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A new theory about x-colour

by Jette Eva Madsen, 26.03.2003.

A few days ago, Judith Zuurveld sent me a number of articles about pet nutrition. To my great surprise some of the articles showed photos of cats with a colour that look identical to the group of chocolate-x-colored cats.

The articles presented the effect of low levels of dietary tyrosine on the hair color of cats. The research has been triggered by the reports from owners of dogs and cats that the coat color of their pets changed from black to reddish brown when given certain commercial pet foods with low contents of tyrosine.

It has been obvious for a long time that there are different causes for the different coat colors of the cats belonging to the x-colored Forest Cats. Some cats have a color that resembles golden. Some look like they were cinnamon or fawn. Yet another group of cats has a color that could perhaps be caused by dilute modifier. The last group of cats looks like traditional chocolate cats, and I have seen specimens of these cats in Norway, Sweden and Finland.

This is the reason why we find the results discussed in the articles mentioned above as extremely important information for the discussion about the x-color of NFOs and more specifically the group of chocolate-colored NFOs.

The color of the cat

The color of the skin and hair of mammals is primarily determined by the type and amount of melanin present. The melanin we find in hair is composed of a mixture of two pigments. The eumelanin that give brown and black pigments and pheomelanin that give yellow to reddish-brown pigment. The precursor of both pigments is dopaquinone, which is derived from tyrosine and its precursor phenylalanine.

The impact of low levels of tyrosine and phenylalanine

Low levels of dietary tyrosine result in the hair of black cats changing to reddish-brown in color. Similar changes occur in the black hair of kittens during foetal development when queens are given a low tyrosine diet. If such a cat with reddish-brown hair is given adequate tyrosine the color of the hair will revert to black.

Dietary recommendations for tyrosine

The current dietary recommendations for tyrosine for cats seem to be too low for maximum eumelanin production. Thus, the Association of American Feed Control Officials 2000 has recommended 8,8 g/kg diet for phenylalanine plus tyrosine in cat food for both growing kittens and adult cats. These recommendations will support the growth of kittens, but do not support full hair melanin synthesis by cats.

Why are these findings important for Forest Cats?

We must conclude that there is a distinct possibility that the chocolate color of the NFOs is based on the lack of tyrosine or phenylalanine in the diet or based on the fact that some families of cats need unusually high concentrations of tyrosine and phenylalanine in order to develop proper black pigment. It would therefore be a good idea to carry out tests with diets with different concentrations of tyrosine and phenylalanine on the cats in question, namely the chocolate-colored NFOs.