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Horse Hair Under a Microscope: A descriptive report

There are many variations among horses in hair colour - especially the colours we register. The particular hue (colour shade), value (lightness or darkness), and intensity (saturation) of a specimen are enhanced through microscopy so that even subtle differences may be distinguished. The range in colour of a particular hair sample, presence and placement of certain hair structures and the variations in colour that exist along the length of hairs are important comparison characteristics.

In this diagram the medulla is shown fragmented and very narrow ( as it appears in human hair). The medulla is much wider in horse hair as you will see.

A diagram of a hair shaft

Hair Structures


A hair shaft is similar to a drinking straw in that it has a hollow core-that is the very dark centre, (sometimes looks like bubbles). Surrounding this core (the medulla) is the pigment, this gives the shaft its' colour.

When the pigment is darker/deeper on one side than the other (I have to turn each hair to make sure I don't miss it) that will indicate dun. But a true dun shaft will present with this colour loading (apart from the tip and follicle) to one side all the way along the shaft.

Looking at the differences between buckskin and dun has been a high priority as with some of the darker horses physical classification has been very difficult. With the aid of the microscope to compliment physical classification in hard cases the decision can be lot easier to make determining the correct colour.

In addition to the research of buckskins and duns, I have done studies and picture files on palomino, cremello and most of the non-dilute colours (bay, black chestnut etc) as well as champagnes and some other strange ones including donkey and soon zebra…when the hairs arrive! Below a mid shaft from a grey donkey…they actually can have grey hair not a mixture as horses do, also note the pigment loading to one side. (Explained further on).

Gray Donkey hair under a microscope showing pigment loading to one side



There are differences between all the colours…some very marked and some quite subtle. One definite in my research has been that this is very much “what you see is what you get”. For instance if I test hair from a grey, they will present as a mixture of white hairs and some darker hairs e.g.; black or sometimes chestnut. I will not be able to tell what colour “the grey” was when it was a foal-only what it is now. If I test blue roan, the hair will present as white hairs and black hairs (as below) - a red roan will present also as a mixture of white hair and chestnut hair etc.

Black (Blue) Roan Hair under a microscope showing a mixture of black and white hair that give the horse it's "blue" coloringBlack (“blue”) Roan-mixture of black and white hairs.


The cremellos' medulla can be one sided (why I don't know may be because the hair is so fine and soft and maybe not as structurally strong as other colours ).

Cremello Horse Hair Cremello Horse Hair

A white cremello (left) and a cream cremello (right).

A clear tip and follicle with a very definite darker end before the tip will hint strongly at buckskin but this colour has been the hardest to determine so I recommend definitely DNA testing these horses…Although a smoky black that is almost impossible to tell by the eye will show well under the microscope as will a black dun. Below shows photos of a black dun shaft, showing the clear tip and follicle and pigment loading to one side that is consistent.

Black Dun Hair Shaft Follicle end.

Mid shaft. Tip.

Black Dun Hair Shaft Under A Microscope

Below mid shaft, near the tip and the tip (follicle was clear) of a buckskin.(this particular one a very classic and easy one to determine-a golden buckskin).

Black Dun Hair Under a Microscope showing the tip of the hair shaft

A light iridescent chestnut shows up very much like a palomino but determining these two shouldn't be a problem with physical classification.

Buckskin hair under a microscope mid shaft
Buckskin Hair under a microscope near the tip

There is pigment loading to one side (not consistent though) in a very iridescent copper bay I tested recently (also a pure Andalusian but they also do have a historical connection with the Sorria (sp) that only comes in dun.). Or it could be the copper iridescence of the hairs.

The tip of a buckskin hair under a microscope

Iridescent chesnut hair under a miscroscope Iridescent Chestnut Hairs under a microscopic  showing a bit of pigment loading


Bay Hair Under a Microscope showing lack of medulla and pigmented tipNote the lack of medulla(just a few “bubbles”) and the pigmented tip of a bay-non dilute factor.


I am awaiting hairs from Spain from a pure Sorria mare and stallion. Other Pure Spanish bays have presented “almost normally”


The champagnes are very similar to the palominos but with varying shades of pigment depending on their colour. Their medulla index, ( the width of the medulla compared to the width of the whole shaft and expressed as a fraction) is very low and they contain a large number of thicker pigment strands that are responsible for the amazing metallic iridescence.

The iridescence in any colour seems to be caused by these “strands” As light reflects quite strongly off these “strands” and in a different direction to the normal reflection off the shaft. (That is why when you are viewing a horse with this that it only shows at “certain angles”.).
Iridescent Palomino Hair under a microscope note the orange coloured strands Palomino horse hair under a microscope less iridescent palomino of medium color

On the left is a dark very iridescent palomino. Note the orange coloured strands. On the right a less iridescent palomino (of medium colour).


Most Appaloosa white has a wider medulla than the cremello and the cuticle (outer most layer) seems” rougher” than cremello. Appaloosa White Hair Under a Microscope with wider medulla than the cremello and "rougher" outer cuticleAppaloosa white (chestnut shaft from a spot partially viewed)




Below is a sample of dun hair; the follicle is clear as is the very end of the tip. The medulla (core) has a width at its’ widest of 2/3. The pigment is consistently loaded to one side, until the tip. Whether the horse is a red dun, palomino dun, buckskin dun, black dun, etc these “factors” remain the same - although the lighter the colour the less the contrast of the light and dark of course.

Dun Hair under a Microscope follicle Dun Hair Under a Microscope showing pigment loading above the follicle Dun Hair under a microscope again showing pigment loading 2/3 along the shaft

Clear follicle. Above the follicle. 2/3 along the shaft.

Dun Hair Under a Microscope close to the tip Dun hair under a microscope tip showing a near clear tip

Close to the tip. The tip.

When you look at a true dun horse they don't seem to shine as well as a non dun, a dun factor in itself, that is because the darker pigment is located closer to the skin (this would reflect more light, eg shine) and the lighter side up ...the side you look at. (Light will travel through more -refract...less shine). Light coloured horses will shine more than duns as they have a number of thicker pigment strands in the shaft that the light can reflect off.


Certain shades of bay can present like buckskin, especially the lighter shades so DNA testing is a must for these. The darker bays have a pigmented tip so are fairly basic,

as are most blacks - these will have a pigmented tip and most often follicle.

Black horse hair under a microscope showing pigmented follicle Black Horse hair under a microscope showing pigmented tip

Black follicle-pigmented Black tip-pigmented


Dyed or bleached hair has no medulla at all and has a false appearance. As below;

Dyed horse hair under a microscope showing a "false" appearance


The easiest colours therefore to determine with this work are dun, black dun, black buckskin, champagne, all the “whites” and bleached/dyed hair.

Colours such as brown bay looking buckskins and liver chestnuts etc prove to be difficult to determine at the moment but with further research hopefully this will become clearer.