The term genetically modified organism (GMO) describes an organism whose genetic material has been altered using genetic engineering. This is different from organisms that have been altered through selective breeding, such in domestic animals, cattle and pigs, as well as most plant species. Genetic engineering is a process in which an organism’s DNA is altered, by mutating, inserting or deleting genetic material, resulting in a transgenic organism.

Genetic engineering has produced transgenic mice, which are used extensively to investigate human disease, such as obesity, diabetes, heart disease and cancer. The drug Humulin, used by millions to manage diabetes, is the product of genetically engineered bacteria. Plants have been genetically engineered for decades, including antibiotic-resistant tobacco plants, and the first genetically modified food for human consumption, tomatoes, which were modified to slow down the ripening process.

The Pros

In crops, transgenic plants are most common, where genes have been inserted into the plant’s cells in effort to provide desirable characteristics, such as resistance to pests or herbicides, or to increase the nutrient content of the plant. Corn, for example, has been modified to increase the lysine content, making it a better source of this key amino acid.

Insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are expressed in corn and other crops, which allows these plants to resist pests, thereby decreasing the need for insecticides. This also, of course, decreases residual insecticides on the plants that we and our horses consume, and decreases the impact on the environment.

Herbicide resistance or tolerance (Ht), such as glycophosphate resistance, allows modified organisms to be treated with herbicides (for example, Roundup®) without negative consequences to the crop. Alfalfa, corn, soybeans and sugar beets are most commonly engineered with Ht. Therefore, there are some important benefits for genetically modified crops.

For GMO alfalfa specifically, farmers can prevent the toxic weed, fiddleneck, from growing with the alfalfa. Fiddleneck is a notable toxic plant for horses and results in liver failure and death. Similarly, corn that can resist pests can also avoid many fungi and mold infections, some of which could produce mycotoxins and cause equine leukoencephalomalacia.

Horse feeds that are not genetically modified include oats, wheat, sorghum and millet.


As of 2013, the United States had 70.1 million hectares planted with GMOs, while Canada had 10.8 million hectares. In the US, 94 per cent of soybeans and 93 per cent of corn are genetically modified. The use of GM crops allows farmers to increase their efficiency of production, which means greater income to them, but also to some degree, better use of land. This latter point is important for other parts of the world, where plants have been genetically engineered to resist heat stress or drought, and, therefore, increases crop yields in impoverished areas. Coupled with increased nutrient content, GM crops are an important introduction into some third world countries.

Nonetheless, there is great controversy regarding the use of GMO in human and horse feeds. While some are concerned about ‘Frankenstein foods,’ there is also worry that since a crop is now resistant to herbicides, more of them could be used. However, horses can actually graze directly on pasture after most herbicide applications, so feeds that have had herbicide application should also be relatively safe. According to Drs. Hart and Singer from Rutgers University, for non-lactating horses, “there are no grazing restrictions for any of the herbicides with the exception of Roundup®.” For Roundup®, horses should avoid a pasture for 14 days if it was a spot treatment, and for 56 days if the entire pasture was treated. This suggests that there might be some concern about Roundup®-treated crops, the most notable of which are soybeans. However, there is no scientific evidence that treated soybeans pose a health threat to horses or humans.

In fact, it is generally recognized by scientific consensus that feeds derived from GM crops have no greater risk to health than the conventional crop. From the Food and Agriculture Organization of the United Nations in 2016: “Currently available transgenic crops and foods derived from them have been judged safe to eat and the methods used to test their safety have been deemed appropriate. These conclusions represent the consensus of the scientific evidence surveyed by the ICSU (2003) and they are consistent with the views of the World Health Organization (WHO, 2002). These foods have been assessed for increased risks to human health by several national regulatory authorities (amoung others Argentina, Brazil, Canada, China, the United Kingdom and the United States) using their national food safety procedures (ICSU). To date, no verifiable untoward toxic or nutritionally deleterious effects resulting from the consumption of foods derived from genetically modified crops have been discovered anywhere in the world (GM Science Review Panel). Many millions of people have consumed foods derived from GM plants – mainly maize, soybean and oilseed rape – without any observed adverse effects (ICSU).”

