Copying and pasting from a thread on COTH, "How does Paprika actually work to darken coats?" first post on page 2 -
http://www.chronofhorse.com/forum/showt ... ing&page=2
there are basically two pigments in the hair of the horse Eumelanin which is black and phaeomelanin which is red or no melanin which is white. The pigments occur in microscopic granules and are laid down between the strands of Keratin which make up the hairshaft.
The pigment granules are produced at the base of the hairshaft and can be laid down in the shaft in various different patterns (genetically controlled) .
They can be all around the hair shaft, or just on one side (dilution gene) or just on the inner surface of the shaft (double dilution gene).
Once laid down and the hair has grown out of the root bed, they cannot be added too, but they can be destroyed or altered by the action of chemicals or sunlight or both.
The biochemical pathway which produces both pigments involves an enzyme that uses copper ions as an electron acceptor. Thus for the pigments to be produced fully there needs to be copper present in the cell.
If the horse (or cow) is short of copper then the enzyme can't do it;s job and the pigments are produced slowly if at all and sometimes in a different form.
So to ensure that the animal gets it's full dose of pigment synthsized you need to ensure a supply of copper in the diet.
Paprika is rich in copper flavenoids, especially the Hungarian paprika.
Thus as long as you feed a supplement rich in copper the hairs will get their full dose of pigment. BUT this only happens when the hairs are being produced as they grow, once they are grown, you cannot add any more pigment, you can only either lose it to the action of sunlight and or chemicals.
So once the hair has grown you can improve the texture of the hair (more on that later) but not the content. You can add pigment to the outer layers as in dyeing, but not to the inner hair shaft.
Part of the appearance of the color is not only where in the shaft the pigment granules lie but the refractive index of the scales that coat the outside of the hair shaft ( I warned you that there would be physics involved).
Whene the hair is new and young the scales have a good supply of sebum, the oil which coats them and they have a high refractive index, the light gets bounced around within the hair shaft and the hairs appear darker and shinier.
As the hairs age they lose the sebum, and the scales begin to peel away and the hair appears less shiny and lighter.
So to help the hair keep it's refractive index you can
a) give the horse a high fat diet which makes the little sebacous glands at the base of the hair produce more sebum, which coats the hairs and they appear darker and shinier (hence why Platinum Performance, a high fat supplement based on flax seed causes a darker coat).
Or B) apply a conditioner with oils in it to the hairshaft. This will also cause the little scales to lie down flat and improve the refractive index.
You can also apply a coating of conditioner with little tiny reflective scales in it these tiny scales add to the refractive index and make the hair shinier.
But anything applied to the outside of the hair shaft is going to be temporary at best.
Things on the inside last a bit longer.
But the bottom line is to make a hair coat darker and shinier use a mix of copper and fat. The fat has an immediate effect the copper when the next coat change occurs.
BTW if you eat a lot of Hungarian paprika your skin will get a darker shinier color as well, that's what the feed through fake tans are based on.
Your hair will grow darker as well, but you'll see it first in the skin.
