Dewormer for Horses: What You Need To Know

Jennifer Rice, DVM, CVSMT
By Jennifer Rice, DVM, CVSMT on Apr. 25, 2022

Why Do Horses Need To Be Dewormed?

Deworming is one of the most important aspects of wellness care for horses. Parasitic worms live in the digestive tract (most commonly the small intestines) of horses and ponies. Horses are always exposed to worms by living outside. However, by implementing an effective deworming protocol, worms can be kept at a minimal level and can be well-tolerated within the horse. Parasitic worms become a medical issue when the number of worms increases to the point where they become burdensome to the horse's digestive tract.

Implementing an effective deworming protocol can prevent the following medical issues/emergencies: 

When Should You Deworm an Adult Horse?

Developing a deworming schedule for your adult horse should be based on their fecal egg count, lifestyle, and geographic location. The veterinarian will recommend a yearly fecal egg count in order to develop the best deworming schedule for each horse. Younger (below 5 years of age) and older horses (above 15 years of age) generally are at greater risk for having a larger worm burden due to their weaker or immature immune systems.

Fecal egg testing is a simple diagnostic procedure that looks at the amount of eggs in a fecal sample. Specifically, it is calculated in the amount of eggs per gram (EPG) of manure. Depending on the amount of eggs that are seen under the microscope, the horse will be classified as a low, moderate, or high shedder. Fecal egg counts should be performed at least once yearly, preferably before deworming in the spring. 

Classification of parasitic egg shedding

Eggs per Gram (EPG) of manure


0-200 EPG


200-500 EPG


Greater than 500 EPG


How to collect a fecal sample to be tested:

  • Collect a fecal sample in an airtight Ziploc® bag or container

  • Fresh samples (less than 12 hours old) are best

  • Refrigerate as soon as you collect the sample

  • Fecal samples should be tested within seven days of collection

It is important to note that diarrhea is not an acceptable fecal sample for testing for a fecal egg count. Frozen samples are also inaccurate, as freezing will damage the eggs and falsely decrease egg counts. 

Recommended deworming schedule based on fecal egg count:

Classification of parasitic egg shedding

Recommended amount of times to deworm per year

Time of year to deworm


Twice per year

Spring and fall


Three times per year or every 4 months

Spring, late summer and fall


Four times per year or every 3 months

Spring, summer, early fall, and late fall


What is the Most Effective Horse Dewormer?

All horse dewormers can be effective. Dewormers vary by their active ingredients, with each category of active ingredients treating a different type of worm. In recent years, resistance to utilizing only one type of deworming medication has been observed, therefore it is important to rotate what deworming medication you use to ensure efficacy. The best way to protect your horse from worms and choose the most effective dewormer is to discuss your unique horse's fecal egg count results with your primary veterinarian.  

Important points to consider when you are picking out a dewormer:

  • Season/time of year 

  • Parasite you are wanting to target with dewormer

  • What dewormer you used the last time you dewormed your horse

  • Geographic location 

  • Your horse's unique fecal egg count results

Generally, in the fall, it is recommended to deworm with a dewormer that has the ingredient praziquantel added to it (Zimectrin® GoldQuest® Plus, or Equimax®) in order to deworm against tapeworms.

Sample Adult Horse Deworming Schedule 

Low shedder (0-200 Eggs Per Gram of Manure)

Time of Year

Deworming Product Examples

Spring (March) 

Ivermectin (Zimectrin®, IverCare®), or moxidectin (Quest®) 

Fall (October)

Ivermectin w/praziquantel (Equimax®, Zimectrin® Gold) or moxidectin with praziquantel (Quest® Plus) 


Moderate Shedder (200-500 Eggs Per Gram of Manure)

Time of Year

Deworming Product Examples

Spring (March)

Ivermectin (Zimectrin®, IverCare®) or moxidectin (Quest®)

Late Summer (July)


Fall (October) 

Ivermectin w/praziqunatel (Equimax®, Zimectrin® Gold) or moxidectin with praziquantel (Quest Plus®) 


High Shedders (Greater than 500 Eggs Per Gram of Manure)

Time of Year

Deworming Product Examples

Spring (March)

Ivermectin (Zimectrin®, IverCare®) or moxidectin (Quest®)

Summer (June)


Early Fall (September)

Ivermectin w/praziquantel (Equimax®, Zimectrin® Gold)

Late Fall (November)

Moxidectin (Quest®)

How Do You Administer a Horse Dewormer?

  1. Look at the dewormer plunger, you will notice there are numbers indicating pounds. 

  2. Spin the stopper to your horse's estimated weight and remove the cap.

  3. Place the dewormer in your dominant hand, with your thumb on the plunger. 

  4. Stand on the left side of your horse's head and slip the open end of the dewormer in the corner of the mouth.

  5. Once the dewormer is in the horse's mouth, you can push the plunger until it hits the stopper.

  6. Once the dewormer has been given, you can remove the tube. Your horse will likely lick and chew at the paste or gel in his/her mouth. 

If your horse is adverse to the dewormer going in his/her mouth, you may need to take some time to desensitize them to the deworming tube. Practice putting a little molasses or honey on the end of the plunger and letting your horse get a taste of something sweet associated with the deworming tube.

Featured Image:

Jennifer Rice, DVM, CVSMT


Jennifer Rice, DVM, CVSMT


Dr. Jennifer Rice is a 2017 graduate from Purdue College of Veterinary Medicine where she specialized in Equine medicine. Since graduating...

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