Does Q Stand For Quality?
By John Bare * reprinted in the St Croix Newsletter Vol 4(3) 2007, from June 2007 Sheep Industry News

As a veterinary medical officer with the U.S. Department of Agriculture (USDA), one of the most challenging and least desirable parts of my job is removing scrapie-susceptible sheep (usually QQ sheep) from scrapie-infected flocks. Although it is incredible that we are able to remove scrapie from a flock in as little as two to three weeks while leaving the majority of sheep (QR and RR) in place, it can be an especially stressful situation for the owners.  More than once, when going over the genotype results for their flock, infected flock owners have lamented that some of their best sheep came up QQ. While good ewes are certainly present in the RR and QR genotypes owners will retain, it is easy to focus on the QQ ewes that are potentially infected. Although the genetic-based scrapie flock plans are a far better alternative to the old days (before my time) when entire flocks were removed, having to part with scrapie-infected or potentially infected susceptible sheep is a situation I would never wish on anyone.

Even though the USDA pays compensation quite well for scrapie exposed QQ sheep (far better than most QQ breeding stock sells for), to lose such a chunk of valuable genetic potential in one fell swoop is mind boggling, but what is more mind boggling are the people who are wasting the exact same genetic potential not because they have to but because they choose to (italics added). 

While removing susceptible sheep from scrapie-infected flocks may not be an enjoyable part of my USDA job, as a four-plus generation sheep producer (my other job) getting out and just "talking sheep" with other producers is by far the best part. Many of my visits involve tracing scrapie-exposed sheep and generally end well, with the traced animal found not to be a scrapie-transmission risk to the producers flock. In fact, nothing warms my heart more than finding out the sheep in question is resistant to the scrapie type being traced, as it makes everything more pleasant for everyone.  Unfortunately, during these visits and others, I have started to notice something that does anything but warm my heart. With the availability of private genotyping of sheep, many producers have implemented their own Q gene extermination plans. As a result, I have been seeing a number of RR sheep being retained that are not as high quality as the QQ and even the Q sheep being culled. Many of these RR sheep are excellent, but more are just okay, and a few look like an orangutan swam a couple of laps in their gene pool. At the same time, some producers are noticing remaining QQ and QR sheep are beginning to appear superior to RR sheep. Does Q stand for quality? What the heck is going on here?

What is "going on here" is an observable decrease in the quality of overall characteristics due to incredibly intensive selection of a single characteristic. Other species and breeds have fallen into this trap many times before. Perhaps the best example can be found in many of the dairy cattle breeds. Prior to wide­spread use of artificial insemination (AI), cow improvement occurred relatively slowly, creating an animal that was more balanced regarding other important characteristics such as conformation, reproduction and longevity.  When AI became available, rather than use a wide base of balanced bulls, producers used a small handful of bulls selected almost exclusively for pounds of milk produced per cow. The result was a near disaster; as the gene pool dramatically shrank, milk production did increase, but it became contingent on if her legs didn't go out, if you could get her bred and rebred and if you could keep her alive. In a couple of breeds, rare life-threatening genetic disorders even became common.  Things have changed since then and broader selection criteria are used, but a great deal of damage has been done to the point where some crossbreeding plans are being used in many breeds and some breeds have even opened their books to crossbreds. The blind pursuit of one characteristic led to the near complete loss of other characteristics vital to the end goal.  It doesn't matter if your goals are selecting your sheep for milk, meat, wool, hair coat, hoof color, coat color, eye color or singing voice; over selection for one characteristic, such as scrapie resistance will at best delay your other goals and at worst make them unachievable.

This brings us back to the title of the article, "Does Q stand for Quality?" Thus far I have not seen any compelling research that would indicate sheep being QR or QQ at codon 171 have any advantage regarding productivity. It appears to only be involved with scrapie resistance.  So why does it seem like many QQ and QR sheep are superior to RR sheep? It is because QQ and QR sheep are being selected by a stricter set of criteria than RR sheep. For an example, say a producer decides to make their flock resistant to scrapie, so he or she starts genotyping. The producer finds their ewe flock and lamb crop are about 25% RR, 50% QR and 25% QQ. Some producers at this point may sell all their QQ sheep, and a few might even sell all their QR sheep. If they sell all their QQ sheep, they would eliminate 25% of their genetic base, and if they sell their QR sheep, they would eliminate 75%.

