[Jacob-list] Genetics and Tail Lengths

[Jacobflock at aol.com]

Dear listers -   Picture this; what does a sheep, giraffe  and shepherd and 
zookeeper have in common? They each have 7 cervical vertebrae  (same number 
of neck vertebrae) but differ in caudal (tail)  vertebrae.  Don't let the 
tail wag the dog.
 
Phylogenetically the Jacob's medium tail seems a logical compromise between 
 the primiitive Mouflon roots (3,000BC) and its modern ancestors 
(1600-1800AD)  Ryder 1983, Noble 1913, Elwes 1913.  Werner (1988) suggests some of  
the Jacob's relatives from Scotland and Western Britain have a similar  
mouflonoid medium tail and horns.  Ewart in describing polycerates and  mouflon 
influence focused on horn and skeletal features including the caudal  
vertebrae of Soay's with 13 vertebrae.
 
Genetically, tail length seems to be a highly heritable trait and the  
"average" of the parents tail length (Scobie and OConnell).  Tail length is  not 
apparently heritable in the sense of dominant length but influenced by 
breed  tendency.   Tail length (vertebrae, skin and fiber) is controlled by a  
number of genes and each element contributes to its "apparent" length.  The  
genes that control the number of caudal vertebrae are controlled by a set of 
 genes that regulates cell life, growth, structure and death ... call them 
Hox  genes.  In a sense, Hox genes send messages to make caudal vertebrae at 
 certain places and then says ... that's a good length, width, ligament  
attachments, etc and that's enough of those.  Genes also control the length  
of the caudal vertebrae.  There are genes that control wide and narrow bone  
structure, fat, muscles etc.  I believe it was Livy (Junior or Senior  HS 
Latin) who described Roman ag practices and a ag sho that featured a  sheep 
with a tail so long that it needed a wagon to keep it off the  ground.
 
A sheep can have from 3 - 24 caudal vertebrae and these are rather  breed 
specific: Mouflon 11 (Boylan), Finn Landrace 24, Cheviot 24, Orkney and  
Shetland 13 (Ryder) .... based on twelve Xrays of Jacob's tails in 2004,  and 
some additional tails xrayed in 2005, Jacobs have 16 caudal vertebrae  
including the 2 at the pelvis.  X-ray of the vertebrae is preferred  to palpating 
the vertebrae ... it's accurate and the length of the  vertebrae can be 
measured.   
 
Most breeders would not stop to xray vertebrae and count bones.  So  the 
standard says the tail is about hock length; what you can usually see.   If a 
tail is unusually long or short (such that a question might arise)an option  
is presented: (a) dock or (b) leave it ... and count and measure the  
vertebrae.  
 
Warwick (TexasA&M) did some work to shorten Rambouillet tails and  within a 
113 breeding group came up with a ratio of tail length to body length  
(including the tail).  The number of tail vertebrae (which he counted) and  
compared it to his "tail ratio" had a correlation of .84; pretty strong.
 
We too have crossed some pedigreed pure bred Jacob ewes, in our case,  with 
a pure bred pedigreed StCroix ram.  The result first  generation cross 
offspring appears to have (a)  a "short tail"  and (b) a "variable width tail" 
i.e., perhaps the first 5 vertebrae are one  width, the terminal four or five 
are a narrower width.  This  initial observation will have to be tested by 
xray as were the number of  Jacob caudal vertebrae
 
As some old breeders remember, there is a wry end to this tale.  A  
congenital defect, wry tail, has been reported in Jacobs.  A "dead tail" (a  tail 
that just hangs and does not move) is also a defect.  
 
Fred Horak
St. Jude's Farm
1165 E. Lucas Rd.
Lucas, TX 75002
 
 
In a message dated 5/30/2012 1:02:34 P.M. Central Daylight Time,  
farmgirlarts at triad.rr.com writes:

For  those of you who have crossed any short tailed sheep (i.e., Shetlands, 
 Icelandics, Finns) with Jacobs or other breeds:
I'm wondering if long tail  is dominant. I have a 1/4 Jacob, 3/4 Icelandic 
ewe that has a long  tail.

Laura
--

Laura C  Frazier
http://www.farmgirlarts.com
http://www.etsy.com/shop/farmgirlarts/

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