Overview on Deworming Horses
  by Robert N. Oglesby DVM

Intestinal worms remain a serious and rapidly changing problem in horses and equines. While once we were concerned about the adult parasites drain on the horse's resources a careful examination of the life cycle reveals that the migrating larvae of the large strongyle was responsible for serious disease. This shifted the focus of parasite control to prevent the horses from being exposed to the infective larvae on the pasture. The advent of better anthelmintic (deworming) products had all but eliminated this problem where they were used. However recently increasing resistance to both the older and newer dewormers is causing another shift in deworming problems and populations and the problems with parasites continues: recurrent colic, diarrhea, poor doing, pneumonia, and death even in some regularly dewormed horse populations.

This article discusses important evolving concepts of parasite control that get away from the regular use of dewormers that has created the resistance problem. Also briefly discussed are the pros and cons of the various anthelmintics available and links provided to complete articles on these products:

• pyrantel pamoate (Strongid, Strongid C, others)
• ivermectin (Eqvalan, Zimectrin, others)
• moxidectin (Quest, others)
• fenbendazole (Panacur, Panacur Powerpack, Safe-Guard) and other benzimadazole dewormers (Anthelcide, etc...)
• praziquantel (usually in combination with an avermectin: Zimectrin gold, Quest Plus) dewormers.

Article Summary Intestinal worms remain a serious problem in horses and equines. Changing parasite populations and increased resistance mean many commonly used deworming recommmendations may not be effective and any program will have weaknesses. Whatever deworming program is used, proper management and frequent checking for efficacy will greatly increase the efficacy of your program.

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