populations have been the major consumers of GE crops, and multiple generations of food-producing animals have been consuming 70-90 percent of GE crop biomass for almost 20 years. Science has shown that GE crops do not differ from non-GE crops in terms of composition, and no significant differences in health or performance have been detected in animals that consume GE feed. Additionally, no traces of GE material (rDNA or protein) have been detected in meat, milk, or eggs from those animals. 


Performance Trends in U.S. Livestock Populations

Sensational stories have been reported in the media based on a handful of highly controversial studies that claim to show deleterious health effects in a small number of animals that have consumed GE feed. Despite the fact that these studies have been widely criticized for experimental design, small sample sizes and methodological flaws, they continue to be used by some groups to suggest that GE crops are harmful to animal health. These claims are contradicted by the hundreds of carefully-conducted animal feeding studies that have been performed by independent scientists throughout the world, a list of which is maintained and made freely accessible online by the Federation of Animal Science Societies (FASS) (http://www.fass.org/page.asp?pageID=52).

Numerous recent studies with a variety of food-producing animals fed with the current generation of GE crops consistently show no difference in performance and health in comparison to animals fed non-GE feeds. Most of those datasets are reflective of a controlled experimental environment, but what about out in production agriculture? Keeping in mind the significant increase in GE crop adoption rates between 2000 and 2013, and the fact that a very small proportion of the commercial livestock population (< 5 percent in 2011) was raised for certified National Organic Program (NOP) markets, it can be estimated that more than 100 billion animals in the U.S. consumed some level of GE feed in their diets between 2000 and 2011. If GE feed had detrimental effects on animal health or performance, it would have been reflected as a negative trend in the health of these commercial livestock populations during the past decade.

In a 2014 review in the Journal of Animal Science (Van Eenennaam and Young, 2014), an analysis of publicly available data for health and production parameters across commercial poultry, dairy, beef and hogs showed no significant deleterious health or performance trends in any of these industries. Carcass condemnation rates were examined as an important production parameter in beef cattle over this time period. The data show that a total of 0.47 percent of carcasses inspected at USDA-inspected slaughter facilities from 2003 through 2007 were condemned. Cattle fed or finished in feedyards, and therefore typically fed diets rich in corn and soy (the vast majority of which are of GE varieties) before slaughter, made up the majority (82 percent) of cattle at harvest but were the minority (12 percent) of cattle condemned. The condemnation rate for non-fed cattle (typically old cows) was higher than that for fed cattle, but the 2007 rate of 2.49 percent was similar to the reported rate in 1994, before the introduction of GE crops, of 2.6 percent.

These field data, representing billions of observations, did not show any unfavorable trends across any of these animal production industries after the introduction, and during the widespread adoption, of GE feed. In fact, available health indicators actually improved over time and productivity continued to improve, due likely to improved management and genetic selection, and at similar rates as observed in 1996 before the introduction of GE crop varieties.

GE Animal Feed in Global Trading Markets

In a brief released by the International Service for the Acquisition of Agri-Biotech Applications (ISAAA) in January 2015, it was reported that in 2014 a record 448 million acres of biotech crops were grown globally. This is an increase of 15 million acres since 2013. The U.S. remains the leader in biotech crop production, with 181 million acres, up 7 million acres since 2013, followed by Brazil (104 million acres) and Argentina (60 million acres). Herbicide-tolerant soybean and maize events continue to have the most approvals worldwide.

Soybeans and corn, the two major components in commercial animal feed, make up two-thirds of the global grain trade. The U.S., Brazil and Argentina, the three countries with the highest levels of biotech crop production, are also the main countries that grow and export these crops.  Estimates report that 4 percent of global soybean trade and 7 percent of global corn trade are required to be certified non-GE. For countries that rely on imported feed, sourcing non-GE products is becoming complicated due to the high GE adoption rate in the major feed exporting countries. Some countries that have previously committed to sourcing only non-GE feed for certain sectors have recently abandoned those plans.

Further complicating matters, worldwide grain commerce has experienced trade disruptions due to asynchronous approvals. The amount of time needed to review and approve new GE crops varies considerably across different countries; leading to a situation in which GE crops may be cultivated and marketed in some countries but remain under evaluation in others.  Significant trade disruptions have already occurred, especially when countries use a “zero tolerance” policy for unapproved events, meaning that even minute traces of unapproved GE crops are illegal and must be withdrawn from the market. In the future, it is likely that trade between countries with asynchronous approvals will be increasingly problematic as countries with zero tolerance policies will be perceived as risky due to the high costs associated with finding even minute traces of unapproved GE material. Non-GE feed for animals in the U.S. is more expensive and the supply is increasingly come from other countries such as China and India.

Genetically Engineered DNA in Animal Products and the Labeling Issue

It has been well-established that it is not possible to detect differences in the nutritional profiles of milk, meat and eggs from animals fed GE feed versus animals that have consumed non-GE feed. No reliable traces of GE DNA or protein have been detected in products from GE-fed animals. Livestock and humans regularly digest DNA and protein without any adverse consequences, and DNA from GE crops is chemically the same as DNA from non-GE crops and broken down no differently during the process of digestion. A freely available publication from the Council for Agricultural Science and Technology (CAST, 2006) provides details on the safety of products from animals fed GE crops. Currently, only a small number of livestock producers feed non-GE diets to their animals, meaning that well over 95 percent of the milk, meat and eggs on the US market today come from animals that have consumed GE feed.

Since there are no detectable traces of GE material, labeling of such products would rely on documenting the absence of GE crops all the way through the production chain, a costly and time-consuming proposition for producers and importers. There would be no way to test finished products to guarantee the complete absence of products from GE-fed animals. A 2014 study from Cornell University estimated that the costs to implement labeling based on maintaining product identity, as well as the costs of labeling itself, for a family of four for a year are  $348-401 in California, $360-490 in Washington state and $500 in New York. Consumer surveys taken in Europe show that labeled products are likely to be dropped, actually resulting in fewer options on supermarket shelves. In the United States, voluntary, process-based labels, such as Organic and the Non-GMO Project verify that GE crops were not used in the production process and are available for those consumers that choose to purchase such products.


Overall, there have been substantial benefits from the adoption of GE crops in the US and worldwide. These include economic and environmental benefits such as lower production costs, fewer pest problems, reduced use of pesticides, and better yields. The overwhelming consensus of data shows that GE feed is safe for animal consumption and does not result in animal products that are compositionally different from those produced by animals that were fed feed derived from conventional crop varieties. Field data sets representing billions of observations are in agreement with the many controlled animal feeding studies that have reported no detrimental health effects in animals fed GE feed and revealed no deleterious trends in U.S. livestock health and productivity data since the introduction of GE crops. 

Additional Resources

Tags: Beef Issues Quarterly, Spring 2016, Trends Analyses

March 30, 2016