Honors Program


Document Type


Date of this Version

Spring 4-2018


Rawlinson, Kate. Apr. 2018. Equine Anthelmintic Resistance.


Copyright Kate Rawlinson 2018


The rise of parasitic resistance to anthelmintic medication in horses is one of the most concerning topics to today’s horse owners, veterinarians, and those surrounding the industry. Much like the trend of resistance to antibiotics in human medicine, anthelmintic resistance poses a severe threat to overall horse population health as well as individual animal health. Many studies, both in the United States and countries across the world, have noted anthelmintic resistance in Parascaris equorum, cyathostomins, and other prominent equine parasites. These studies were conducted by determining the Fecal Egg Count (FEC, or the amount of parasite eggs shed) in the manure of horses before and after treatment with anthelmintic. Of the three major anthelmintic classes (benzimidazoles, tetrahydropyrimidines, and macrocyclic lactones), resistance to benzimidazoles is the most commonly observed for reasons that remain unknown. However, studies suggest that resistance to tetrahydropyrimidines and macrocyclic lactones is in the early stages of development. As there are no new active compounds coming onto the market in the near future, most researchers conclude that we must look for better ways to manage the anthelmintic medication distribution based on necessity and not necessarily on prevention. Furthermore, some studies have evaluated herbal parasiticide sources such as garlic, but these studies have been predominantly in vitro and have not been evaluated in live animals. Should natural therapies become a viable parasiticide, it appears to be the most readily available and logical anthelmintic. It is my conclusion that, in order to slow the progression of anthelmintic resistance in equine parasites, enforceable restrictions must be placed on existing deworming agents and research of natural therapies must be further explored.