Taurine is one of eleven essential amino acids required by cats and its requirement has been known for over 20 years. While most mammals are able to manufacture taurine from other sulphur containing amino acids (cystine and methionine), the cat's ability to process taurine is very limited. Furthermore, because of a unique metabolic pathway in the cat's liver, much of the taurine absorbed from the cat's diet is excreted in the bile by the liver. For these reasons, cats require a constant dietary intake of taurine to maintain adequate tissue levels.

Taurine is found in relatively high concentrations in a variety of tissue, including muscle, retina and the central nervous system. It is necessary for the normal development of most tissues and is required for optimum reproductive performance. Low plasma taurine concentrations can be responsible for fetal abortion and resorption, low birth rates and unthrifty kittens. Additional clinical manifestations of taurine deficiency include Feline Central Retinal Degeneration (FCRD) which is a progressive degeneration of the photo-receptor cells of the retina causing blindness. FCRD blindness resulting from taurine deficiency is irreversible.

In 1987, a study at the University of California (Davis) led to the discovery that not only did taurine deficiency lead to a form of feline heart disease called dilated cardiomyopathy, but that a diet supplemented with taurine (500 mg/day) would reverse the disease process. The impact of taurine on cardiomyopathy in other species appears to be relatively limited or ineffective.

Most pet food manufacturers responded to these findings by increasing the levels of taurine in both canned and dry foods. Veterinary nutritional texts have recommended levels closer to 500 mg/kg of dry matter. However, even these levels may not be high enough for some cats and levels being recommended today are even higher. The Canadian Veterinary Medical Association (CVMA), through its Pet Food Certification Program, recommends levels of 1000 mg/kg of dry matter for dry foods and 2000 mg/kg of dry matter in its canned products.

Although the number of cases of dilated cardiomyopathy have dramatically decreased in recent years, it is still occasionally seen in cats that are eating mainly canine foods (which do not require fortification with taurine) or home-made diets that are cereal-based and not meat-based. Most home-made diets are imbalanced in other ways, as well.

A number of major issues remain unanswered and complicate the rationale behind dietary recommendations of appropriate levels. Why only some cats develop clinical disease manifestations in response to depleted taurine concentrations remains unanswered. It is known that fibre can bind taurine availability. As a result, cats on a high fibre diet as part of a weight control program, may require higher than expected dietary taurine levels. Investigations have also shown that the feed formulation, the manufacturing process, and hence the type of diet (canned vs dry) may well have an effect on the availability of taurine.

Without more insight into these areas, it is difficult to determine what dietary levels are appropriate. It is clear that further investigation is necessary to better understand the complexities of taurine metabolism, bioavailability and life-stage idiosyncrasies in the feline.