[Jacob-list] genetic defect - Suffolk flock

[Jacobflock at aol.com]

Mary, Fred Horak here responding to your Suffolk genetic defect question and 
perhaps some leads.  

First, I am not a vet or expert on spider syndrome (SS) but do try to stay in 
touch with genetic defects because most defects are recessive and can 
threaten conservation of the Jacob...perhaps not the breed but certain lines. 
 

Some of the TX Suffolk breeders jump immediately to SS for any skeletal 
deformity.  There are several deformities, common "look alikes", that can 
occur in any breed. (1) bent leg which is sub-lethal and (2) and AGH lambs 
which have severly twisted spines and most or all of the joints are "frozen" 
and immobile and die before or at birth. SS is very specific and the 
"classis" symptoms are the "S" curve, severely humped "camel back", long 
necks and legs that have the "spider" look.

Don't guess at the SS symptom.  If you can get somebody to see the lambs or 
have your friend compare these to pictures on the Web, that would be a plus.

Second, my knowledge of genetics was gained from Mendel...I picked peas, ate 
most of them.  However, the operative genetics seem to be those associated 
with all defects; a recessive gene.  Most skeletal deformities are single 
autosomal recessives...sire and dam are both carriers.  The probability of 
your Suffolk being a carrier with a proven carrier is rather high.  In such a 
case you should expect a 50% good - 50% defect result from such a breeding in 
the first generation (F1).  For each successive generation you can expect to 
see one half the (F1).  That is F2 would be 25%, F3 would be 12.5%...etc.  A 
recessive gene always hangs around waiting to be expressed.

I would suggest that you closely look at the pedigrees of these Suffolks. The 
ram you had a few years ago who threw the SS lamb; he was a carrier, the ewe 
was a carrier.  Did you keep any of these lambs and they are now in your ewe 
flock?   They are carriers.  The ram that you got from the breeder going out 
of business (same ram  or different ram?) who is throwing SS or SS "look 
alikes"; he is a carrier of the defect as well as the dams.  Any surviving 
lambs ("look okays") that are sibs of "not okays" are probably also carriers. 
 They should be progeny tested.  

The "progeny" of a breeding tell you the genetic content of the parent.  One 
"bad progeny" means the parents must be examined closely.  For many years the 
SS lamb was bonked behind the barn and everyone kept quiet.  Affected 
carriers went to sale barns...some to slaughter, some to other breeders.   
Some of these breeders took the "best of show" from flock to flock, producing 
more carriers.  It devastated the Suffolk breeders in the 80's and 90's until 
one or two breeders reported the problem and some corrective breeding 
programs with SS free rams could be put in place.  I noticed that you said 
the 3 "rather pure" Suffolks twinned without problems; pedigrees suggesting 
"crossing" might confirm your recessive pure Suffolk carriers.

With the incidence of defects you are experiencing, I would try to find some 
support from the Suffolk Breed Assoc or a nearby Vet school that handles 
sheep problems. I am not an expert but I suspect you have a valuable flock 
for identifying defects.

Your experience is valuable for any breeder and I thank you for sharing it.  
Personally it has reinforced my closer observation of problems that may have 
a heritability basis.  Thanks.  Fred Horak