Background
Previously, it was thought that by rotating wormers and worming often that we would eliminate all parasites in a horse population and reduce the risk of wormer resistance. We now know that to be false.
Lately, it has been discovered that there is a concern with wormer resistance because of excessive deworming and inappropriate deworming strategies. Current recommendations are to be more selective in our use of wormers and to target the life cycle of the worms.
The worms in question are becoming resistant to 2 classes of wormers called Benzimidazoles (Panacur and SafeGuard for example) and Pyrimidines (Strongid for example). So far the Macrocyclic Lactones like Eqvalen and Quest are effective. There is evidence that combining the first 2 types of wormers in a single dose is effective.
By disrupting the life cycle of the worms we can make our deworming programs more effective while worming less often. In our climate the worms we worry about are quiet over the winter. They become active in the spring. By worming at that time we potentially eliminate worm larvae from developing. By worming later we eliminate the worms we missed the first time. Finally, we worm after the first frost to kill bots.
Routine fecal examinations help us identify if our wormer program is effective and identifies those horses that are more susceptible to worm infestation.
Protocol
We are proposing 2 deworming strategies that are alternated each year to minimize the risk of dewormer resistance and offer the maximum protection to your horse.
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Year 1 (Choose 1)
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Year 2
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Ivermectin
April 1, June 1, August 1
Quest Plus
One month after the first frost
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April 1st- Ivermectin1 (Eqvalan)
June 1st -Fenbendazole (Panacur) + Pyrantel (Strongid)2
July 1st - Ivermectin1 (Eqvalan)
September 1st -Fenbendazole (Panacur) + Pyrantel(Strongid)2
One month after the first frost - Quest plus
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-- OR --
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Moxidectin4
April 1, July 1
Quest Plus
One month after the first frost
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1 8 weeks duration
2 4 weeks duration
3 effective against tape worms
4 12 weeks duration
Fecal Exams
Fecal exams are done prior to July or August worming then 2 weeks afterwards if worms are noted.
Special Circumstances
Broodmares: Worm within 1 week of foaling. This is to prevent the transmission of worms via the milk to the foals. Foals – Worm at 2 months of age with Ivermectin then every 2 months until 10 months old.
New horses: Worm and wait 3 days before allowing on pasture with other horses.
You can help reduce the worm burden on your farm by rotating pastures, picking manure from pastures and NOT spreading it.