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==1. What is Taurine?==

==What is Taurine?==

Taurine (2-aminoethanesulfonic acid) is a '''naturally occurring sulphonic acid produced in the liver''' as an end product of [[Methionine and Cysteine - Nutrition|cysteine]] metabolism. Taurine is not incorporated into proteins but found free in animal tissues; the highest concentrations are found in brain, heart, and skeletal muscle. Although commonly referred to as an amino acid it lacks a carboxyl group and is not classified as a true amino acid. '''Dogs can synthesise taurine from dietary precursors''' and are typically able produce amounts sufficient to meet daily needs. '''Cats are unable to produce adequate amounts of taurine to meet requirements and pre-formed taurine is required in the diet.'''  

Taurine (2-aminoethanesulfonic acid) is a '''naturally occurring sulphonic acid produced in the liver''' as an end product of [[Methionine and Cysteine - Nutrition|cysteine]] metabolism. Taurine is not incorporated into proteins but found free in animal tissues; the highest concentrations are found in brain, heart, and skeletal muscle. Although commonly referred to as an amino acid it lacks a carboxyl group and is not classified as a true amino acid. '''Dogs can synthesise taurine from dietary precursors''' and are typically able produce amounts sufficient to meet daily needs. '''Cats are unable to produce adequate amounts of taurine to meet requirements and pre-formed taurine is required in the diet.'''  

==2. Why is it Important?==

==Why is it Important?==

The importance of taurine is related to its roles in many different organ systems, especially brain and heart. Deficiency results in serious and sometimes irreversible conditions. Therefore it is important to have an understanding of how animals may develop deficiencies and be aware of strategies to avoid or treat deficiencies.  

The importance of taurine is related to its roles in many different organ systems, especially brain and heart. Deficiency results in serious and sometimes irreversible conditions. Therefore it is important to have an understanding of how animals may develop deficiencies and be aware of strategies to avoid or treat deficiencies.  

==3. Roles in the Body==

==Roles in the Body==

'''Taurine is used in the conjugation of bile acids into bile salts in both dogs and cats'''. Cats only use taurine to form bile salts while dogs are able to conjugation bile acids to either taurine or glycine depending on availability of either amino acid<ref>Rabin J, et al. Dietary influences on bile acid conjugation in the cat. J Nutr 1976;106:1241-1246.</ref><ref>Wildgrube HJ, et al. Naturally occurring conjugated bile acids, measured by high-performance liquid chromatography, in human, dog, and rabbit bile. J Chrom. 1986;353:207-13.</ref>. Cats are unable to switch conjugation to glycine like dogs and other species and have an obligate loss of taurine in faeces. Bile salts are deconjugated in the intestinal lumen by bacteria and the deconjugated bile acids return to the liver via enterohepatic circulation. Taurine is then either absorbed by enterocytes, excreted in faeces, or further utilized by intestinal bacteria.  

'''Taurine is used in the conjugation of bile acids into bile salts in both dogs and cats'''. Cats only use taurine to form bile salts while dogs are able to conjugation bile acids to either taurine or glycine depending on availability of either amino acid<ref>Rabin J, et al. Dietary influences on bile acid conjugation in the cat. J Nutr 1976;106:1241-1246.</ref><ref>Wildgrube HJ, et al. Naturally occurring conjugated bile acids, measured by high-performance liquid chromatography, in human, dog, and rabbit bile. J Chrom. 1986;353:207-13.</ref>. Cats are unable to switch conjugation to glycine like dogs and other species and have an obligate loss of taurine in faeces. Bile salts are deconjugated in the intestinal lumen by bacteria and the deconjugated bile acids return to the liver via enterohepatic circulation. Taurine is then either absorbed by enterocytes, excreted in faeces, or further utilized by intestinal bacteria.  

Taurine also plays a role in normal retinal and myocardial function, osmoregulation, platelet aggregation, modulation of calcium flux within cells, reproduction, and immune response. There are three established clinical syndromes related to taurine deficiency: feline central retinal degeneration (FCRD), dilated cardiomyopathy (DCM), and reproductive failure.  

