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Did you know that black cats can lose their colour and their fur (hair) can turn a reddish-brown if they don’t have enough meat in their diet?

There is a genetic component to having a completely black coat and your cat will need the ‘black cat gene’ to be black all over. In addition, to keep a black coat dark and in ideal condition he or she will also require a good amount of the amino acid Tyrosine. Tyrosine is required for the creation of eumelanin, the pigment that makes your cat’s fur black. A sign of a tyrosine deficiency in cats isdiscolourationof the coat, turning the fur from black to a rusty reddish/orangecolour. It commonly starts with the fur changing colour pigmentation at the tips.

There are other potential reasons that a black cat’s coat may change colour and turn to a red/brown colour. However, most issues for a cat’s coat to change to a ginger-brown colour are still related to a deficiency in tyrosine which is caused by either a lack of animal protein nutrition (meat or fish) in a healthy diet or a problem with the cat metabolising or absorbing tyrosine even if it is readily available.

Tyrosine deficiency in cats

Tyrosine is an amino acid. Amino acids are the building blocks of proteins. There are 20 known amino acids of which 10 are essential for dogs and 11 are essential for cats. Essential in this instance means that they have to be provided in the diet as the dog or cat cannot produce them in the body.

Two of the 20 known amino acids are phenylalanine and tyrosine. Strictly speaking, cats only need phenylalanine in the diet because they can produce tyrosine from this. However, extra dietary sources of tyrosine can be useful for some cats. Both phenylalanine and tyrosine are found in animal products such as meat and fish. Interestingly, rice is one grain that contains good levels of tyrosine but with cats being carnivores and able to digest animal protein more efficiently than carbohydrate, meat or fish are still the best dietary sources.

Tyrosine has many roles in the body including being an important component of neurotransmitters in the brain and thyroid hormones. However, it also helps to produce melanin which is the pigment responsible for hair colour. Therefore, cats with a tyrosine deficiency have difficulty producing melanin which causes a black cat to turn a reddish brown colour (this is also known as “rusting”).

Copper deficiency in a cat’s diet

Although it’s not common, a deficiency of the mineral copper can cause depigmentation of coloured coats, causing a black cat’s coat to turn a brown colour. This is because copper is required to turn the amino acid tyrosine to the pigment melanin. Copper has many other roles including being a component of several enzymes as well as being necessary for the normal absorption and transport of iron. Dietary sources of copper include liver and some grains, however pet foods are usually supplemented with copper to ensure pets get everything they need.

Other conditions that can cause discoloration of a cat’s coat

Certain health conditions that interfere with the metabolism of tyrosine may also cause a black coat to turn brown. For example, liver disease. This is because Phenylalanine is converted to tyrosine in the liver. Thyroid and kidney problems have also been implicated as a cause for a change in coat colour.

Over-exposure to sunshine

There are anecdotal reports stating that too much sunshine can turn a black cat brown. However, there does not seem to be any research to back up these claims.

And finally…

As carnivores, cats must derive their energy and nutrients from a diet exclusively or mainly from animal tissue (meat). Apart from tyrosine, they also require meat as a source of many other essential amino acids including taurine, arginine, cysteine and methionine. If you are concerned that your black cat is turning a reddish brown colour* the first and most simple way to resolve this may be to choose a diet with a higher meat content. Check the back of food packets, pouches and tins and remember - a higher meat content is usually tastier and is more suited to the natural physiology of our feline friends.

*If your cat has a concurrent disease such as liver, kidney or thyroid problems you should discuss any change of diet with your veterinary surgeon before switching to a higher meat diet.

References:

Cats require more dietary phenylalanine or tyrosine for melanin deposition in hair than for maximal growth. J Nutr. 2002 Jul;132(7):2037-42.

What is T4? How is the T4 Test Used to Diagnose Hyperthyroidism in my Cat?

Fascetti A.J, Delaney S.J (2012) Applied Veterinary Clinical Nutrition, Wiley-Blackwell.

Linda P. Case, Leighann Daristotle, Michael G. Hayek, Melody Foess Raasch (2011)Canine and Feline Nutrition: A Resource for Companion Animal Professionals, 3rd edn., : Mosby.

The above article first appeared in the Vet’s Kitchen newsletter, October 2016.  My grateful thanks to Chris at Vet’s Kitchen for giving me permission to use this article on the Daily Mews website.