"My Rottweiler has at times a redish tinge in the black fur. Does this have to do with the feeding and how can it be repaired?"
The fur color is based on the storage of melamine pigments, which are formed by melanocytes, specialized cells in the skin. There are different types of pigments which, due to their different distribution and concentration in the hair, lead to a multitude of different coat colours in dogs. During hair growth, external influences can influence the formation and storage of pigments.
Hair that has already formed can be lightened by ultraviolet sunlight and thus show a reddish discoloration. In general, hair aging also leads to such discoloration. If the hair begins to die off, the tips first change colour, then the entire hair shaft becomes reddish. New hairs after the change of coat are then black again.
Saliva and tear fluid contain so-called porphyrins. They are degradation products of the red blood cells and can discolour the coat just as reddish when they come into contact with it. One sees this frequently with bright dogs in the eye and mouth area, but also with black fur this can be observed with intensive licking of special body places, e.g. the paws.
Certain conditions "out of the body", i.e. systemic influences, can also change the colouring of the fur.
Thus also the nutrition can take influence on the fur color. However, this is only the cause in very rare cases. A copper deficiency, for example, can lead to reddish discoloration of the coat. When using a balanced complete feed, however, this is almost impossible. A secondary deficiency can occur with uncontrolled supplementation of zinc, for example by alleged fur-improving additional products. Such a copper deficiency, however, would be accompanied by further symptoms such as skin lesions and anaemia. Carotene from carrots and other vegetables can also influence the pigmentation of the coat.
Scientific studies in animal nutrition have dealt with this topic in greater depth. As the pigment melanin is formed from the amino acid tyrosine, investigations were carried out into the influence of feeding tyrosine on coat colouring. Here it was shown that a recipe with plenty of tyrosine also led to a deeper black coloration of the hair.
A certain influence of the diet is therefore proven, but the cause of discoloration of the coat is usually elsewhere justified.
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