[Jacob-list] grayed wool to black s/p injury

[Jacobflock at aol.com]

In a message dated 10/16/2004 8:08:33 PM Central Standard Time, 
shepherdofspots at yahoo.com writes:

> I have been involved with horses for years. When a
> horse with dark fur gets a cut, one must cover the
> healing area with vaseline (or cut heal substance);
> otherwise, the hair that grows back is WHITE!
> 

There are several considerations: the hair "color" of the horse, the nature 
of the cut and the remedial action (if any).  Also consider the branding of a 
horse; freeze brands are generally white, heat brands are generally black.  
Saddle sores, breast collars and bridles (a reuslt of not "fiting" tack to the 
horse) results in white hair.


> This is neat - with a Jacob sheep the cut area grown
> back BLACK!
> 
> Fred, is there a genetic reason for this?
> 

Perhaaps one can consider both a genetic and biologic basis.  Maybe the 
review could be considered in the following order.  First, one can consider the 
"genetic color" of the animal.  Horses and sheep have the same two basic options: 
black or red.  Horses have a complication with the interaction pf point and 
body color and is not going to add materially to the color of Jacob sheep.  
Second, one might consider the biology of fiber growth.

By definition, the Jacob sheep is a dominant black.  Some graying is simply a 
few black fibers "mixed" in with the white piebald marking, sometimes it may 
be dust or dirt attracted by lanolin; sometimes it may be the effect of 
ticking or graying.  A clip of clean fiber and separation of the fibers into "piles" 
and examination under 400x or more helps identify the situation.  Fading can 
also beinduced by ultra violet light particularly in the lower B range which 
is damaging to fiber.

There are reports from some breeders of the Jacob color turning from apparent 
"white" to "gray" and "black" to "gray".   (1) The turning of white to grey 
may be the result of the Ticking gene.  Ticking is dominant to its absence and 
varies by number and extent on the body.  Ticking "grows" from a few with a 
grey appearance to such dense ticking that the fleece appears solid black.  
Genetic "ticking" is often described as "freckles" or "pigmented multiple 
spotting". (2) The turmning of black to gray is a result of the Graying gene which 
exhibits the premature loss of black.  The graying gene may be the consequence of 
a poor eumelanin producing melanocytes. The graying gene is dominant.

Maybe if we consider what black fleece structure it will become clearer.  
Sheep skin has two layers: dermis (inside) and epidermis (outside).  The 
formation of wool, hair and kemp (three distinct fibers) begins in the dermis.  The 
dermis contains follicles (two types: primary and secondary follicles).  Primary 
follicles are large, generally arranged in rows of three, have a sweat gland 
and a muscle and produce hair.  Secondary folicles grow fine fibers; secondary 
follicles are associated with a "surround" primary fibers. Follicles have 
"bulbs" where color is produced.

The black pigment (eumelanin) is produced in the follicle bulb at the 
melanocyte.  Here, eumelanin is a protein formed by the oxidation of tyrosine.  
Eumelanin chains lappear to "pack" more tighly in "black fiber", the chains appear 
broken in "gray" fiber.  Melanin pigment migrates from the melanocytes to 
nearby cells called keratinocytes and is transformed to eumelanin, "pigmented" and 
"bonded" to the fiber (keratin) through an oxidation process.  Melanins bind 
to a rather wide range of compounds and metals; binding poorly with iron, 
binding very well with copper.  Thus diet can have an effect on black pigement 
(iron vs. copper); a reduced ability to convert sufficient copper to produce 
close, packed, chains of eumelanin. 

The observation that black fiber has a larger diameter than white fiber might 
be attributed in part to the packing of the eumelanin inside the thousands(?) 
of micrfobils that comprise one strand of fiber.

Ultra violet light is not very destructive of eumelanin (tyrosine) but there 
will be some damage to tips which may appear to be "brown" or "gray" 
especially in lower latitudes. So, in a sense, one can think of eumelanin as the 
dominant latex paint for the Jacob; the white is the recessive piebald which is a 
"surface on which black paint won't stick".

The fiber for deep wounds, scrapes, cuts etc., would be expected to be 
replaced by the dominant color.  Thus the black fiber regrowth on the Jacob would be 
expected.  What would be of further interest is any transformation of the 
color over time; say three years which is about the time frame to confirm the 
dilution of the eumelanin chains in the fiber and presence of a "graying" gene.


Fred Horak
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