How to “Scrapie-proof” your flock by using genetically resistant rams:

The primary gene that determines whether sheep are susceptible to scrapie (can easily get scrapie), or whether they are resistant (almost never become infected with scrapie) is a gene that consists of a pair of factors usually designated as “R” and “Q”.  “R” is the gene most resistant to scrapie, and “Q” is most susceptible.  So sheep that are “RR” are very resistant, and there have been no known cases of scrapie in “RR” sheep in the U.S.  Sheep that are “QQ” are the most susceptible to scrapie, and almost all known cases of scrapie have been in “QQ” sheep.  Sheep that are “QR” are usually resistant to scrapie; there have been only nine known cases of scrapie in “QR” sheep in the U.S. (with these, another genetic factor comes into play, but we will stick to the basics for the purpose of this article).  Genetic resistance to scrapie has not been proven in goats, and all goats are thought to be susceptible.

In the first example, the ewe and the ram are both “QR”. The square shows all the possible outcomes of the offspring: 50% will be “QR”, 25% will be “RR”, and 25% will be “QQ”. This means that even with parents that are usually resistant to scrapie, one quarter of the offspring born to this pairing would be susceptible to scrapie.

In the second case, using the same “QR” ram on a ewe that is “QQ”, it’s even worse, with half of the offspring being “QQ”.

But in the third case, using an “RR” ram, it is impossible to get any
“QQ” offspring, even out of a “QQ” ewe.  This is how you can “scrapie-proof” your flock if you are saving back your own replacement ewes; by using only RR rams.  Over time as the old “QQs” are culled and all replacements are “QR” or “RR”, your chances of having a positive scrapie diagnosis in your flock shrinks down to zero.  If you buy replacements, look for a flock that uses only “RR” rams.

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