Talk about a shrinking gene pool! Since they need to replace the culled QQ and QR sheep, nearly all RR sheep are retained regardless of quality. Naturally, they want to use an RR ram so they go to a flock that has done the same thing and pick up a ram that is also po­tentially decreased quality. As a result, the average quality of the flock is significantly decreased in just one year.

Expand this trend to the entire breed and we are quickly heading down the path of dairy cattle. Now, not everyone would be so drastic, but would move in the same direction. Many, instead would retain most of their RR sheep, including some sheep they may normally have culled and retain QR and QQ sheep of the highest quality, culling some sheep they normally would have kept. Thus, you can see how QR and QQ sheep would start to appear as superior in such a flock (or breed) since only the best of their kind are being retained. The Q becomes an inadvertent marker of increased quality even though it directly causes no benefit.

The key to avoiding the over-selection trap is to go slowly and select your sheep on a set of balanced criteria of which scrapie resistance is one. I AM IN NO WAY SUGGESSTING PRODUCERS BREED FOR QQ SHEEP! The exact same over-selection problem will happen if one breeds for QQ, except the flock will be more susceptible to scrapie. (Nor am I suggesting that producers who believe their flock may be infected or at high risk for scrapie shouldn't move toward a QR and RR flock).

A better strategy is to minimize the number of scrapie susceptible sheep in your flock with careful breeding to keep your QQ percentage below 25%. A person can think of many ways to accomplish this. Have some great QQ ewes? Don't cull them, just breed them to the best RR ram you can find. Have a lot of RR ewes? Breed them to an exceptional (and probably very affordable) QQ ram. Both of these scenarios will result in 100% QR offspring so you don't have to shell out one dime of genotyping money. Using a QR ram on RR and QR ewes will produce a majority of RR and QR offspring with a smaller number of QQ sheep. This will keep your scrapie susceptibility low, but you may need to do some genotyping. When selecting from your lamb crop, select the sheep you intend to keep or sell as breeding stock. Then genotype only those individuals to determine how they need to be mated to minimize scrapie susceptibility. The ungenotyped animals can be sent to slaughter (no matter what anyone tells you, not all of the sheep produced in your flock will be breeding stock quality, regardless of genotype).

This does carry the risk that if scrapie is traced into your flock, you may have to cull your QQ sheep to clear the infection, but it gives you years to spread their other valuable genetic material across the flock through QR offspring that will stay. Don't forget that culling QQ and QR sheep is what a lot of people have been doing already, even though they don't have to. It is a bit like peeling off your skin to eliminate the risk of skin cancer; it works, but there are complications with the strategy.

Producers also need to keep in mind that the National Scrapie Eradication Program is working, and each year, fewer new scrapie infected flocks are found. About 40% fewer infected flocks were found in 2006 than in 2005, and this trend is expected to continue until scrapie is eradicated from the United States. This means that with each passing year, the risk of your flock contracting scrapie is less, and one day, when scrapie is eradicated, genotyping will be irrelevant. When that day comes, will we long for some of the sheep culled in the past because they were QQ?

Every year since about 8,000 B.C., when it is believed sheep were domesticated, shepherds have worked tirelessly to improve the productivity of their flocks, many times at risk of life and limb. Under conditions that we can hardly imagine in modern times, they developed the art of selective breeding. We have inherited the fruits of these countless labors and now, as stewards of the flock, we also inherit the associated responsibility.

As we pursue a temporary genotype premium of a few hundred dollars per head, are we inadvertently throwing away something priceless? The science of genetic testing and selection is possibly the most powerful tool ever handed to humanity. Are we using our science as wisely as our ancestors used their art? (italics added)