On the Subject of Soy | BioStar US

On the Subject of Soy…

Soy is one of the most common ingredients in equine feed, and is also found in various equine supplements and oil blends. It’s a relatively new addition to the equine diet. BioStar does not use soy or soy products, and here are some reasons why.

A brief history of soybeans in western countries
In the 1800s and early 1900s, soy was not on the equine menu in the US and Europe.  Although soy sauce was imported to Europe as a condiment in the 1850s, soy plants were only grown in botanical gardens as ornamental plants, not for food.

Following the Russo-Japanese War (1904-1905) England began importing soybeans to crush for oil as a replacement for cottonseed and linseed, which were in short supply.  Soybean oil was for industrial use rather than for food.

Soybean farming took off in the US during World War II as China, the major supplier at the time, was facing internal revolution. The demand for lubricants, plastics and other products during wartime made soybean production a necessity.

In the post-war period, economic prosperity rose and the demand for meat increased. US livestock producers found that soybean meal was the preferred source of protein at a low cost.

In the 1970s, US Secretary of Agriculture Earl Butz began implementing a hyper-efficient centralized food system that could profitably and cheaply “feed the world” by planting millions of acres of corn and soy. As one editorial put it, Butz, a Nixon appointee, “was the patron saint of the Fast Food Nation.”

Soybean oil is used for cooking French fries and fried chicken, breads contain soybean oil, tortilla and taco shells contain soybean oil, as well as processed American cheese, salad dressings, Twinkie filling and frostings.  On labels, you will find soy referred to as hydrolyzed vegetable protein, textured vegetable protein, hydrolyzed plant protein, isolated vegetable protein, and vegetable broth.  “Natural flavors” also indicates soy.

Farmers in the post-war boom remembered the lessons of the dust bowl, and knew that high-production agriculture could devastate productivity of the land.  To make the shift more palatable to Midwestern farmers, Butz’s plan was to sell more corn and soy overseas, and to capture new markets in the US. One of those markets ended up being horse feed, and later came dog food.

In order to face the challenges of “feeding the world” with essentially two crops—corn and soy—more chemical fertilizers were needed, along with more herbicides and pesticides, and by the 1990s, genetically modified organisms.

Today the US leads the world in soy production: 70.9 million hectares in cultivation, with Brazil a distant second at 44.2 million hectares.  Around 70% of the soy grown worldwide goes to livestock feed.

What does soy provide to horses?
Feed companies recommend soy as a good protein source for horses, as soy provides important essential amino acids including lysine. Nutritionists recommend that soy in horse feeds and supplements be processed (cooked, micronized, flaked, extruded, etc.) and not fed raw. The processing is to deactivate an enzyme in soy that is a protease trypsin inhibitor. Trypsin is an enzyme that’s important for the digestion of proteins.

Soy can provide a range of nutritional values depending on processing: 30-48% protein and 10-20% fat.

The various forms of soy in feeds and supplements include: soybean meal (a byproduct of soybean oil extraction), soybean hulls, soybean flour, roasted soybeans, soybean flakes, extruded soybeans, soybean oil and vegetable oil.

Soy is a primary source of omega-6 fatty acids.  While these fatty acids are important for horses, too much omega-6 in the body can result in excessive inflammation.  The ratio of omega-3 to omega-6 in soy is almost 1:8.  Compare that to flax, which is 4:1.  Horses that don’t have access to fresh forage 7-8 hours a day may not be getting enough omega-3 to counterbalance the low omega-3 content of hay and the high omega-6 content of commercial feeds.

Soybean oils
Soybean oil and vegetable oil (a blend of corn and soy) can be processed two ways: expeller-pressed, or by solvent extraction.  Expeller pressing (also known as mechanical pressing) is how oil extraction was done for centuries.  An expeller is just a big screw that’s tightened until it crushes the nut or seed, causing the oil to run.  Mechanical pressing can create high temperatures, particularly with automatic machinery, which can denature the oil.  Also, expeller-pressing can only yield 65-70% of the oil in the seed.

Solvent extraction is much more efficient, recovering 99% of the oil, but the process uses hexane—a neurotoxic petrochemical solvent listed as a hazardous air pollutant by the EPA.  Once the oil has been solvent extracted, the mixture is heated to a very high temperature to burn off the hexane.  This denatures the oil and destroys nutrients.  The FDA does not require food manufacturers to test for hexane residue.  However, tests conducted by the Cornucopia Institute in 2009 did find hexane residue in soybean oil.

The term “cold-pressed” implies a low-temperature processing.  But this term is not regulated in the US, as it is by the EU. In the EU, cold-pressed is defined by a specific temperature range, and any oil labeled as such cannot exceed a maximum temperature of about 90°F during processing.  In the US, “cold-pressed” can mean any temperature under 400°F.

Serious considerations
There are some important things to address regarding soy as a food for horses.  Some horses are sensitive to soy, which can manifest as behavioral issues.  For other horses soy acts as an allergen, causing food intolerance.

For some mares, the phytoestrogens in soy create an overload that can present itself in more “mareish” behavior, irregular cycling, and a cranky or spooky attitude under saddle.  Soy can also be a contributor to infertility problems and endocrine dysfunction in stallions and mares.

