Until now, it has been common practice to routinely worm horses with tapeworm wormer, regardless of whether the horse has a tapeworm burden or not. In a routine worming approach, horses are wormed once or twice a year, traditionally during the spring and autumn. Worming programmes such as these inevitably lead to worms building up resistance to wormers. A build-up of widespread resistance would have devastating consequences, especially as there are only two drugs available for the control of tapeworm in horses. These drugs are praziquantel and pyrantel embonate (double dosed). See the table below for information on which wormers control tapeworm.
Resistance to wormers
Using routine worming approaches, horse wormers (anthelmintics) are often over-used in the equestrian community. It is thought that the majority of worms are present in just a small percentage of the horse and pony population, and the unnecessary, widespread dosage of wormers in horses is now causing drug resistance.
With increasing reports of anthelmintic resistance in small redworms (cyathostomes), special attention should be paid to the management of tapeworm in horses, to ensure resistance does not build in tapeworm as well. Frequent use of wormers puts tremendous selection pressure on the worms to adapt to survive this continuous onslaught and the result is a relentless, steady emergence of resistance. Additionally, under-dosing your horse also encourages resistance, as an insufficient dose which does not kill all of the worms, exposes surviving worms to the drug, giving them the opportunity to adapt and develop resistance.
Targeted worming approach for tapeworm
Regular EquiSal Tapeworm testing now provides the means to adopt a targeted worming approach for tapeworm. It is recommended that horses diagnosed as borderline or moderate/high are wormed for tapeworm whilst those with a low diagnosis do not need worming. Many horse-owners are already using a targeted worming approach for redworms and roundworms, basing the use of wormers on faecal egg counts which determine whether a horse has a worm burden that demands treatment.
The key message is to carry out routine testing and not routine worming, reserving the use of wormers for when they are recommended following diagnosis of a worm burden. It should be noted however that no diagnostic test is available for encysted redworm so all horses should be given a winter worming dose with a product containing moxidectin.