Lysine - Nutrition

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What is Lysine?

Lysine is an essential amino acid for dogs and cats. Lysine is classified as a ketogenic amino acid and contains a long, positively charged side chain. Dietary lysine is absorbed by a dibasic amino acid transporter in the small intestine (particularly the jejunum) and plasma lysine is actively reabsorbed in the proximal tubule of the kidney.

Why is it Important?

Lysine and lysine-containing compounds, such as hydroxylysine found in collagen; play an important role in the secondary structure of proteins; the positively charged side chain is used for binding to other molecules, such as DNA during replication; and lysine acetylation also plays a role in regulating cellular metabolism[1][2]. Inherited defects in the transporter for dibasic amino acids can result in poor absorption of lysine (as well as the other dibasic amino acids cystine, ornithine, and arginine) from the intestinal mucosa and poor reabsorption of plasma lysine in the renal tubule[3].

Roles in the Body

Lysine plays a key role in determining the secondary structure of proteins. It is a precursor of hydroxylysine, a key component of collagen, and of carnitine, which plays an important role in energy metabolism by transporting fatty acids into the mitochondria. Lysine can be de-aminated by intestinal bacterial to form the foul-smelling compound cadaverine[1].


Lysine antagonises arginine induced promotion of herpes virus in vitro[4], and oral supplementation (400 mg PO q 24h to 500 mg PO q 12h) has been shown to decrease both viral shedding and severity of conjunctivitis in herpes virus-infected cats[5][6]. However other studies[7][8] have not shown an effect of lysine supplementation on non-ophthalmological herpes virus, Chlamydophila, or calicivirus shedding or on the severity of upper respiratory infection signs.

Consequences of Lysine Deficiency


Short-term feeding of a lysine deficient diet resulted in depressed food intake and weight loss in growing puppies[9]. Effects of longer term dietary lysine deficiency have not been reported in dogs.


Short-term feeding (10d) of a lysine-deficient diet caused weight loss in growing kittens[10]. Effects of longer term lysine deficiency have not been reported in cats.


Lysine (either dietary or as a single amino acid supplement) can antagonize arginine absorption and excess lysine intake can cause clinical findings consistent with arginine deficiency in puppies (e.g. vomiting, lethargy, weight loss and urinary orotic acid excretions)[11]. This effect has not been demonstrated in kittens fed up to 8 times the daily lysine requirement[12].

Dietary Sources

Sufficient levels of lysine are found in animal and plant protein sources, such as muscle meat, eggs, dairy protein (e.g. casein), cereal grains, and pulses (i.e. legumes). Cereal grains contain lower levels of lysine and this is often the first limiting amino acid in dogs and cats fed cereal grain-based diets. Lysine also readily forms Maillard reaction products with glucose during heat processing[13], which can limit dietary lysine absorption.

Diagnosing Lysine Deficiency

Diagnosis of lysine deficiency is based on fasted plasma amino acids.


  1. 1.0 1.1 National Research Council (NRC). Protein and Amino Acids. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p. 125-126.
  2. Zhao S, et al. Regulation of cellular metabolism by lysine acetylation. Science 2010;327:1000-1004.
  3. Hoppe A, et al. Urinary excretion of amino acids in normal and cystinuric dogs. Br Vet J 1993;149:253-68.
  4. Maggs DJ, et al. Effects of L-lysine and L-arginine on in vitro replication of feline herpesvirus type-1. AJVR 2000;61:1474-1478.
  5. Maggs DJ, et al. Efficacy of oral supplementation with L-lysine in cats latently infected with feline herpesvirus. AJVR 2003;64:37-42.
  6. Stiles J, et al. Effect of oral administration of L-lysine on conjunctivitis caused by feline herpesvirus in cats. AJVR 2002;63:99-103.
  7. Maggs DJ, et al. Effects of dietary lysine supplementation in cats with enzootic upper respiratory disease. J Fel Med Surg 2007;9:97-108.
  8. Drazenovich T, et al. Effects of dietary lysine supplementation on upper respiratory and ocular disease and detection of infectious organisms in cats within an animal shelter. AJVR 200;70:1391-400.
  9. Milner JA. Assessment of indispensable and dispensable amino acids for the immature dog. J Nutr 1979;109:1161-1167.
  10. Rogers QR and Morris JG. Essentiality of amino acids for the growing kitten. J Nutr 1979;109:718-723.
  11. Czarnecki GL, et al. Antagonism of arginine by excess dietary lysine in growing dogs. J Nutr 1985;1115:743-752.
  12. Taylor TP, et al. Optimizing the pattern of essential amino acids as the sole source of dietary nitrogen supports near maximal growth in kittens. J Nutr 1996;126:2243-2252.
  13. van Rooijen C, et al. The Maillard reaction and pet food processing: effects on nutritive value and pet health. Nutr Res Rev 2013;26:130-148.

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