Mad Barn’s bulk L-threonine powder is a 99% pure crystalline form of the essential amino acid threonine. As a nutritional supplement, it is commonly used in horses to support optimal gut health and nutrient absorption.
Threonine is a building block of protein and one of the main limiting amino acids in horse diets, along with methionine and lysine. If your horse does not get enough of the rate limiting amino acids in their diet, it can impair protein synthesis and result in immune dysfunction, problems with growth and poor performance.
Providing adequate levels of threonine can support optimal rates of protein synthesis in all cells of the body. This helps ensure that tissues have the structural proteins, enzymes, and immune components that they need for optimal function.
According to the NRC (2007), threonine requirements for horses can be estimated as 62% of lysine requirement. Threonine should account for 2.7% of dietary crude protein intake. A 500 kg horse at maintenance requires 17 grams per day of threonine for optimal protein synthesis. 
The requirement for exercising horses is estimated at 1.2 to 4.7 grams of additional threonine (19 to 22 grams total) depending on the intensity of exercise. This will help exercising horses meet the demand for protein synthesis during exercise recovery.
Young, growing animals will also have a higher demand for amino acids. For weanlings (4-10 months of age), the threonine requirement is estimated at 18 g per day for a 170 kg weanling. This increases to 29 g per day for yearlings (11-17 months of age).
Amino acids are the building blocks for protein in the body. Optimal protein synthesis can only occur when all essential amino acids are sufficiently available.
In horses, lysine is the first limiting amino acid meaning it is most likely to be low in the diet and protein synthesis rates will not be optimal until there is enough lysine available. Methionine and threonine are often considered the second or third limiting amino acids for horses.
Horses that have poor hoof growth, poor coat quality, or loss of muscle mass might have a protein deficiency in their diet. Low milk production in lactating mares and poor stamina are additional signs of deficiency.
Ensuring that your horse receives adequate levels of lysine, methionine, and threonine in their diet could correct amino acid imbalances, supporting normal function of all tissues in the body.
Roles of Threonine in the Body
Threonine is important for supporting a healthy gut and digestive function. In other animals it has been shown that most dietary threonine (60-90%) is used by the tissues of the gut.
Threonine is crucial for the production of mucin proteins which form a protective barrier in the intestine to prevent microbes in the gut from damaging intestinal cells. When dietary threonine is low, it will be prioritized for mucin production, which prevents it from being used for muscle growth or protein synthesis in other tissues. 
Horses often face conditions that can impair gut function. For example, high-grain diets in performance horses can cause microbial imbalances that injure the intestinal lining and lead to ulcers.
Providing performance horses supplemental threonine might help them handle high-grain diets and improve nutrient absorption leading to improved overall health and stamina.
You should always consult a qualified nutritionist before altering your feed program. Submit your horse’s diet for analysis online and one of our equine nutritionists will be happy to provide a complementary review.