Feed safety studies using rodents also have revealed no negative effects: “The studies did not show any biologically relevant differences in the parameters tested between control and test animals” (EFSA GMO Panel Working Group on Animal Feeding Trials, Food Chem Toxicol, 2008). Similarly, a study looking at livestock populations before GMOs were commonplace and more recently (when up to 70-90 per cent of feed consumed by animals is genetically modified), found no “unfavorable or perturbed trends in livestock health or productivity.” Likewise, there were “no detectable or reliably quantifiable traces of GE components in milk, meat and eggs following the consumption of GE feed” (Van Eenennaam and Young, Journal of Animal Science, 2014). Therefore, it is also unlikely that GM crops have a negative effect on equine health, though there have not been direct studies to date.

The Cons

It should be noted that before a novel modified crop can be introduced to market it needs to undergo extensive testing. In the US, this is overseen by the United States Department of Agriculture and Environmental Protection Agency regulating crops and the Food and Drug Administration regulating foods for human consumption. In Canada, both Health Canada and the Canadian Food Inspection Agency are responsible for regulating GM plants and crops, for both human and livestock consumption.

Also note that GMO alfalfa seeds (Roundup Ready®Alfalfa) have only been approved in Canada since 2016. This has been causing great controversy because GM alfalfa can cross-pollinate with organic alfalfa and could negatively affect the organic alfalfa market and exports.

There are certainly horse owners who want to avoid any genetically modified organisms in their horse’s feed. Oats are the most common equine feed that are not genetically modified, and this is mainly because they are grown in colder areas that are not as susceptible to pests or weeds. Unfortunately, many horses can’t perform to their expectations on grass and oats alone, and might need some added oil (corn or canola oil are typically from GM plants) or beet pulp for calories, not to mention some soybeans for added protein. Because the majority of crops are now genetically modified, they are cheaper to produce than organic crops, and thus, to purchase, which makes their inclusion into mixed commercial feeds commonplace.

As a result, equine products that are marketed as GMO-free are notoriously expensive. One well-known equine feed company has a GMO-free horse feed that is $6 to $12 more expensive than their non-GMO feeds with similar nutrient profiles. Organic alfalfa pellets are almost three times more expensive than non-organic alfalfa pellets. For many horse owners, this is cost-prohibitive.

Avoiding GMO Feed

If an owner wanted to offer a non-GMO type of diet for their horse, I would suggest offering grass pasture that is only spot-treated for weeds, or feed good quality grass hay. Be sure to test it to make sure the protein content is sufficient, to avoid having to feed soybean meal or alfalfa meal to increase the protein. Oats can be fed to increase calorie intake and vitamins and minerals can be balanced using a commercial vitamin-mineral supplement (the type that is offered at less than 80 grams per day, so it has little to no filler of alfalfa meal or other). Wheat is currently not genetically modified, and could be added (offered in bran form, as whole grain wheat is difficult to chew for horses), to increase both energy density and protein content. However, wheat bran is also extremely high in phosphorus, and the diet should, therefore, be balanced with additional calcium. Barley might also be included in small amounts, though barley starch can be difficult to digest. Sorghum and millet may also be fed to horses, though they are less palatable. Rice and rice bran are another good option for equine feed. If a horse had higher needs (such as growing horses, breeding animals and top athletes), it might be recommended to invest in non-GMO soybeans and alfalfa to increase the nutrient density of the diet.

Alternatively, a quick search on the internet will find you some GMO-free commercial horse feeds. I would recommend selecting a commercial feed from a well-known and respected company to ensure that they have Ph.D. equine nutritionists helping to formulate the feed. My search found a few products from smaller organizations and feed mills that might need a little more scrutiny, especially to justify their higher prices.

Personally, I am not concerned about the actual practice of genetic modification in crops, and do believe it can be helpful to increase the efficiency of land use, nutrition of the product, and, in some respects, could be better for the environment (i.e. decreasing pesticide use). I do worry about potentially increased used of herbicides, though perhaps less from a food safety issue, and more as an environmental concern. Given the choice, I typically opt for organic foods myself, and would likely do the same for my own horses, if it were a viable option. This is certainly a niche market that I expect will increase in the coming years.