Horses that have poor hoof growth, poor coat quality, or loss of muscle mass might be affected by a protein deficiency in their diet. Low milk production in lactating mares and flagging stamina might also be signs of deficiency.
This could be due to insufficient total protein in the diet or because the body does not have enough of certain essential amino acids to synthesize proteins.
Lysine is considered the first rate limiting amino acid in the horse’s diet. This means that protein synthesis in your horse’s body is typically limited to the rate at which this nutrient is available.
if you suspect a protein deficiency or amino acid imbalance, consider supplementing the diet with L-lysine to improve the body’s protein synthesis capacity.
Methionine and threonine are often considered the second and third limiting amino acids for horses. Supplementing with these three amino acids together can correct most amino acid deficiencies in equine diets and optimize protein synthesis in the body.
According to the NRC (2007) , the minimum amount of lysine that horses need is 18 grams per day for a 500 kg horse at maintenance. However, optimal levels intake are estimated at 27 grams per day for a 500 kg horse.
Exercising horses require more of this amino acid. Depending on how much exercise your horse gets, the requirements range from 2 to 8 grams of additional lysine per day (29 to 35 grams) for light to heavy exercise.
In general, the lysine requirement is calculated as 4.3% of the dietary crude protein requirement for your horse. At different life stages, the protein and lysine requirements of your horse change.
For weanlings (4-10 months of age), the lysine requirement is 29 grams per day for a 170 kg weanling. This increases to 48 to 50 grams per day for yearlings (11-17 months of age).
ROLES OF LYSINE IN THE BODY
Lysine enhances calcium absorption from the gut in all mammals and minimizes calcium excretion by the kidney. This makes calcium more available to form healthy bones and support normal muscle and nerve function. 
Lysine is also essential for the formation of collagen – a key structural protein in skin and bones. Supplementing this amino acid might be particularly beneficial in growing or aging horses to support healthy tissues, especially healthy bones.
In mammals, carnitine is synthesized from lysine. Carnitine is a vitamin-like nutrient that is important for the first steps of beta-oxidation – the process by which energy is made from fat.
Exercising horses could benefit from lysine supplementation to help them get energy efficiently from the fat in their body. This could support athletic performance.
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.
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