for horses. It can be used for a wide range of targets including species of the Strongylus nematode. It also is effective against bots. However, having been used heavily for decades, there are concerns that some nematodes are developing resistance. Deworming There are two common methods of deworming. Purge dewormers that kill parasites with a single strong dose, are given periodically, depending on local conditions and veterinary recommendations. Continuous dewormers, also known as "daily" dewormers, are given in the horse's feed each day, in small doses, and kill worms as they infect the horse. Neither of these methods is perfect; purge dewormers are effective for rapidly killing parasites, but are gone from the horses' body in a few days, and then the horse may start to be re-infected. Continuous dewormers are a mild low dose and may be easier on the horse, but may not be effective in quickly killing worms in a heavily-infected horse and may contribute to drug resistance. If a treatment doesn't kill at least 95% of a worm species, that species is classed as 'resistant' to the drug. For adult horses, frequent rotation of several types of dewormers is no longer recommended, as it can often lead to overtreatment and subsequent drug resistance. Another way of combating drug resistance in adult horses is to deworm less frequently, by performing fecal egg counts on manure and deworming only horses with a high count. This strategy is now recommended by most veterinarians and parasitologists, as it reduces the probability of resistance. For horses that are consistently deemed "low shedders," it is still recommended to deworm at least 1-2 times per year with ivermectin + praziquantel or moxidectin + praziquantel to target tapeworms, bots, and small strongyles. This is typically done in the fall and spring. Dewormers come in several forms, including pastes, gels, powders, and granules or pellets. Powders and granules normally come in single-dose packaging, and the dewormer is normally mixed in with the horse's feed. Pastes and gels normally come in a plastic syringe which is inserted in the side of the horse's mouth and used to administer the dewormer onto the back of the horse's tongue. A dewormer syringe has a plastic ring on the plunger that is turned to adjust the dosage for the horse's weight. Precautions in deworming Drug resistance is a growing concern for antiparasitic medications. Resistance has been noted with ivermectin