Test Your Knowledge of Management Practices That Affect Dewormer Resistance

Thanks to Michelle Arnold for this excellent article! There are many important diseases in sheep and goats but none are as common or threaten the herd health as much as internal parasites (worms). Although there are many types of worms that may contribute to a parasite problem, the blood-sucking barber pole worm (Haemonchus contortus) is the most prevalent and most important, especially in the southern US. This parasite causes the highest death loss in young animals during their first year on pasture, especially around weaning time. Traditionally, parasites have been controlled by frequent, regular administration of chemical dewormers. However, with the emergence of multiple drug resistant parasites, new approaches are required. Resistance is a genetic change in a population of worms that allows some individual worms to survive and multiply despite administering the proper dose of dewormer at the right time. It is now essential to view all dewormers as extremely valuable and limited resources that must be used intelligently with prevention of resistance as a goal. It is a well-known fact that 20% of animals harbor 80% of the worms in a typical herd. After these 20% are identified for treatment (usually by FAMACHA©), then a dewormer must be selected and administered

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