OPPV News at the KHSI Expo

NursingI still have more notes to share from the KHSI Expo! Another speaker we heard from was Dr. Lynn Hermann-Hoesing, from the USDA-ARS-Animal Disease Research Unit at Washington State University. Her team is doing research on Ovine Progressive Pneumonia Virus, or OPPV. It is a costly disease that is likened to AIDS in humans- slowly progressive, it robs ewes of thriftiness, and eventually leads to premature death.

One in five sheep in the U.S. are infected, and one in three on the open range. There is correlation to flock size, larger flocks have a higher incidence of OPPV. It is estimated that OPPV costs the sheep industry about $2.7 million annually in lost productivity. The problem with OPPV is that it is often not overtly noticeable to the shepherd, but a flock will experience a smaller, less healthy lamb crop, and ewes that do not live a normal life span. So, the disease is of grave concern to the industry, and is often referred to as the “silent thief.”

OPPV is transmitted “horizontally”- from ewe to ewe; and is thought to be transmitted to ewe lambs not from their mothers directly, but rather after they are weaned and re-introduced to the flock. (This is new information from yet-unpublished research.) It’s a genetic affectation caused by a virus, and is irreversible; i.e. untreatable. Clinical signs only manifest in about 30% of affected ewes, and are not seen until the ewe is 4-6 years of age. When present, the signs are labored breathing, hard udder (mastitis), lameness and swollen joints (arthritis), productivity decrease with age, wasting, and occasional neurological problems.

Currently, the recommendation for controlling OPPV is to test annually (or twice yearly) for five years. Affected ewes can be retained and continue to be bred as long as they are productive and not showing serious clinical symptoms, with the plan of eventually culling them. But they must be kept isolated from the unaffected animals in the herd to prevent transmission. Tests run about $5/sample. So, given the cost and difficulty in maintaining two separate herds, many/most producers have not embraced this method of containment, to date.

Dr. Hermann-Hoesing’s team is working on a DNA test for OPPV, that would offer similar benefits as the scrapie DNA test. This would allow producers to test each animal only once in its lifetime, and progressively breed away from OPPV susceptibility, at a much lower cost than the current method. Their research is currently focusing on the Rambouillet, Columbia and Polypay breeds.The hope is to make progress there, and expand the research to include other breeds in the future.

This presentation sparked a lot of discussion and lively debate amongst the KHSI members in attendance. There is frustration felt amongst the few breeders who are following the recommended OPPV testing program, in that they are very limited in which other breeders from whom they can purchase ewes, because so few others are in the program. And, because they must pass some of this cost on in their sale animals, it makes it hard for them to compete with their non-testing peers. Some feel that KHSI should mandate OPPV testing amongst its membership, or those who register animals. But given the limitations of the current recommended program, this seemed to be very controversial and not widely agreed upon.

I currently have chosen not to test, for these very concerns. The $10/year per ewe doesn’t seem so bothersome, as I could consider it an investment in future flock productivity, and also in marketability of my animals. But, I don’t have the means to separate affected ewes, so I would have to cull them immediately upon finding out they were positive, which would be costly in another sense. For now, I’m crossing my fingers that a DNA test will arrive on the scene soon.

What are your thoughts on OPPV?

10 thoughts on “OPPV News at the KHSI Expo

  1. Jessica Howard says:

    From what I know OPPV and CAE (in goats) are both very similar diseases. I have yet to do the testing on the sheep, though I have considered it, but when they aren’t as tame as the goats and when we did the CAE testing for the goats I usually wasn’t interested in asking my friends to rustle the sheep, too!
    I do test yearly for CAE with my goats, and so far I have always been negative, and plan to keep it that way! We have the SAME problem in the goat world with MANY people not testing for CAE! We send our samples in ourselves to WSU and the last cost was $10 plus $4/head and shipping.

  2. Michelle says:

    Jessica, yes, I think you are right, Dr. Hermann-Hoesing did mention CAE is the goat equivalent of the disease. It seems like it would be even more important for dairy goats, where milk production is paramount, and you’d notice a decline once does started suffering from the symptoms of a diease. I suppose your case would be the idea one- if you start the testing, and find you don’t have it, then viola, you are done and can declare yourself clean in five years!

