Deworming a horse correctly means using the right drug at the right time, often guided by testing, instead of just guessing. This approach helps control harmful parasites while slowing down the growth of drug-resistant worms.
Why Proper Deworming Matters for Horse Health
Keeping parasites in check is vital for your horse’s well-being. Worms cause many problems. They steal nutrients, which can make your horse thin or weak. Some worms cause serious damage to organs or the gut. Good equine parasite control stops these issues before they start.
Recognizing the Signs of Worms in Horses
How do you know if your horse needs treatment? Look for common signs of worms in horses. These signs might not always appear, especially if the worm burden is low.
- Poor coat condition (dull, rough hair)
- Weight loss, even if eating well
- Diarrhea or colic episodes
- A pot-bellied appearance (common in foals)
- Lethargy or low energy levels
If you see these signs, talk to your veterinarian right away. Early treatment is always best.
Moving Beyond Old Deworming Habits
For many years, horse owners followed a set schedule. They would deworm every six to eight weeks, no matter what. This method, called routine deworming, has caused big problems. Many parasite species have become tough against common treatments. This is called equine dewormer resistance.
Modern horse care focuses on targeted treatment. This means only treating the horses that need it, and using the correct medicine for the worms present.
The Role of Fecal Egg Count Testing
The key to modern worm control is the fecal egg count (FEC). This simple test tells you how many strongyle worm eggs your horse is passing in its manure.
What the FEC Tells You
The FEC result helps categorize your horse into a group:
- Low Shedders: Pass very few eggs. These horses need less frequent treatment.
- Moderate Shedders: Pass some eggs. They need regular checks.
- High Shedders: Pass many eggs. These horses need treatment most often to protect the whole herd.
A high FEC score means your horse is shedding lots of parasites onto the pasture. This increases the risk for all horses sharing that space.
How to Get an FEC Done
- Collect a Sample: Collect a fresh manure sample directly from the pasture or the horse’s droppings (not dirt mixed in). You need about 2-3 fresh manure balls. They should be less than 12 hours old.
- Store It: Keep the sample cool, but do not freeze it. Bring it to your vet or lab as soon as possible.
- Wait for Results: The lab counts the eggs per gram (EPG) of manure.
Always discuss your FEC results with your veterinarian. They can help you decide which drug to use based on regional resistance patterns.
Selecting the Right Anthelmintic Drugs for Horses
There are several types of anthelmintic drugs for horses. These medicines kill the worms inside the horse. It is important to use a drug that targets the specific worms you are trying to control.
Major Drug Classes Used
We use different drugs for different worms. Modern treatment plans often rotate between these classes or use a drug that hits many types of worms at once.
| Drug Class | Common Active Ingredient Examples | Primary Targets | Notes |
|---|---|---|---|
| Macrocyclic Lactones | Ivermectin, Moxidectin | Small Strongyles, Large Strongyles, Pinworms, Lungworm | Very effective against most common worms. Moxidectin often lasts longer. |
| Benzimidazoles | Fenbendazole, Albendazole | Small Strongyles, Tapeworms (some types), Roundworms | Fenbendazole is popular; use higher doses for tapeworms. |
| Pyrantel Salts | Pyrantel Pamoate | Small Strongyles, Pinworms, Large Strongyles (less effective) | Often given daily for a short time or used as a “power dose” for tapeworms. |
Focusing on Key Worms
When talking about equine parasite control, we focus on four main threats:
- Small Strongyles (Cyathostomins): These are the most common. Resistance to some drugs is very high in these worms.
- Large Strongyles (Bloodworms): These were once the biggest killer, but modern drugs work well against them. Still, they are dangerous if left untreated.
- Tapeworms (Anoplocephala perfoliata): These worms cause gut issues and are often missed because standard FEC tests don’t count their eggs well. You often need a specific test or use a drug known to treat them (like Praziquantel or a double dose of fenbendazole for horses).
- Pinworms (Oxyuris equi): These cause tail itching and restlessness. They are treated easily with ivermectin for horses or Pyranel.