Taurine also plays a role in normal retinal and myocardial function, osmoregulation, platelet aggregation, modulation of calcium flux within cells, reproduction, and immune response. There are three established clinical syndromes related to taurine deficiency: feline central retinal degeneration (FCRD), dilated cardiomyopathy (DCM), and reproductive failure.  

==4. Consequences of Taurine Deficiency==

==Consequences of Taurine Deficiency==

===Dog:===  

===Dog:===  

Taurine-deficient DCM has been reported in dogs<ref name="Fascetti">Fascetti AJ, et al. Taurine deficiency in dogs with dilated cardiomyopathy: 12 cases (1997-2001). JAVMA 2003;223:1137-1141.</ref><ref name="Belanger">Belanger MC, et al. Taurine-deficient dilated cardiomyopathy in a family of golden retrievers. JAAHA 2005;41:284-91.</ref><ref name="Kittleson">Kittleson MD, et al. Results of the multicenter spaniel trial (MUST): taurine- and carnitine-responsive dilated cardiomyopathy in American cocker spaniels with decreased plasma taurine concentration. JVIM 1997;11:204-211.</ref><ref name="Backus">Backus RC, et al. Low Plasma Taurine Concentration in Newfoundland Dogs is Associated with Low Plasma Methionine and Cyst(e)ine Concentrations and Low Taurine Synthesis. J Nutr 2006;136:2525-2533.</ref>. This can occur despite being fed commercial diets labelled as complete and balanced when the diet provides inadequate supply of sulphur amino acids without additional taurine supplementation; contains poorly digestibly proteins<ref name="Torres">Torres CL, et al. Taurine status in normal dogs fed a commercial diet associated with taurine deficiency and dilated cardiomyopathy. JAPAN(Berl) 2003;87:359-72.</ref>; contains a higher fibre content that promotes a high faecal losses of bile salts<ref>Delaney SJ, et al. Plasma and whole blood taurine in normal dogs of varying size fed commercially prepared food. JAPAN(Berl) 2003 Jun;87(5-6):236-44.</ref>; or is fed to a large breed dog with a low capacity for synthesis of taurine<ref name="Backus"/><ref>Ko KS, et al. Differences in taurine synthesis rate among dogs relate to differences in their maintenance energy requirement J Nutr 2007;137:1171–1175.</ref>. Regardless of cause, taurine supplementation in these dogs appears to reverse some of the changes in cardiac function<ref name="Fascetti"/><ref name="Belanger"/><ref name="Kittleson"/>. Taurine supplementation is recommended for all dogs presenting with DCM until taurine deficiency has been ruled out.  

Taurine-deficient DCM has been reported in dogs<ref name="Fascetti">Fascetti AJ, et al. Taurine deficiency in dogs with dilated cardiomyopathy: 12 cases (1997-2001). JAVMA 2003;223:1137-1141.</ref><ref name="Belanger">Belanger MC, et al. Taurine-deficient dilated cardiomyopathy in a family of golden retrievers. JAAHA 2005;41:284-91.</ref><ref name="Kittleson">Kittleson MD, et al. Results of the multicenter spaniel trial (MUST): taurine- and carnitine-responsive dilated cardiomyopathy in American cocker spaniels with decreased plasma taurine concentration. JVIM 1997;11:204-211.</ref><ref name="Backus">Backus RC, et al. Low Plasma Taurine Concentration in Newfoundland Dogs is Associated with Low Plasma Methionine and Cyst(e)ine Concentrations and Low Taurine Synthesis. J Nutr 2006;136:2525-2533.</ref>. This can occur despite being fed commercial diets labelled as complete and balanced when the diet provides inadequate supply of sulphur amino acids without additional taurine supplementation; contains poorly digestibly proteins<ref name="Torres">Torres CL, et al. Taurine status in normal dogs fed a commercial diet associated with taurine deficiency and dilated cardiomyopathy. JAPAN(Berl) 2003;87:359-72.</ref>; contains a higher fibre content that promotes a high faecal losses of bile salts<ref>Delaney SJ, et al. Plasma and whole blood taurine in normal dogs of varying size fed commercially prepared food. JAPAN(Berl) 2003 Jun;87(5-6):236-44.</ref>; or is fed to a large breed dog with a low capacity for synthesis of taurine<ref name="Backus"/><ref>Ko KS, et al. Differences in taurine synthesis rate among dogs relate to differences in their maintenance energy requirement J Nutr 2007;137:1171–1175.</ref>. Regardless of cause, taurine supplementation in these dogs appears to reverse some of the changes in cardiac function<ref name="Fascetti"/><ref name="Belanger"/><ref name="Kittleson"/>. Taurine supplementation is recommended for all dogs presenting with DCM until taurine deficiency has been ruled out.  

