Horse owners have been following the same deworming protocol for decades – administer a dewormer every other month, and rotate the type of dewormer you use.  Recent studies have found that these practices are outdated and unnecessary.  So what should you do to protect your horse from parasites?  Recommendations vary based on your horse’s risk.


Why change parasite control methods?

Due to increasing patterns of parasite resistance and new knowledge of individual horse’s egg shedding levels, traditional deworming protocols are being re-examined.  Widespread resistance of small strongyles and roundworms has been documented to many classes of dewormers.  Adult horses vary in their innate ability to resist infection and shedding of parasite eggs and thus require individualized approaches to deworming to slow resistance patterns. It has been documented that 20% of horses shed 80% of infective eggs. By only treating the individuals with moderate to high Fecal Egg Counts (FEC), you can eliminate 95% of overall egg shedding.


What are the new recommendations?

All adult horses should receive 2 foundation treatments per year. Low shedding individuals will need no other treatments as they are naturally protected by their immune state.  Repeated treatment of these horses does little for their health, but can contribute to drug resistance.  Moderate and high shedders will need 1-2 additional treatments per year. The goal of modern parasite control is to control egg shedding and limit infection so that your horse remains healthy, as well as avoid further resistance so that efficacious dewormers remain available. Horses less than 3 years of age require additional attention as their immunity to infection has not developed yet.


How do I know if my horse needs additional treatment?

strongyleIt is recommended that all horses have an annual fecal exam performed to determine their Fecal Egg Count (FEC). A fecal sample is collected several weeks after the last dewormer was administered, depending on the type that was used. A fecal sample should be fresh (<12 hours old) and refrigerated in an airtight container or plastic bag.  Bring the sample to EVA within 7 days for testing. The sample is evaluated to determine the number of Fecal Eggs Per Gram (FEPG).  The horse is then classified as a low, moderate, or high contaminator based on his/her FEPG.  This classification is used to create an individualized parasite control program for your horse.

Another useful test is a Fecal Egg Count Reduction Test (FERCT). A fecal sample is collected and tested prior to deworming. A second sample is tested 14 days after deworming and compared to the first sample.  This test is performed on multiple horses in one location to determine if parasite resistance to a certain dewormer is present.


Available classes of dewormer and their uses:

  • Benzimidazoles: Fenbendazole (Panacur, Safeguard) and Oxibendazole (Anthelcide). Effective for large strongyles, early indications of resistance for roundworms, widespread resistance for small strongyles.
  • Tetrahydropyrimidines: Pyrantel (Strongid). Effective for large strongyles, resistance common for small strongyles and roundworms.
  • Macrocyclic Lactones: Ivermectin (Eqvalan, Zimectrin) and Moxidectin (Quest). Effective for large strongyles, bots, and some small strongyles.  Widespread resistance in roundworms.
  • Isoquinoline-pyrozines: Praziquantel (in combination with Moxidectin as Quest-Plus and Ivermectin as Equimax). Effective for tapeworms.


Deworming Tips:

  • Do not under-dose your horse- use weight tapes to determine accurate body weights.  You can pick one up for free at our clinic!
  • Use FEPG to determine shedding status of new horses before turning into common pastures.
  • Talk to your veterinarian as different management practices and stocking densities can affect deworming recommendations.


Deworming protocols for mature horses:

  • Focus on control of small strongyles by using FEPG to identify high shedders within your herd, and deworm them appropriately.
  • Include yearly treatment for bots and tapeworms, ideally in late fall/early winter.
  • Include 1-2 yearly treatments for large strongyles.


Sample schedule for adult horses
Spring (March) FEPG to determine shedding status, administer dewormer of choice for large strongyles
Summer (July) FEPG recheck on any previously high shedders, deworm these individuals according to veterinarian recommendations
Fall (November) FEPG recheck on any previously high shedders, administer Praziquantel product for tapes combined with boticide


Deworming protocols for young horses:

First year of life: focus on control of large strongyles and roundworms. Additionally, recently weaned foals should be turned out on cleanest pasture available to decrease exposure to parasite eggs.


Sample schedule for first year of life
2-3 months of age Benzimidazole product
6 months of age Benzimidazole product
9 months of age Macrocyclic Lactone product
12 months of age Macrocyclic Lactone + Praziquantel product


Yearlings and 2 year olds should be treated as high shedders, receiving 3-4 yearly treatments with appropriate medications. Consult with your veterinarian for deworming recommendations.


Download our Parasite Control Guidelines for a quick guide to deworming.