Creating a Deworming Schedule for Horses
The correct deworming schedule for horses depends on several factors: the horse’s age, environment, health status, and FEC results.
Factors Influencing Horse Worming Frequency
Your horse worming frequency should change based on these points:
- Age: Foals and yearlings need frequent, careful treatment as their immune systems develop. Older horses sometimes need less frequent treatment if they are low shedders.
- Pasture Management: Heavily stocked pastures need stricter control. Clean up manure daily if possible.
- FEC Results: This is the biggest guide. Low shedders might only need 1–2 treatments a year. High shedders might need 3–4 treatments.
- Drug Used: Some drugs last longer than others. Moxidectin, for example, can suppress egg counts for a longer time than Ivermectin.
A Sample Targeted Schedule (Always Confirm with Your Vet)
This is a general guideline. Your vet will tailor it after reviewing your FEC results.
| Time of Year | Goal of Treatment | Drug Type Often Used | Target Worms |
|---|---|---|---|
| Early Spring (March/April) | Clear out encysted small strongyles that survived winter. | Ivermectin or Moxidectin | Small Strongyles (encysted stages) |
| Late Spring/Early Summer (May/June) | Treat based on FEC results. | Drug based on FEC category (Low/Moderate/High) | Strongyles, Ascarids (in young horses) |
| Late Summer/Early Fall (Aug/Sept) | Recheck FEC. Treat based on results. Target tapeworms if necessary. | Pyrantel (for tapeworms) or FEC-based drug | Tapeworms, Strongyles |
| Late Fall/Winter (Nov/Dec) | “Power Dose” to kill most worms before winter dormancy. | Moxidectin or Ivermectin (often combined with a tapeworm killer) | All major worms, especially encysted strongyles |
Using Broad-Spectrum Dewormers for Horses
Broad-spectrum dewormers for horses are those that kill many different types of worms at once. Most modern products are broad-spectrum.
When you use these, make sure the drug is effective against the worms common in your area. If resistance is high to one drug (like certain small strongyles resisting Ivermectin), using a product that contains two different drug classes might be necessary, or switching to a different single-drug option like Moxidectin.
Administering Dewormer Correctly
Giving the medicine the wrong way is a huge reason why treatments fail. You must ensure the horse gets the full dose and that it stays down.
How to Give Oral Paste Dewormer
Most dewormers come as paste in a plastic syringe.
- Weigh Your Horse: Always dose based on the horse’s current weight, not an estimate. Underdosing is the main cause of resistance development.
- Calculate the Dose: Read the syringe markings carefully. A 1,000 lb horse might need one full tube, but a 1,200 lb horse might need more than one tube.
- Position the Horse: Stand beside your horse’s head, not directly in front.
- Insert the Tip: Place the tip of the syringe over the back of the tongue, as far back as you comfortably can. Avoid the middle of the tongue.
- Administer Quickly: Depress the plunger firmly to squirt the paste onto the back of the tongue.
- Encourage Swallowing: Hold the horse’s muzzle slightly elevated for a few seconds. Rubbing the throat gently can help trigger swallowing.
- Monitor: Watch the horse for a few minutes to make sure it does not spit out the paste or immediately try to drink water, which can wash the drug away.
The Importance of Accurate Weight
If you use too little anthelmintic drugs for horses, the worms that are slightly harder to kill survive. These survivors then multiply, passing on their resistance genes. This is why accurate weighing is critical. Use a weight tape or, ideally, a scale for the most precise dosing.
Combating Equine Dewormer Resistance
Equine dewormer resistance is the biggest challenge in modern horse management. If you keep using the same drug over and over, the tough worms survive and thrive.
Strategies to Slow Down Resistance
Veterinarians recommend several steps to keep your dewormers effective for longer:
- Test First (FEC): Do not treat horses with low FEC scores just because it is time to deworm. This exposes the few worms they have to the drug unnecessarily.
- Rotate Drugs Wisely: Do not switch drugs every time you deworm. Rotating too often can cause resistance to build quickly in all drug classes. Instead, stick to one drug class for a specific time frame, guided by your vet and local resistance data.
