[Jacob-list] Graying & Ticking / Environment

[Jacobflock at aol.com]

In a message dated 4/11/2003 6:24:04 AM Central Standard Time, 
patchworkfibers at alltel.net writes:

> Is there an environmental effect on freckling and/or ticking?  For instance, 
> many 
> sheep around here have faces that get progressively darker (we used to have 
> sunshine around here!) but do not exhibit any progressive ticking on the 
> body.  

I suspect that this is a classic(?) geneticxenvironment question.  It is my 
casual observation that the back of the sheep (dorsal line) seems to produce  
freckles as a reaction to the sun's UV rays; perhaps anthropomorphizing my 
experience in summer (my skin darkens and freckles appear on exposed areas).  
I notice a small increase in the number and size on the back itself and few 
if any on the side; and this observation is primarily associated with 
shearing time (I start in March  but still have about 50 to shear).  This may 
be an eroneous observation because I also seem to notice increased number (or 
is it only size from stretching?) of "black skin" patches on the sides during 
late pregnancy.

I think that the skin's reaction to UV would be to produce more melanin; thus 
increasing the density, number and size of the skin freckles.  It would be 
difficult to actually measure the effect since a control and subject would 
have to be kept "constant" except for exposure to the sun.  The effect of UV 
on the fiber is, to some extent, the reverse, i.e., UV tends to breakdown the 
"black" eumelanin.

       Also some > sheep will show a blanket sort of ticking pattern that is 
> predominately along the spine.  Is this possibly something that is either a 
> result of the sun or something 
> that is accelerated by the sun?
> 
> What about so-called age spots?  Would these be caused by the same factors 
> as 
> ticking or are they genuinely just a sign of age?
> 

My "age spot" (note my use of the singular to represent the first age spot 
that occurs at 50 years of age) is on the surface of the skin.   I think a 
comparable "age spot", if a sheep would have same, would appear about age 20 
on a sheep, all other things being equal.  

> For clarity - I am using the term "ticking" to refer to a progressive 
> darkening of 
> the fleece, not the "freckling" that is apparent at birth.
> 

I think that is the correct general understanding of those terms as used by 
COGNOSAG .... which is something like the Committee on Genetic Nomenclature  
of Sheep and Goats.  

Fred Horak
St. Jude's Farm
Lucas, TX
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