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Safe wormers for ewes with new lambs


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I manage a flock of sheep with fairly heavy (relatively) parasite loads. It's nothing like the south east US, and the flock has been pretty heavily selected for resistance. I'm working pretty hard on reducing the parasite load on these pastures- removing the sheep is not an option, unfortunately.


This year, I'm thinking about dosing the ewes with wormer right after they lamb. I bring them into jugs after they lamb out on pasture, then they'll move to a clean pasture after being in the shed for 24-48 hours. My sheep books say to use ivermectin, but it's useless on this flock. Is Cydectin safe to use? Other wormers?


Also, is it worth it to do this?



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Our Iowa Sheep Industry Newsletter just came, in it is a reprinted article from Piperstone Vet Clinic Sheep Newsletter Feb 2005. The advice is to worm ewes as they go through the lambing jugs or in the week following lambing, if I'm understanding the article correctly they are saying to worm the ewe at the same time you are doing other processing procedures with the lambs. They give no suggestions as to what wormer to use.


They talk about the worms burrowing into the intestinal tract lining and going dormant until the hormone shift causes them to migrate. I have seen first hand while butchering adult animals the worms imbedded, in one it was in the tissues that lines the stomach cavity just inside the ribs. I have also had animals showed no purge of worms until after they gave birth, and then a huge load was purged with wormer was administered.



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Hi Ben,


The only caution about any of the dewormers labeled for sheep is on Valbazen, which should not be used in early gestation as it can cause fatal birth defects in the lambs. You can certainly use Cydectin, but you might want to consider alternatives as it is in the same family as ivermectin. It tends to retain efficacy for a while in flocks that have demonstrable ivermectin resistance, but not forever. The longer you can delay using it the better. It is the only ace up your sleeve for the foreseeable future. *


I believe that levamasole (Probibit) is back on the market at least in a limited way. I would consider using that if you can get enough of it. Valbazen would be the other choice.


The practice of deworming ewes at lambing time as they are processed through the jugs is a time-honored one, and for good reason. As ewes approach lambing two things happen that increase parasite activity. First the hormones associated with birth and lactation awaken dormant larvae, which mature and being producing eggs. This is a brilliant evolutionary adaptation on the part of the parasites, since those hormones indicate that there's a large new crop of hosts on the way for them.


Second, the stress associated with lambing tends to reduce the ewe's immune response, allowing those newly awakened parasites to thrive more than they might at another time of the year.


In an ideal world, you'd probably want to deworm the ewes again about two weeks after they lambed, but that would usually mean mismothering and trampling of baby lambs.


*There is a new class of wormers that has been approved in NZ. When or if it will be approved in the US is anyone's guess.

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After lambing, the teratogenic effects of the chemical are no longer of concern. It's only while the fetus is developing in the early stages of pregnancy that Valbazen can cause serious anamolies. I usually use Valbazen to take care of tapes once a year in the summer when no one is pregnant.



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Thanks, everyone.


Bill, since we also have dairy goats (just pretend that says 'sheep' or 'cows'), I'm used to looking for a milk withdrawal warning, which some wormers don't have. I suppose it probably isn't so much of a deal since these sheep aren't producing milk for human consumption. I have, unfortunately, already had to use Cydectin on this flock. I've used it twice, I think, and I'm trying not to use it.


I've had the best luck reducing parasite loads by grazing my horses behind the sheep, and by running poultry through my sheep pastures. The poultry have the added benefit of fertilizing, too.

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