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How is coat colour determined ?

15 May 2023

As you have observed, puppies or kittens with very different coats can be born in the same litter. Some are plain, some are spotted or mottled, while others may be bi- or tricoloured. But where do these differences come from and how is the coat colour determined ?

To answer these questions, we need to understand how hair is made and how it grows in dogs and cats.

Hair is produced inside the hair follicle, which looks like a small sac of epidermis invaginated in the dermis.

Surrounding the hair follicle are structures important for hair growth and maintenance, such as skin glands and hair follicle muscles, as well as an area called the dermal papilla, which is highly vascularised and responsible for providing the nutrients and oxygen needed to produce new cells.

The lower part of the hair follicle bulges into a bulb that contains the matrix. The matrix is composed of cells that are constantly renewing themselves. Among them are mainly the keratinocytes, which produce keratin. As the hair grows, the keratinocytes are gradually pulled upwards. They stop multiplying, but continue to produce keratin. When the hair emerges from the surface of the skin, it is composed mainly of “dead” keratinocytes filled with keratin.

The cells that produce pigment (the melanocytes) are also in the matrix. But the melanocytes are not transported along the shaft. The pigments they produce are transferred to the keratinocytes, which carry them along with them as the hair grows.

The two main pigments are pheomelanin, which colours the hair from yellow to red, and melanin, which gives it black or brown. In the absence of any pigment, the hair remains white.

Pigments give the hair colour, but what decides which pigments are used ? Genetics.

During fertilisation, the genes of the father and mother are combined. Many physical characteristics are thus inherited from both parents, including hair colour, patterns, and the distribution of different coloured spots.

There are also genes that control the density and length of the coat, which can influence colour perception. So an animal with a dense coat will appear darker than one with a sparse coat.

So it’s all genetically determined ? Not quite.

The environment and deficiencies in essential nutrients can influence the quality of the coat and change its colour, as can autoimmune diseases or certain hormonal disorders. Age is also a factor: older dogs often have a whiter coat because melanin production gradually decreases, especially in the muzzle area.

Finally, seasonal changes, levels of sun exposure, diet quality, and living conditions can all affect coat colour and texture.

In summary, variations in pattern and colour of the coat of animals are the result of a complex combination of genetic, hormonal, and environmental factors, and can lead to large differences within members of the same species and litter.

Bibliography

Cummings school of veterinary medicine Tufts University: Why did my pet’s black hair coat turn red?

Demato veto, knowing the skin : thematic sheet dedicated to the structure of the skin on this veterinary dermatology site

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The importance of diet for skin and coat quality in dogs and cats

The importance of diet for skin and coat quality in dogs and cats

The skin is the body's largest organ, representing between 12% and 24% of the animal's weight, and its surface area in a dog weighing around thirty kilograms is close to one square meter. It's hardly surprising, then, that the quality and quantity of the dog's diet can have an impact on this organ, and in the event of a deficiency can lead to problems that go far beyond a simple visual appearance.  

Key nutrients for healthy skin and coat

Among the macro-nutrients, proteins play a crucial role. They provide amino acids, including sulphur amino acids, which are essential for the structure of the skin and coat. These are the main components of collagen, which gives the skin its suppleness and resistance, and of keratin, which plays a part in the effectiveness of the skin barrier. Lipids are also important; they make up the bulk of cell membranes and, in the skin, contribute significantly to the effectiveness of the cutaneous barrier. Among lipids, omega-3 and omega-6 fatty acids help maintain healthy skin, modulate inflammatory mechanisms and promote a shiny, soft coat.  Vitamins and minerals are also involved. Vitamin A is necessary for cell renewal, as is vitamin D, which also plays a part in the skin's natural defences. Vitamin E acts as an antioxidant, while B vitamins and biotin are essential co-factors in the synthesis of various skin elements such as ceramides, keratin and collagen. Among the minerals, zinc is involved in synthesis, protection against free radicals and immune defence mechanisms.    

Disorders linked to inadequate nutrition

Inadequate or poor-quality food can lead to skin problems in our pets. A deficiency in essential fatty acids leads to dry, flaky skin, a dull coat and brittle hair. When it's the vitamins and minerals that are in short supply, synthesis is affected, the skin barrier can be less effective and the breeding ground for infections and inflammations that can lead to itching. On the other hand, these nutritional benefits can be used to compensate for individual sensitivities and improve the quality of the skin and coat in the event of dermatological disorders or diseases.    

Conclusion

The quality of a dog's skin and the beauty of its coat are directly influenced by the quality of its diet. However, some dogs and cats have increased needs, and it is therefore necessary to provide them with greater quantities of useful nutrients. This is particularly true in the case of certain dermatological disorders, to help compensate for imbalances and accompany the medical treatments prescribed by your vet. 

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