  3. Doris says:

    Yes, that’s what I thought, it sounds so very similar to CAE in goats. In Pat Coleby’s book, Natural Goat Care, she says once she got her animals properly mineralized, she no longer had problems with CAE and CL and a plethora of other issues that afflict mineral deficient goats. While I have yet to get her book on sheep care, I imagine she has much the same thing to say about sheep as she says the same things re: cows and horses. So my goal is to get my sheep mineralized the same as the goats. I know the sheep I’ve had in the past that I’ve fed the same as I feed the goats were very tender and tasty. I even had an Australian tell me that was the best sheep he has ever eaten. So that is my two cents, =)

    Thank you for sharing. I feel that I have learned a lot from your seminar.

  4. bruce king says:

    There are treatments for animals that don’t make economic sense. Just taking what you’ve said in this post, here’s a look at it:

    paraphrased: “One in five sheep is infected, and that sheep will not live as long or have as healthy a lamb. ”

    If you have a flock of 100 sheep, you’ll be spending $1,000 a year to test them. At current market rates, that’s equivalent to buying 8 to 10 lambs. (everson auction market auction results,


    So every year you could add 8 to 10 ewe lambs to your flock for the same as you’d spend on testing, and those 8-10 would add 8-20 lambs to your flock next year.

    I don’t think that testing makes economic sense. If it did, the big producers would be testing and segregating.

  5. Michelle says:

    Bruce, I think it’s more complicated than that. I think the 1 in 5 statistic is nationwide (and that’s small hobby flocks only, commercial flocks are 1 in 3), but is not evenly distrubuted. So I think flocks that are infected have a much higher incidence *within* the flock. You have to remember some flocks are not infected at all, so the 1 in 3 or 1 in 5 overall statistic implies higher concentration inside affected flocks.

    For affected flocks, that could be half their animals. If the affected animals are barely managing to produce singles each year, it’s questionable whether they are even replacing themselves. You waste years figuring out which ewes are unproductive and need to be replaced, while they could have been cranking out healthy twins. And when you bring in new ewe lambs, you expose them, so maybe at least half of those will become infected, and have their reproductive lives also limited.

    In commercial flocks, ewe lambs usually don’t twin their first year, so they are not as valuable as replacement animals as a good-producing mature ewe, there is a 2-year investment before you get them to their most productive years. So I think the concerns are valid- an infected flock is constantly operating at far less than full capacity, even for commercial operations.

    It’s hard to know if it’s equivalent or greater to the cost of doing a test/cull program for five years, then closing your flock to stay clean. But I bet the math probabaly works out.

  6. bruce king says:

    Lets take a small flock of 20 animals. Lets say that they’re all infected and produce only one lamb each.

    For the first year, since one lamb is what you’d expect, there’s no benefit for testing. You now have 40 sheep (20 to start, 10 females, 10 males), but you’re out $200 for testing.

    With No testing, you have 43 (20 ewes, 10 male and 13 female) sheep for the same money.

    So in the first year, with all animals infected, you take a loss if you test.

    Year 2:
    For non-infected sheep, you start with 30 ewes, and get 30 male and 30 female, assuming everyone twins. You’re also out $250 for testing. You end up with 90 sheep.

    for the infected sheep, you start out with 33 sheep, and get 15 male and 18 female lambs, using the testing money to buy more ewe lambs. You end up with 66 sheep.

    So in year 2, you get roughly 25% more lambs. But this is assuming worst-case. From your examples, your flock might contain some sheep that are infected, and some that are not.

    Lets do the math with only half of your sheep infected in year 2:
    Start with 33 sheep, you get 1 lamb from 16, and 2 lambs from 17, and you buy 4 ewes with the money that would be otherwise spent testing. You end up with 87 sheep.

    So if less than half of your flock is infected, you’re still losing money testing in year 2. I don’t know about the lifespan thing — but from this thumbnail sketch, it doesn’t look like testing is a clear winner in any way.

  7. Michelle says:

    Hey Bruce, good thoughts. I imagine the decision probably unique to each producer, how many sheep they have, their value, the breed, and what is considered “ideal” as far as what they could produce given perfect circumstances versus OPPV scearios.

    I ran some numbers for what I would consider “my” case (and now I’m starting to talk myself into wanting to start testing…). I’ll start with the assumption that registered ewelamb Katahdins go for $200, and I can also sell lambs for that for the meat market, and can sell breeding lambs for more when the ewe has an excellent production history.