There is evidence that feeding soy may contribute to digestive problems including bloating and gas.  This can be due to the oligosaccharides in soy.  “Oligo” means few and saccharides are sugars.  The specific oligosaccharides in soy are raffinose and stachyose.  These oligosaccharides require an enzyme called alpha-galactosidase.  Humans, horses and dogs may not produce enough of this enzyme to digest the oligosaccharides, leading to gas and or inflammation in the hindgut.

Genetically modified soy and the herbicide Roundup
Then there’s the issue of how soy is cultivated; 99% of the soy used in horse feeds and supplements is genetically modified. Genetically modified soy has been developed into glyphosate-tolerant soy, allowing farmers to use more glyphosate (Roundup) on their fields.  A study published in Food Chemistry (volume 153, June 2014, pages 207-215) found that “glyphosate tolerant genetically modified soybeans contain high residues of glyphosate and AMPA” (Aminomethylphosphonic acid is one of the primary metabolites of glyphosate.)

Health concerns with Roundup
Studies conducted in the EU and Russia investigated the effects of glyphosate on the overall activity of microbiota in the stomach, cecum and colon of pigs, and in the rumen of cows.  Imbalances in the gut bacteria were observed, along with elevated levels of harmful bacteria and deficiencies in copper and the amino acids tryptophan, tyrosine, and methionine.

A 2018 study published in Proceedings of the National Academy of Sciences showed that glyphosate affected honeybee and bumblebee gut microbial communities, and could be a factor in making bees more susceptible to environmental stressors and pathogens.

Glyphosate has been shown to be potent in its ability to degrade the tight junctions in the gut membrane wall.  Tight junctions serve as a firewall, regulating the absorption of water and micronutrients, and protecting the immune system from exposure to toxins that may be in the gut.

The environmental effects of GMO soy
University of Virginia economist Federico Ciliberto recently conducted a study into the environmental impact of GMO crops, in which data was collected from more than 10,000 US soybean and corn farmers operating between 1998 and 2011. The most shocking finding was the increase in glyphosate-resistant weeds, which meant farmers were having to spread more and more herbicides on their fields. Also noted in the study: “[T]he adoption of genetically modified soybeans correlated with a negative impact on the environment as increased herbicide use also increased contamination of local ecosystems.”

Still, 1.35 million metric tons of glyphosate were used in 2017.

Presently there are 38 countries that ban the cultivation of GMO crops, including Austria, Denmark, Ecuador, France, Germany, Italy, Kenya, Netherlands, Northern Ireland, Scotland, Wales, Norway, Peru, Poland, Switzerland, Saudi Arabia, Ukraine, and Venezuela.  These countries don’t allow GMO crops to be grown within their borders, but do allow importation from elsewhere.  Russia, meanwhile, has banned the cultivation and importation of GMO seeds and foods, including meat and dairy that have been fed GMO feed.

Destruction of rainforest and savanna
Since 1970, Brazil has destroyed 270,000 square miles of the Amazon Jungle, with the two largest contributors to deforestation being cattle and soy farming. Beyond the jungle, Brazil’s largest savanna land, the Cerrado, has now lost 40,541 square miles to soy production. The Cerrado is a vital storehouse for carbon dioxide. Ane Alencar, science director for the Amazon Environmental Research Institute says, “What many don’t see is the connection between the soybean-fed meat on their plates and the steady decline of one of the world’s great carbon sinks, a bulwark against global warming.”

Destroying the diversity of the rainforests and savannas also extinguishes entire plant and animal species, contaminates water, and fuels soil erosion.

There is growing evidence that glyphosate affects soil and rhizosphere microbial communities, decreases root colonization by beneficial mycorrhizae fungi, and has severe, fatal effects on earthworms.

One nation under soy
Soy in commercial complete horse feeds needs serious consideration. Even for horses that seem to tolerate soy well, there are the glyphosate and GMO concerns. With farmers being encouraged to use glyphosate as a desiccant for hay, our horses are now being exposed continuously to Roundup, and yet no feed company or hay dealer is testing for herbicide residue.

I work with a lot of clients whose horses have low-grade GI symptoms: watery manure, runny manure, gas. What’s amazing is that a combination of soy-free diet and a good probiotic can turn these horses around, when even antibiotic therapy won’t completely fix the problem.

A few further observations:

  • Horse attitudes can improve when the animal is taken off soy.
  • Overweight horses lose some of the inflammation when soy is out of their diet.
  • Mares have less severe PMS symptoms when no longer on soy.


We can no longer ignore the environmental consequences of Big Ag. Even for our horses with soy tolerance and glyphosate tolerance, the effect of monoculture farming and the increase in herbicide use is affecting our soils and our pollinators. The destruction of rain forest and savanna has real consequences. Climate change is here, no matter what the politicians say.

Soy ingredients in horse feeds are inexpensive and plentiful. Their use is defended by feed companies who talk about the protein, fiber, and fat content, but frankly, I think it’s best to feed organic alfalfa pellets with camelina oil or hemp seed oil. BioStar does not use soy products in any of our formulas. Let’s save the soy for miso and soy sauce.


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