That is a pretty controversial topic these days, both for human consumption and for your animals.
Add in how common genetically modifiied (GMO) soy has become, and it’s partner glyphosate, and you really stir the pot.
I personally do still use soy for my horses and goats.
Soy is an excellent source of the amino acid lysine. Lysine, threonine and arginine are the most important amino acids that build muscle. Dynamite HES has earned the knickname “topline in a bag” for a good reason. High fat moderate protein soybean is also a great diet option for horses that cannot handle grain. HES also helps build fat reserves. See this post for more on building fat reserves and muscle in goats. The basic chemistry applies to horses also.
Soy should be heated, to destroy trypsin inhibitors. Raw soy should never be fed to livestock. A trypsin inhibitor reduces the activity of trypsin. Trypsin is an enzyme that is necessary for protein digestion.
Isoflavones are another controversial soy ingredient. Isoflavones are phytoestrogens, or mimic estrogen hormones. Heat treating should reduce isoflavones. Additionally, there is some doubt that soybeans in moderate amount actually pose a risk. This was a well-balanced and well-researched article about human soy consumption. The basic biology principles apply across species though. http://veganskeptic.blogspot.com/2009/11/dangers-of-phytoestrogens.html
Finally, when in doubt, muscle test! Or dowse! Or use the reflex points! Your body, and your horse’s body, will tell you what is beneficial and what is harmful. No matter what the studies do or do not say, trust your testing results. If you don’t know how to test, check out my book The Energetic Goat and watch for a future blog post on testing.
What I have found for myself is that my goats and horses both muscle test well for Dynamite’s soy product HES. I test poorly for any soybean products including fermented products. Each body is different. I trust the test.
These statements have not been evaluated by the Food and Drug Administration or American Veterinary Medical Association, and are not intended to diagnose, treat, cure or prevent any disease. Always consult your veterinarian about any changes to your animal’s health program.