    So, a perfect case: a healthy ewelamb I purchase for $200, she cranks out 5 twin set and 3 triplet sets, and lives long enough for me to sell her as dog food mutton at $75 at age 8. She could net me $4375 in her lifetime.

    On the contrary, if she is unhealthy, manages to have twins her first year, but then singles her 2nd year, I give her a break, keep her around 1 more year, and she singles again. By now, her value is low, I can’t re-sell her as a breeder animal, so she’s mutton for the meat market. Maybe I get $75 for her, at best. I buy a replacement ewelamb for $200. Say this one now gets infected and repeats the cycle, by her 3rd year, she’s only produced 4 lambs, so I sell her as mutton grind too, and replace her again. The third ewelamb does the same thing, so by the end of year 9, I’ve only netted $2025 on this string of ewes.

    So, it would appear that just in the #lambs produced, it could be more than a factor of two in net profit over 8-9 years. I haven’t considered feed, and I think that worsens the effect: if the affected ewes and their lambs are not as thrifty, they will require more investment in feed to bring the lambs to market weight. And possibly more costs in veterinary-type care, in trying to help along sickly animals by some means or another.

    So, say you have 20 ewes and a third of them are affected. This means that instead of the flock making $87.5K over 8-9 years, they are making about $16.5k less. If it’s possible that that the test/cull program, even if it costs several grand over 5 years to test ewes and replacement ewes, leads you more quickly to a clean, high-producing flock; maybe it’s a good ROI for the longer term?

    I’ve also read about some people who test their whole flock the first year, then only a select percentage of the flock after that (presumably animals with questionable performance, so you are intelligently choosing where the test dollars go). This might be the wisest option, to keep the cost manageable, but still increase your odds of thinning out the affected sheep earlier than you might notice them otherwise.

  8. bruce king says:

    you have a better feel for the market than I do. I purchased my triplet breeding stock this year for $225/ewe. So when I was looking at what the market is, the auction price seemed to be a fair way to go.

    Breeding animals usually sell for a premium over meat animals, so if your primary business is producing registered breed stock, it might make sense.

    What I don’t get is if your herd tests clean and it’s a closed herd, where does the disease come from?

  9. Jessica Howard says:

    In the case of CAE (the goat version of OPPV) if the goat comes from a herd that has CAE, or you bring any animals in that have been exposed to CAE (other herds, shows, running w/bucks for breeding, etc…) you can have goats convert from negative to positive! Even after several years of being negative. I know one friend who had CAE+ does years ago would never trust the test results on first generation animals, even when she pulled the kids right away, raised separately from the CAE+ goats, and were raised on pasteurized milk.
    I know in the goat world if they have positive animals they raise them completely separate (a minimum of 6′ alley ways between fences or pens), they also pull all the kids and raise them on pasteurized colostrum and milk. But even then you still have the risk of conversion, as CAE is passed via body fluids containing white blood cells (blood, milk, etc…), or if your milk wasn’t pasteurized correctly.
    So, the big problem I can see with sheep, if you don’t test, is that those lambs are nursing on their dams (if you have positive dams), so you are continuing to spread the disease to the next generation. As the whole point with sheep is for THEM to raise their lambs, not the shepherds pulling them and raising them separately to stop the cycle.

  10. Michelle says:

    Here is an explanation of the tests:
    The two more affordable tests, AGID and ELISA, look for antibody response, which may not be present in measurable quantities the first couple years the animal is infected. So thus the recommended 5 years of twice yearly testing, to try to “catch” those who start to show antibody response as soon as possible and get them out of the group. So, not a perfect system for sure; I would imagine if you have OPPV in your flock, you’re going to miss some for a while, giving them a chance to spread it, so it could take a few years to do a convincing job of getting rid of it.

    There is a third test that identifies the presence of the virus itself, but it’s too expensive to be practical.

    Once your flock is “truly” clean and you close it, then as long as the only new animals coming in are males, I think you continue to stay clean, as with scrapie.

    Bruce, I agree, I don’t know what the math looks like for commercial producers, if they are making more like $100 a lamb. Then I suppose the gap narrows, they can almost buy a replacement ewe for the price of selling the cull ewe for dog food. But, then again, even if they only lose $5 or $10 on each replacement ewe transaction, added up over a very large herd, it still may make some kind of OPPV testing strategy pay off; maybe at least selective testing.

    But it sounds like most commercial producers are making such paper-thin margins on wool sheep these days, that maybe nothing can save their industry (in this country at least)…

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