Parasites – one more look before winter

All summer and fall, I have been writing about the fact that this year has been a rough one for our sheep when it comes to parasites. I’ve repeated this so often that I won’t go into all of the background here, but did want to give an update for those wondering what I have uncovered in my work on this issue. I had mentioned in my last posting on the subject that our bloodlines were doing quite well in the field with exceptionally high fecal egg counts (FECs), a result of our selection strategy for these past many years. Yet, when they did end up with anemia as a result of those many internal parasites, I was finding that even a dewormer that was 95% effective against them was still not bringing the FEC levels down to where the sheep could recover well and thrive – there were just so many eggs that even 5% of what was originally there was still considered to be too high for a good recovery.

So, I’ve been approaching this problem on two fronts: trying to reduce those high FECs for this winter so that all of our sheep can recover some strength while avoiding re-infestation due to the cold Iowa winter, and also trying to figure out a way to reduce the number of dormant eggs in our fields to avoid high levels of re-infestation next spring when the weather warms (and also avoid heavy worm loads in next year’s lambs). As I began this investigation, I will admit that I felt out of my depth – this is such a complicated issue.

Yet, I have chipped away at these two aspects for some time now and am beginning to develop a strategy. My immediate concern was the first: reducing the current FECs of our sheep to recovery levels, and in that, I have made good progress. We have been using Cydectin as a dewormer for our sheep, and because it was not bringing those FEC levels down to¬† recovery levels even with a high kill rate (somewhere over 93%), I needed to look at additional measures. I came across another dewormer with the active ingredient levamisole that – from what I could tell talking to vets and experienced sheep producers – was considered no longer very effective because it was one of the first dewormers in use. Because it hadn’t been available for a very long time (since about 14 years ago or so), my thinking was that our parasites had not been exposed to it recently and might have lost any resistance they may have once had. I treated my three “test” ram lambs, Poet, Perrier, and Putty, with this dewormer a couple of weeks ago and waited for FEC results.

As it turns out, I was right on! The Cydectin dramatically reduced their FECs from the tens of thousands of eggs per gram to only hundreds, and then the levamisole brought those levels down to near zero in two of the lambs, and only fifty eggs in Perrier. Why didn’t Perrier clean up as well? There is no way to know – but the point is that even at 50 eggs per gram, this is well into a recovery situation for this lamb (particularly compared to a beginning count near 30,000 eggs per gram!). It seems that if I want to clean up our flock after this very heavy parasite year, I will need to use a sequence of dewormers over a period of a couple of weeks once the weather is too cold for reinfection during grazing.

As for the eggs already out on our pastures, I have a couple of options. Since the parasites on the fields are essentially eliminated if they are left without livestock over the period from Jan 1 to July 1, or from July 1 to Jan 1, I can allow our sheep to graze only half of the acreage in the early part of the grazing season next spring, allowing the parasites on the other half to die off – then deworm the flock and switch them to the other half of the acreage for the second part of the grazing season. Another way to do this is to make hay off of portions of our acreage – once hay is harvested from a piece of land, the parasites once there have been eliminated. Cycling through our acreage baling hay then also result in essentially parasite-free grazing. Finally, another option is to trade grazing space with people who have other species: if horses or cattle graze our land while our sheep graze their acreage for the first half of the growing season (until July 1), both farms will eliminate their species-specific parasites.

Although there are various options here, finding the right option will be tricky. It is important to me that our lambs graze alongside their mothers for a good part of their pre-weaning lives – otherwise, they go into adulthood at a disadvantage, never having learned from their dams which vegetation is edible. This leaves them at risk for accidental poisoning – a situation that we definitely don’t want. When our lambs go to other farms, we want to make sure they are ready and able to thrive and produce coming generations without issue.

Sending our sheep to graze at other nearby farms also involves some issues that are likely not obvious at first. Since I provide a lot of supervision to our young lambs, having them here just outside our back door makes it easy to keep on eye on them, allowing me to catch illness or injury quickly and giving them the best chance at survival. Trading grazing land for a period will mean that checking on the flock will likely require me to drive over to wherever they might be, limiting how often I can check on them each day. Besides that, the fencing for cattle and horses is different than for fiber sheep (think barbed wire rather than smooth) and can wreak havoc with sheep coats. This is an option that seems great at first, but becomes quite complicated as the reality and details set in.

I’m not yet sure how I will handle the parasites in the fields, but thankfully, I have all winter to figure it out. I know how to treat the flock itself, and I’m sure the rest will come to me eventually!

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1 Comment

  • Jane says:

    Well I think this topic is fascinating or at least that you have made it so. The critical thinking required to stay ahead of such a problem is quite exciting to watch.

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