Ewes1I have written before about being concerned about Ovine Progressive Pneumonia Virus, or OPPV. It’s a non-curable virus passed between sheep which manifests in immune system problems; notably painful joints, poor milk supply, ill thrift, and weak lambs. At first, I was reluctant to spend the money on blood testing for OPPV,  it’s fairly costly. Then, since a buyer was paying a vet to come out and test his purchased ewes, I went ahead and tested the rest of the flock. Seeing that they were all clear, I figured this was a marketing opportunity, since some buyers value OPPV-free breeding stock. Since then, I’ve become proficient at collecting blood samples myself, making the testing less expensive than if I had to pay a vet to do it. Also, the more I read about OPPV, the more I became convinced I don’t want it in my flock. But still, the subject has been kind of an abstraction for me.

Until an acquaintance of mine got it in her flock.

She told me she didn’t realize what was going on right away. OPPV seems to be one of those frog-boiled-slowly kinds of things, where you don’t really realize you have a problem until it’s a bad problem. Until finding ewes dead in the pasture is a regular occurrence, and a lot of unthrifty ewes are getting sent to the butcher. You also have tons of bottle lambs: either because they are too weak to nurse, or because their dams lack enough milk to feed them. And, losses, losses, losses.

My friend described losing a lot of time trying to diagnose what was going on. She and a vet chased some red herrings, like thinking maybe a bacterial infection was sweeping through, brought in by flood waters. When she was finally led to test for OPPV, a large percentage of her flock was found to be affected and had to be culled. She said when she went back through her records, the path of the disease was suddenly so clear: all the bottle lambs from multiple years back had OPPV-positive dams. And the multiple years of losses and poor performance all lined up neatly with who had the disease and who didn’t. It explained everything.

Lambs1Her experience crystallized for me what writings from strangers in other parts of the country didn’t: this is real, it’s serious, and it’s very costly. And, it’s here, in our area. She has sheep sourced from many of our local friends and breeders as well as from out-of-state. She’s also sold sheep to a lot of people around here. So it’s impossible to know where it came from, and where it’s gone. This really made me digest the reality: there aren’t that many Katahdin breeders in our area; and we all trade sheep back and forth. It’s likely a lot of flocks have it, out of all the untested flocks in the area. And, that’s most flocks. Maybe some people comfort themselves into thinking “but I haven’t had any of these symptoms or losses.” But this could be naïve, because a loss here and there isn’t going to clue you in: it’s not until you’ve let it spread insidiously for several years before you’re going to start seeing these big trends of performance issues. By then it becomes a very expensive phenomenon from which to recover.

I should say here, there are people in the world who think OPPV isn’t a big deal. Dr. Kennedy at Pipestone being one. But many other renowned veterinarians and researchers are very concerned about OPPV, and a lot of research is being done on it. It’s the new scrapie, if you will: the next big thing that’s believed to create severe economic losses across the industry. Given this, and my friend’s account, I think I’ll err on the side of conservative and keep it out of my farm. I think of it as an insurance policy.

As luck would have it, I had a ram from this friend, and he ended up testing positive. I found out last fall, just before breeding season, soon after she told me about her situation. I hand-wrung over what to do. I had multiple ewes that couldn’t be bred to my other rams due to inbreeding. I needed this guy. I had to make the choice to rush out and find another ram, gamble on some inbreeding, or go ahead and use the affected ram. Plus, he had important genetics from another part of the country that I wanted to leverage. At the time, writings I could find about OPPV indicated that the most common transmission vector was “vertical”: from mother to lamb. Supposedly, “horizontal” transmission between adults was less common and unlikely. So, I went ahead and used the ram on a small group of ewes, choosing carefully that none of my best ones were paired with him, to reduce their exposure.

For people who test for OPPV, the recommendation is to test ewes just prior to lambing, so that if you catch any positive ones, you can orphan-rear their lambs to prevent their exposure to the disease. I am loathe to manhandle my ewes when they are pregnant, though, so I ended up testing right after lambing. Lo and behold, one other ram and two ewes tested positive. In the meantime, some new research papers have been published that indicate OPPV spreads horizontally more than was originally thought. So it would seem to be true here!

The ELISA test for OPPV is not 100% accurate. It’s specificity is 98.4%, meaning there is a 1.6% chance of getting a false positive. The sensitivity is 95%, meaning there is a 5% chance of getting a false negative. So, the recommendation is that we test twice yearly to catch the false negatives, and re-test any positive animals before culling them.

I did perform a re-test on the positives, and good thing, because the nicer of the two ewes that tested positive came back negative the second time. I culled the other three, which was extremely disappointing, as they were all very nice breeding animals in prime condition. But, I felt I just couldn’t take the chance of having it spread any further. Fortunately, OPPV doesn’t affect the meat in any way, so these animals are all now in our freezer.

The bigger dilemma was what to do with the lambs born to the two ewes. I was regretting not testing my ewes before lambing commenced so I could have orphan-reared those lambs. In the second round of testing, I submitted samples of the lambs; and I also sent their blood samples off to Geneseek to use the new test which looks for genetic resistance to OPPV. I wasn’t really sure what I would find, but I just wanted to know.

The ewe that tested negative in the second round seems to be in the clear for now, and all three of her lambs also tested negative. Coincidentally, she was the ewe that earlier had a pile of simultaneous health problems and nearly died; so when her first test came back positive, I thought, well that explains everything.  Except, now it doesn’t. This part is puzzling, perhaps random chance, perhaps there is some correlation we cannot yet explain.

The for-sure positive ewe had twins, but one was hmm– a bottle lamb, which died early of- hmm, strange weakness and inexplicable ill health, despite treatment. Just the very thing OPPV causes! The remaining healthy lamb’s blood test came back negative for OPPV. That is really interesting, because according to this graph from Dr. Leymaster’s slides on OPPV:

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even if she didn’t have OPPV, she still should have tested positive at the age of three months when I tested her, due to maternal antibodies coming from the milk she drank. But, it turns out she also has the resistance gene combination, so perhaps that explains her negative blood test. Lucky. I will keep her in the flock and keep her on the re-test schedule and see what happens.

So, for now, I think my flock has the all-clear again, and I will re-test in the fall to catch any lurking cases. I hesitated to write about it, because there is that strange psychological affect where people may steer clear of someone who discloses incidence of a disease, opting to buy animals instead from someone who doesn’t test at all. We all know the saying “better the devil you know, than the devil you don’t.” But not everyone adheres to that logic. So I hope this doesn’t impact sales of breeding sheep. If it does, oh well, there is always room in the butcher market. Anyway, I feel that I have done the right thing by being transparent about it. I think it’s important that people discuss these things openly so we can learn from each other, and nobody learns anything if everybody stays secretive.

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