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Metallic Sheen as Observed in Individuals of the Akhal-Teke Breed

By Danielle Westfall, Zoology major, Ohio Wesleyan University

Advisor, Dr. Laura Tuhela-Reuning

This project was first suggested by a project of a similar nature involving cat fur from the Bengal domestic cat.� The surface structure of the Bengal cat affected the degree of glitter exhibited, and several Akhal-Teke breeders wondered if a similar glitter effect in their horses was related to the surface structure of the horse hair.� They sent samples to Ohio Wesleyan University in the hopes of discovering if the metallic hair had different structural features than the nonmetallic hair.

���������������� For years, Akhal-Teke owners have marveled over the metallic quality of the coats of some of their horses.� In fact, individuals such as Fara Shimbo, author of �The Akhal-Teke Glow� and Dr. Philip Sponenberg have studied the hair structure of these �glowing hairs�.� They studied the inner features of the hair using light microscopy.� My study picks up at analyzing the surface morphology of the hair using the scanning electron microscope (SEM).� I believe this is the first study to employ the SEM to examine the surface morphology of metallic Akhal-Teke hair.

���������������� In researching the subject, some may find it interesting to note that other breeds of horses also exhibit a similar glow.� Namely, horses carrying the Champagne gene, in breeds such as the Quarter Horse, Thoroughbred, Saddlebred, and Tennessee Walking Horse, have been known to have a metallic sheen to their coat.� The sheen is not the same, however, because the gene lightens the coat, eyes, skin, and the sheen is less strong than in the Akhal-Teke.� So this gene not only effects the coat but the entire pigmentation of the horse.� The Turkoman strain effects only the coat - not to change the color, but to make it glow.� I will attempt to explain what is unique about the hair of this horse and suggest how the structure of the hair contributes to such a phenomenon.�

figure 1

 

SEM photograph of Akhal-Teke hair with characteristic scaling of metallic hairs.� Note the straight, flat, smooth edges of the scales.

 

���������������� Not to get too technical, but I will give you the bare bones of my methodology for examining the hair.� For a more detailed description, you can visit my website, which includes the entire technique, at:� www.owu.edu/~sem/methods.html.� First, I examined the hairs longitudinally by cutting them down to fit on small aluminum stubs that could be placed in the SEM viewing chamber.� A scanning electron microscope works by shooting a beam of electrons at the sample and recording the pattern of how those electrons bounce off the sample to create a black and white image.� Thus the samples had to be coated with a thin layer of gold first so they would conduct electrons.� The gold layer is so thin, however, that it has no effect on the surface features of the hair.� Photos were taken of all the samples.� Then I analyzed the hairs in cross-section by cutting them into pieces under liquid nitrogen.� Freezing the hairs before cutting them kept them intact.� I then stood them up in carbon paste so I could observe the inner structure of the hair in cross section with the SEM.

���������������� The hair structure differed as one progressed from the root to the tip.� The root showed fine scaling or none at all.� Then towards the middle section, scales were short and fairly flat, sometimes with an irregular arrangement.� The tip of the hair showed longer scales with �choppy� edges, but a regular pattern.� Thus, the most variation was seen in the middle of the hair, which became the focus of the study.� After analyzing the hairs, I categorized them into two classes.� In the longitudinal investigation, two classes were evident based on the pattern of scaling and the shape of individual scales.� Class I exhibited a regularly spaced arrangement of scales, known as coronal.� The scales also had straight, flat, smooth edges and looked somewhat like a stepladder (see figure 1). Scales of Class II

figure 2

SEM photograph of Akhal-Teke hair with characteristic scaling of nonmetallic hairs.� Note the serrated, choppy, jagged edges of the scales.

 

hairs, however, were in an irregular pattern, called imbricate.� Scales of this class had choppy or serrated edges and resembled tree bark� (see figure 2).� I also examined the hair of several other breeds such as the Quarter Horse and Thoroughbred.� Hair from these horses had very choppy and irregularly shaped scales that looked like fringe in the mid section.� There was a high correlation between metallic hairs and Class I and non-metallic hairs and Class II.� Thus, I concluded that the pattern and shape of cuticular scales must be related to the metallic properties of the hair.� The more regular and flat the cuticle edges, the more glowing the hair.� There are many possibilities as to how the cuticle pattern may affect the metallic properties of the hair.� Perhaps more smooth scales are better able to focus and concentrate refracted light.� Or maybe the thicker scales of nonmetallic horses are more easily peeled away from the shaft and consequently are more likely to become damaged and �fringed�.

���������������� The cross-sectional analysis also resulted in two distinctions of hair.� Class A hairs had a larger medulla than cortex.� Also, there was more variation in cortex size within Class A.� Hairs belonging to Class B were just the opposite.�

 

SEM photograph of cross-section of Class A Akhal-Teke hair with characteristic inner structure of metallic hair.� Note the large medulla relative to the inner cortex.

 

SEM photograph of cross-section of Class B Akhal-Teke hair with characteristic inner structure of nonmetallic hair.� Note the larger size of the cortex compared to that in the Class A photo.

 

The cortex was larger than the medulla.� Also, the cortex size was more uniform throughout the representatives of this class.� After categorizing� the images, I matched the amount of glow with the class of hair.� The initial grouping was done blindly so as not to bias the results.� After degrees of metallic nature were assigned, I found that most of the metallic hair fell into Class A while for the most part, non-metallic hairs were of a Class B nature.� Thus, there was a strong correlation between the cortex/medulla size and the metallic nature of the hair.� In this procedure, I was not able to distinguish cuticle layers, as this layer was too fine to detect.� Since the hair is so fine and silky, it has a very small cuticle, which may account for the large amount of light refracting through the hair to produce the glow.

���������������� There are many possibilities for the further study of the metallic properties of hair.� For example, it would be useful to trace the hereditary nature of the metallic trait in order to determine what type of gene carries the property.� Also, investigation of the Champagne gene and hair of the champagne color that also exhibit this metallic sheen would be interesting.� A comparison could be made between champagne colored metallic hairs and Akhal-Teke metallic hairs, since they represent the same metallic property, but have different origins and different accompanying characteristics.

This article was first printed in the ATQ in July of 1999.� It has been suggested that I reprint this for those of you that haven�t had a chance to read it.