- Target High Shedders: Focus your treatment efforts on the 20% of horses that shed 80% of the parasite load (the high shedders found via FEC). Low shedders need fewer treatments.
- Use Correct Dosage: As mentioned, never underdose.
- Manage the Pasture: Keep stocking rates low. Harrowing (dragging) manure helps break up parasite larvae, exposing them to the sun and drying out.
Specific Drug Use Notes
- Ivermectin for horses: This has been the go-to drug for decades. However, resistance in small strongyles is now widespread in many areas. Use it thoughtfully, perhaps only when FECs show it is still effective against the primary infection.
- Fenbendazole for horses: This drug is effective against tapeworms at a double dose (10 mg/kg for 5 days). At standard doses, it is a reliable choice for certain strongyles but less effective against encysted stages.
Beyond Chemical Control: Environmental Management
Deworming is only one part of the solution. If you put the horse back onto a contaminated field, it will get reinfected quickly. Good pasture hygiene is essential for successful equine parasite control.
Pasture Cleanliness
Parasite larvae develop best in warm, moist conditions. Reducing the parasite load in the environment lessens the need for constant deworming.
- Manure Removal: Pick up manure daily or every few days. This prevents larvae from maturing.
- Harrowing/Dragging: Dragging the pasture breaks up manure piles, exposing the inside to sunlight and drying. This kills many larvae. Do this several times during grazing season.
- Co-Graze Strategically: If possible, allow cattle or sheep to graze pastures after horses. Their digestive systems handle strongyle larvae differently, which can help “clean” the pasture.
Rotational Grazing
Rotate your horses between different fields. Allowing a field to rest for 60 to 90 days in warm weather can break the parasite life cycle. Most strongyle larvae die off after 2-3 weeks when they are not being refreshed by fresh manure. Resting the pasture starves them out.
Special Considerations for Deworming
Different horses have different needs. Foals, pregnant mares, and performance horses require special plans.
Deworming Foals and Young Horses
Foals are highly susceptible to parasites, especially Ascarids (roundworms).
- Foals: Should usually start deworming early, around 2-3 months of age, often with a product effective against roundworms.
- Yearlings and Two-Year-Olds: These horses are often moderate to high shedders and need more consistent monitoring until their immune systems mature further, usually by age three.
Pregnant and Nursing Mares
Mares should be treated carefully. You want to protect the mare and pass the fewest parasites possible to the foal via the milk. Talk to your vet about using safe, effective drugs during pregnancy. Often, a treatment is given shortly before foaling and again after weaning.
Deworming Performance Horses
These horses often travel to shows and mix with horses from other regions. This mixes parasite strains. They often need consistent control but must still be tested to avoid over-treating.
Frequently Asked Questions (FAQ) About Deworming
How often should I deworm my horse?
The horse worming frequency is no longer fixed. It should be based on your horse’s fecal egg count (FEC). High shedders might need treatment 3–4 times a year. Low shedders might only need 1–2 targeted treatments annually. Always consult your veterinarian.
Can I use human dewormer on my horse?
No, you should never use human dewormers on horses. The drugs are formulated differently, and the dosage required for a horse is much larger and often based on different active ingredients than those available over the counter for people. Using human medication can be ineffective or even toxic to your horse.
What is the best dewormer for tapeworms?
Standard dewormers often do not kill tapeworms well. The most effective treatments involve either a dose of Praziquantel or a double dose (5 times the standard amount for 5 days) of fenbendazole for horses. You must treat for tapeworms at least once or twice a year, often in the fall and spring.
Why is my horse still getting worms after deworming?
This usually happens for two main reasons: either the drug used was not effective against the specific worms present (resistance), or the horse immediately picked up new larvae from a contaminated pasture after the drug wore off. Good pasture management is as vital as the drug itself.
What is the difference between Ivermectin and Moxidectin?
Both are macrocyclic lactones. Ivermectin for horses is a standard, reliable drug, but resistance is common in small strongyles in many regions. Moxidectin (often sold as Quest) typically has a longer residual effect, meaning it keeps working inside the horse for a longer period, potentially reducing the need for frequent dosing.