why does the hair of animals not turn grey or change colour on ageing, unlike those of humans?

Answer 1

Hairs differ in respect of hardness and softness, length and shortness, straightness and curliness, abundance and scantiness and in addition to all these qualities, in their colour, whiteness and blackness and the intermediate shades also according to age, as the animals are young or growing old.
Human beings also go grey or change in colour on the head as they grow old but this is not visible in practically any other animal, though it is so in the horse than others.
Each part of the body has its own specific heat. If the heat is inadequate, the part looses its efficiency, and destruction or disease results.
The hair in man has naturally little heat and too much moisture enters it and its own proper heat is unable to concoct the moisture and so it is decayed by the heat in the outside air. All decay is caused by heat-not the innate heat but external heat.
And as there is decay of water, of each, and all such material bodies, so there is also of the earthy vapour, for instance, which is called mould.
Thus the liquid nutrient in the hair also decays because it is not concocted and what is called greyness results, which can occur visibly in horses more than in other animals.
Usually hair change occurs according to the nature of the skin, that is, thickness and due to heat and cold factors of parts of the body. With the advance of years of life, all animals are alike in some points, but are opposed in others as in the case of the colour of the hair. Some do not grow grey visibly in old age, while man is subject to this more than any other animal.

Answer 2

Actually ... some animals do lose the pigment in their hair/fur on aging. Most dogs will get grey or white hair one their snouts as the get older. Horses do, too ... the old grey mare just ain't what she used to be.

The color change comes about when the hair follicle stops producing the pigment (color) that it does when we are younger.

Answer 3

It does change! All of our dogs and our cats had changes in their fur as they aged. The dogs definitely went grey, not as much as humans, but a noticeable change. The cats have also changed, but not as much. Also, their whiskers and eyebrows have grown much longer as they have gotten older. Almost like an old man's eyebrows... long strands totally out of control! LOL