Most of you with horses are familiar with various deworming products and today I am going to talk about a product containing moxidectin called Quest. This product was reviewed in Equine Veterinary Education by Drs. Schumacher and Taintor from Auburn University. Quest is in the same family of drugs as ivermectin but Quest is much more effective against the most serious parasite affecting horses at this time, the small strongyle. Small strongyles are unique in that horses ingest the larvae from the pasture and then become encysted in the horse's large intestine. This ability to encyst is important because encysted larvae are not killed by most of the regular dewormers used in horses, including those using ivermectin. This is one area where Quest has an advantage over some of the other products because it has been shown to kill encysted larvae. The only other product shown to kill encysted larvae is fenbendazole, which is sold under the trade name of Panacur. However, a regular dose of Panacur is ineffective and it takes a double dose of Panacur once daily for 5 days to kill these larvae. Also, Panacur is less effective against the other stages of the parasite than Quest.
A concern about Quest is the possible side effects of the drug as numerous drug reactions have been reported. However, most of the problems occurred due to accidental overdose of the drug or incorrect estimation of the horse's weight. So Quest may be a product you need to consider adding to your deworming program but you should use a weight tape to carefully estimate your horse's weight before using Quest.