Soy Safety: Depends on the Source, Nutritionists Say

Horses have varying protein requirements, depending on stage of life or performance level. Protein, the essential building block for new cellular growth, provides the amino acids necessary for maintaining all normal body functions in a horse, from synthesis and release of hormones to formation and repair of muscle and other soft tissues. Soy has long been considered a reliable source of protein for horses. But is it really safe?

There are some inherent problems with feeding soybean protein, according to Jack Grogan, CN, vice president of research and development at Uckele Health & Nutrition in Blissfield, Mich. "Soy protein by itself can directly interfere with hormonal balance and be pro-inflammatory, increasing the metabolic stress load and affecting immune function," he said. "We feel feed enhancers that use soy protein are not in the horse's best interest."

However, Amy M. Gill, PhD, an equine nutritionist from Lexington, Ky., has a different perspective.

"Horses need vegetarian sources of protein to supply amino acids. As far as we know, soy protein provides the closest match to equine amino acid requirements," said Gill. "Many of the human soy-related problems reported in the news are coming from women who overconsume soy protein, affecting their reproductive hormones, or from people who are truly allergic to soy products."

Gill continued, "Because horses are strict herbivores, they can have completely different metabolic responses to digesting individual ingredients than omnivorous humans do, so the effect of these ingredients could be different. No data currently exists, that I'm aware of, that shows soy protein has a negative effect on horses when it's fed in reasonable amounts, such as those included in nutritionally balanced horse feeds."

But Grogan also cautions owners not to throw the soy baby out with the bathwater. "While soy protein can have negative health consequences, cold-pressed, unrefined soybean oil has beneficial antioxidant effects, including stabilizing blood sugar and improving metabolic balance. We recommend soy oil as a positive addition to a well-rounded feeding program," he said.

What's the best nutritional advice? Whether you choose to use soy products or not, Gill advises working with a reputable company or manufacturer. "Use a pre-formulated, balanced feed suited for the physiologic needs of your horse," she said. "Provide adequate forage and fresh water. And, be sure you're following the manufacturer's recommendations for feeding."

If your horse exhibits physiological or behavioral changes and you suspect a dietary cause, Gill recommends testing before leaping to any conclusions. "Anytime there is a significant and/or dramatic change in a horse, always consult with your veterinarian," she advised. "At a minimum, run blood tests, including a complete blood count (CBC) and chemistry panel, to eliminate any pathologies."

About the Author

Lisa Kemp

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