E: 92 Soy as a Feed Ingredient and Protein Info You Need to Hear
Fri Feb 06 2026
Send Audrey a Text to get your question answered on the show
Recently there was some push back around soy as an ingredient and more over as an amino acid requirement in feed and or ration balancers. The good ol “show me the scientific evidence” came right out. So lets talk about soy as an ingredient and why it matters even for horses that don’t have a direct sensitivity or allergy for soy. Today we will talk through a few different aspects including soys anti-nutrient properties, glyphosate issues, and the all important “what about amino acids then?”
Sources
Lysine as the first limiting amino acid in horses
National Research Council (NRC). (2007).
Nutrient Requirements of Horses (6th rev. ed.).
Washington, DC: National Academies Press.
Establishes lysine as the first limiting amino acid in typical equine diets and emphasizes amino acid balance over crude protein.
Lysine, threonine, and methionine requirements and ratios
Mansilla, W. D., et al. (2020).
Amino acid requirements in horses: Current knowledge and future perspectives.
Animals, 10(4), 682.
https://doi.org/10.3390/ani10040682
Reviews essential amino acid requirements in horses; discusses lysine as first limiting, with threonine and methionine following depending on diet.
Threonine as a secondary limiting amino acid
Harris, P. A., & Pagan, J. D. (1999).
Protein and amino acid nutrition in the performance horse.
Proceedings of the Equine Nutrition Conference, Kentucky Equine Research.Discusses lysine as first limiting and identifies threonine as potentially limiting when lysine is corrected.
Functional importance of lysine and threonine (equine studies)
Zhang, L., et al. (2023).
Effects of lysine and threonine supplementation on milk yield, amino acid metabolism, and fecal microbiota of lactating mares.
Journal of Animal Science and Biotechnology, 14, 84.
https://doi.org/10.1186/s40104-023-00884-5
Demonstrates physiological and metabolic effects of lysine and threonine supplementation in horses.
Balanced amino acid profiles vs crude protein
Graham-Thiers, P. M., & Kronfeld, D. S. (2005).
Amino acid supplementation improves muscle mass in exercising horses fed diets adequate in crude protein.
Journal of Nutrition, 135(9), 2144–2148.
https://doi.org/10.1093/jn/135.9.2144
Shows that horses fed “adequate” crude protein still benefit from targeted amino acid supplementation.
Ideal protein concept (amino acid balance over quantity)
Wu, G. (2014).
Dietary requirements of synthesizable amino acids by animals: A paradigm shift in protein nutrition.
Journal of Animal Science and Biotechnology, 5, 34.
https://doi.org/10.1186/2049-1891-5-34
Introduces and supports the concept that amino acid balance determines protein utilization more than total protein intake.
Why crude protein is a poor metric
Crude protein vs usable protein
Millward, D. J., et al. (2008).
Protein quality a
Find all the Resource Listed Here: linktr.ee/equineenergymed
Audrey is not an MD or DVM and has never implied or claimed to be either. Audrey holds a Doctoral Degree of Traditional Naturopathy and a Masters Degree in Science. She created an evidenced-based anti-inflammatory nutrition program for equine and has successfully helped over 10k horses. This information is not meant to diagnose, prescribe for, treat, or cure, and is not a replacement for your veterinarian. These are my personal interpretations based on my education, skill and clinical experience.
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Send Audrey a Text to get your question answered on the show Recently there was some push back around soy as an ingredient and more over as an amino acid requirement in feed and or ration balancers. The good ol “show me the scientific evidence” came right out. So lets talk about soy as an ingredient and why it matters even for horses that don’t have a direct sensitivity or allergy for soy. Today we will talk through a few different aspects including soys anti-nutrient properties, glyphosate issues, and the all important “what about amino acids then?” Sources Lysine as the first limiting amino acid in horses National Research Council (NRC). (2007). Nutrient Requirements of Horses (6th rev. ed.). Washington, DC: National Academies Press. Establishes lysine as the first limiting amino acid in typical equine diets and emphasizes amino acid balance over crude protein. Lysine, threonine, and methionine requirements and ratios Mansilla, W. D., et al. (2020). Amino acid requirements in horses: Current knowledge and future perspectives. Animals, 10(4), 682. https://doi.org/10.3390/ani10040682 Reviews essential amino acid requirements in horses; discusses lysine as first limiting, with threonine and methionine following depending on diet. Threonine as a secondary limiting amino acid Harris, P. A., & Pagan, J. D. (1999). Protein and amino acid nutrition in the performance horse. Proceedings of the Equine Nutrition Conference, Kentucky Equine Research.Discusses lysine as first limiting and identifies threonine as potentially limiting when lysine is corrected. Functional importance of lysine and threonine (equine studies) Zhang, L., et al. (2023). Effects of lysine and threonine supplementation on milk yield, amino acid metabolism, and fecal microbiota of lactating mares. Journal of Animal Science and Biotechnology, 14, 84. https://doi.org/10.1186/s40104-023-00884-5 Demonstrates physiological and metabolic effects of lysine and threonine supplementation in horses. Balanced amino acid profiles vs crude protein Graham-Thiers, P. M., & Kronfeld, D. S. (2005). Amino acid supplementation improves muscle mass in exercising horses fed diets adequate in crude protein. Journal of Nutrition, 135(9), 2144–2148. https://doi.org/10.1093/jn/135.9.2144 Shows that horses fed “adequate” crude protein still benefit from targeted amino acid supplementation. Ideal protein concept (amino acid balance over quantity) Wu, G. (2014). Dietary requirements of synthesizable amino acids by animals: A paradigm shift in protein nutrition. Journal of Animal Science and Biotechnology, 5, 34. https://doi.org/10.1186/2049-1891-5-34 Introduces and supports the concept that amino acid balance determines protein utilization more than total protein intake. Why crude protein is a poor metric Crude protein vs usable protein Millward, D. J., et al. (2008). Protein quality a Find all the Resource Listed Here: linktr.ee/equineenergymed Audrey is not an MD or DVM and has never implied or claimed to be either. Audrey holds a Doctoral Degree of Traditional Naturopathy and a Masters Degree in Science. She created an evidenced-based anti-inflammatory nutrition program for equine and has successfully helped over 10k horses. This information is not meant to diagnose, prescribe for, treat, or cure, and is not a replacement for your veterinarian. These are my personal interpretations based on my education, skill and clinical experience.