Genetics may determine the basic colour of the cat, but other factors can affect the intensity or variation of the colour. These factors can be environmentally determined, as in the area we are about to discuss. Some interesting results were found from experiments regarding feline dietary tyrosine nutritional requirements and the effect on black cat's coat colour. Diets deficient in tyrosine caused the colour of hair to change from black to a reddish brown in cats and was associated with a reduction in melanin in hair.
What is tyrosine?
Image i a walsh, Flickr
Tyrosine is an amino acid that the cat synthesises from phenylalanine (another amino acid). Basically, Tyrosine is needed to make melanin, which is the major pigment in cats skin and hair, it gives us the wonderful colours. If you can't make tyrosine because you are missing the right enzyme, you don't make as much melanin. In an albino, this enzyme cannot be produced, and as a result, melanin cannot be produced and you end up with the pale skin and hair of the albino. Over activity of the enzyme can produce the opposite effect, with large areas of highly pigmented skin/hair or it can be associated with the nasty tumours on the skin, known as melanomas.
Tyrosinase is the action of the enzyme tyrosine on melanin, which causes a complex series of biochemical changes. Tyrosinase is also thermally liable (temperature sensitive).
A quick side note: Cats of the Himalayan series (colour points, minks, sepias (semi-albinos)) have heat-sensitive tyrosinase. Normal tyrosinase converts the amino acid tyrosine into melanin (pigment). In Himalayan cats with this enzyme that denatures at normal body temperatures, the colour is formed only on the colder extremities of the body (legs, tail ears, face). This is why Siamese cats get darker in winter and paler in summer. If you put socks on your Siamese for several weeks, it would end up with white markings on its feet.
The full pigmentation allele for the cat is (C/-). The Burmese cat or sepia cat allele (cb/cb) has slightly thermo-liable tyrosinase, the mink cat or Tonkinese allele (cb/cs) has slightly more thermo-liable tyrosinase and the colour point or Siamese (cs/cs) has even more thermo-liable tyrosinase. Then there are the true albino cats, which are lacking in the enzyme. The blue eye white albino cat (ca/ca) and the pink or red eyed white Albino cat (c/c). All these alleles are found on the same locus and all interact with the enzyme tyrosine.
Lack of the enzyme tyrosine is also related to the grey hair both humans and cats get as we age.
The current recommended feline dietary concentration is 4.5 g tyrosine plus 12 g phenylalanine/kg amino acids for growing kittens to ensure maximum growth rates and nutritional balance in the kitten's diet. However, several experiments have shown that is not sufficient in retaining a black cat's coat colour.
Results from the studies with cats fed diets with the above aromatic amino acid quantities and lower show that these levels are not sufficient to maintain a black cat's, rich black coat. Levels greater than this are needed. Black cats on diets deficient in phenylalanine + tyrosine found that their lovely black coat colour changed to a reddish brown. This was caused by a reduction in the melanin (pigment) in the hair, a decreased total melanin concentrations of tyrosine in plasma. Reddish hair colour or rusting was induced in cats fed tyrosine-deficient diets for 6 months and in black kittens born to queens that were given tyrosine-deficient diets during their pregnancy.
The cat and kittens black hair colour was maintained and/or restored by diets containing a high concentration of tyrosine.
Cats fed diets with "..<16 g phenylalanine + tyrosine developed 'red hair.' We confirmed the anecdotal reports that the black hair of cats can change from black to reddish brown. An aromatic amino acid concentration > or =18 g/kg is recommended for the prevention of visually discernible red hair in black-coated cats. Dietary concentrations >18 g total aromatic amino acids/kg diet promote a greater ratio of PTCA:total melanin in hair. " (Anderson et al, July 2002). Basically, cats needed to ingest more than 18g per kg of phenylalanine + tyrosine to maintain or restore a black cat or kittens rich coat colour. Levels less than 16g resulted in reddish hair colour on the black cat.
Not mentioned in these studies is what happens when a cat ingested too much tyrosine, anecdotal evidence suggests that the cat’s coat will darken more than it should (e.g. a chocolate cat may become almost black). It is worth thinking about.
So, are we feeding enough Tyrosine in our cat’s diets and how much is too much?
Should I just give my cat tyrosine if its coat is turning reddish in colour?
Before you rush out and start adding things to your cat's diet, please check with your veterinarian first. There are many other factors that can influence a cat's colouring. You should never supplement your cat's diet without consultation with your veterinarian. Without going into too much detail on the complex relationship of the cat's organs, vitamins, amino acids, here are just a few (but there are many more) factors that could be affecting the melanin.
Copper Deficiency: One of the early signs of copper deficiency in cats is loss of hair colour, or achromotrichia, and a change in the texture of the hair. The reason for the colour change is an alteration to the metabolism of tyrosine. Copper helps tyrosine work as a pigment factor.
Zinc Excess: Basically too much zinc in the diet may cause a copper deficiency, which, in turn, can cause an iron deficiency. As a result of the copper deficiency, you end up with above.
Thyroid, Kidneys and Liver: Again without going into too much detail basically, these three organs can also effect coat colour and all interact with tyrosine. Tyrosine is metabolised in the liver and tyrosine is necessary for synthesising thyroxin, a hormone produced by the thyroid gland
Cats that should avoid tyrosine supplements
- Cats with liver damage
- Pregnant cats should not take any amino acids without first consulting with your veterinarian
- Cats with an overactive thyroid
- Cats with a malignant melanoma
- Cats being treated for any serious illness or on any medications
Please remember always consult with your veterinarian before giving your cat any supplements.
Tyrosine is found naturally in meat, dairy and eggs.
"Red hair in black cats is reversed by addition of tyrosine to the diet. "MorrisJG, Yu S, Rogers QR. Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA. Cats J Small Anim Pract 2001 Apr;42(4):176-80
"Effect of low levels of dietary tyrosine on the hair colour of cats." Yu S, Rogers QR, Morris JG. Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis 95616, USA. J Nutr 2002 Jul;132(7):2037-42 Cats require more dietary phenylalanine or tyrosine for melanin deposition in hair than for maximal growth.
"Ensory Neuropahty in Cats maintained on Phenyl-Alanine/Tyrosine Deficient Diets". P.J. Dickinson, P. Anderson, D.C. Williams, L.D. Tripp, G.D. Shelton, R.A. LeCouteur. School of Veterinary Medicine, University of California, Davis, CA, and University of California-San Diego (Shelton), La Jolla, CA.
Various microbiology texts.