#'''Deafness''': Taurine deficiency has been associated with delayed auditory brainstem- evoked response maturation in cats resulting in hearing loss<ref>Vallecalle-Sandoval MH, et al. Comparison of the developmental changes of the brainstem auditory evoked response (BAER) in taurine-supplemented and taurine-deficient kittens. Int J Dev Neurosci 1991;9(6):571-9.</ref>.

#'''Deafness''': Taurine deficiency has been associated with delayed auditory brainstem- evoked response maturation in cats resulting in hearing loss<ref>Vallecalle-Sandoval MH, et al. Comparison of the developmental changes of the brainstem auditory evoked response (BAER) in taurine-supplemented and taurine-deficient kittens. Int J Dev Neurosci 1991;9(6):571-9.</ref>.

==5. Toxicity==

==Toxicity==

There are no known reports of toxicity either acute or chronic related to feeding high doses of taurine. Given the body’s ability to excrete excess taurine in faeces and degradation by intestinal microbes, toxicity risk is low.  

There are no known reports of toxicity either acute or chronic related to feeding high doses of taurine. Given the body’s ability to excrete excess taurine in faeces and degradation by intestinal microbes, toxicity risk is low.  

==7. Dietary Sources==

==Dietary Sources==

Taurine is found in animal proteins, with highest concentrations in skeletal and heart muscle, though concentrations will vary by species<ref name="Spitze">Spitze AR, et al. Taurine concentrations in animal feed ingredients; cooking influences taurine content. JAPAN(Berl) 2003 Aug;87(7-8):251-62.</ref>. Taurine is also lower in dairy and egg proteins and it limited to absent in plant proteins. Vegetarian andvegan diets will cause taurine deficiency in cats if not supplemented adequately; vegetarian and vegan diets for dogs often contain inadequate sulphur amino acid precursors and are at a high risk for causing taurine deficiency in dogs. Synthetic forms of taurine are available for vegetarian and vegan diets. Diets severely restricted in protein may provide insufficient quantities of amino acids to support adequate taurine production in dogs<ref>Sanderson SL, et al. Effects of dietary fat and L-carnitine on plasma and whole blood taurine concentrations and cardiac function in healthy dogs fed protein-restricted diets. AJVR 2001;62:1616-1623.</ref>.

Taurine is found in animal proteins, with highest concentrations in skeletal and heart muscle, though concentrations will vary by species<ref name="Spitze">Spitze AR, et al. Taurine concentrations in animal feed ingredients; cooking influences taurine content. JAPAN(Berl) 2003 Aug;87(7-8):251-62.</ref>. Taurine is also lower in dairy and egg proteins and it limited to absent in plant proteins. Vegetarian andvegan diets will cause taurine deficiency in cats if not supplemented adequately; vegetarian and vegan diets for dogs often contain inadequate sulphur amino acid precursors and are at a high risk for causing taurine deficiency in dogs. Synthetic forms of taurine are available for vegetarian and vegan diets. Diets severely restricted in protein may provide insufficient quantities of amino acids to support adequate taurine production in dogs<ref>Sanderson SL, et al. Effects of dietary fat and L-carnitine on plasma and whole blood taurine concentrations and cardiac function in healthy dogs fed protein-restricted diets. AJVR 2001;62:1616-1623.</ref>.

Processing and cooking of foods will also influence taurine content and animal requirements. Wet food diets promote higher intestinal bacterial population and will increase loss of taurine in cats<ref>Anantharaman-Barr G, et al. Fecal bile acid excretion and taurine status in cats fed canned and dry diets. J Nutr 1994;124:2546S-2551S.</ref><ref>Kim SW, et al. Dietary antibiotics decrease taurine loss in cats fed a canned heat-processed diet. J Nutr 1996;126:509-515.</ref>; boiling increases meat taurine loss compared to roasting or baking<ref name="Spitze"/>, and dietary fibre content will influence rate of taurine loss<ref name="Torres"/><ref>Stratton-Phelps M, et al. Dietary rice bran decreases plasma and whole-blood taurine in cats. J Nutr 2002;132:1745S-1747S. </ref>. Vegetarian diets are deficient in taurine, in addition to other key nutrients for cats, and should not be fed without proper supplementation.

Processing and cooking of foods will also influence taurine content and animal requirements. Wet food diets promote higher intestinal bacterial population and will increase loss of taurine in cats<ref>Anantharaman-Barr G, et al. Fecal bile acid excretion and taurine status in cats fed canned and dry diets. J Nutr 1994;124:2546S-2551S.</ref><ref>Kim SW, et al. Dietary antibiotics decrease taurine loss in cats fed a canned heat-processed diet. J Nutr 1996;126:509-515.</ref>; boiling increases meat taurine loss compared to roasting or baking<ref name="Spitze"/>, and dietary fibre content will influence rate of taurine loss<ref name="Torres"/><ref>Stratton-Phelps M, et al. Dietary rice bran decreases plasma and whole-blood taurine in cats. J Nutr 2002;132:1745S-1747S. </ref>. Vegetarian diets are deficient in taurine, in addition to other key nutrients for cats, and should not be fed without proper supplementation.

==8. Diagnosing Taurine Deficiency==

==Diagnosing Taurine Deficiency==

Diagnosis of taurine deficiency is based on compatible clinical signs and demonstration of low fasting plasma and low whole blood taurine concentration. Deficient or inadequate sulphur amino acid content in the diet may also help establish a diagnosis although difficult to analyse. Fasting plasma concentration reflects the labile pool of taurine and is prone to processing errors. A better indicator of taurine status is provided by assaying whole blood taurine content as this is believed to reflect tissue levels. Normal plasma taurine concentration in cats range from 50-250 nmol/mL and 60-145 nmol/ml in dogs. Results < 40 nmol/mL is highly suggestive of a deficiency in cats and dogs. Whole blood taurine concentrations are normally > 300 nmol/mL in cats and > 200 nmol/mL in dogs and values < 160 nmol/mL are considered to reflect a deficient state although many clinical cases have < 50 nmol/ml.

Diagnosis of taurine deficiency is based on compatible clinical signs and demonstration of low fasting plasma and low whole blood taurine concentration. Deficient or inadequate sulphur amino acid content in the diet may also help establish a diagnosis although difficult to analyse. Fasting plasma concentration reflects the labile pool of taurine and is prone to processing errors. A better indicator of taurine status is provided by assaying whole blood taurine content as this is believed to reflect tissue levels. Normal plasma taurine concentration in cats range from 50-250 nmol/mL and 60-145 nmol/ml in dogs. Results < 40 nmol/mL is highly suggestive of a deficiency in cats and dogs. Whole blood taurine concentrations are normally > 300 nmol/mL in cats and > 200 nmol/mL in dogs and values < 160 nmol/mL are considered to reflect a deficient state although many clinical cases have < 50 nmol/ml.