What is the best way to worm a horse? The best way to worm a horse is by using a targeted approach based on fecal egg count testing results and veterinarian advice, rather than sticking to a fixed, routine schedule. This modern method ensures you use the best horse dewormer only when needed, which helps slow down parasite resistance.
The Shift in Modern Equine Parasite Control
For many years, horse owners followed a strict deworming schedule for horses. This meant giving a dewormer every few months, no matter what. This old method had a big problem: it caused serious resistance in common horse worms. Today, veterinary experts promote equine parasite control based on testing. This means testing the horse first. Then, the vet suggests the right anthelmintic treatment for horses. This targeted plan keeps horses healthy. It also makes the deworming drugs last longer.
Why Routine Deworming Fails
Routine deworming kills the weak worms. The few strong worms survive. These strong worms breed. Soon, most worms in the horse are strong. They do not die from the standard drugs. This is called drug resistance.
Table 1: Common Worm Types and Their Risks
| Worm Type | Primary Risk | Main Concern with Resistance |
|---|---|---|
| Small Strongyles | Weight loss, colic | Most common; high resistance |
| Large Strongyles | Severe gut damage, blockages | Less common now due to old drugs |
| Tapeworms | Colic, gut irritation | Hard to test for; often missed |
| Pinworms | Tail rubbing, skin irritation | Affects horse comfort and behavior |
Step 1: Recognizing the Signs of Worms in Horses
You must know the signs of worms in horses. Seeing these signs means the parasite load is already high. Early detection helps prevent serious health issues.
Physical Indicators of a Heavy Worm Load
Look closely at your horse’s body. A heavy worm burden causes visible changes.
- Poor coat quality. The hair looks dull or rough.
- Unexplained weight loss, even with good food.
- Diarrhea or soft manure.
- A pot-bellied appearance, especially in younger horses.
- Lethargy or low energy levels.
- Chronic, low-grade colic episodes.
- Poor performance in working horses.
Sometimes, internal damage is severe before you see any clear outward signs. This is why testing is so important.
Step 2: Fecal Egg Count Testing Explained
Fecal egg count testing (FEC) is the key to smart parasite control. A veterinarian or lab checks a manure sample. They count how many worm eggs are present. This number tells you if the horse needs deworming. It also tells you how heavy the infestation is.
How FEC Testing Works
- Collect the Sample: Collect fresh manure. Usually, you need about two tablespoons from several fresh droppings. Keep it cool, but do not freeze it. Get it to the lab quickly.
- Lab Processing: The lab mixes the manure with a special solution. This helps separate the eggs.
- Counting: They view the sample under a microscope. They count the eggs per gram (EPG) of manure.
Interpreting EPG Results
Vets use the EPG count to sort horses into groups. This grouping helps decide the deworming schedule for horses.
| EPG Category | Description | Recommended Action |
|---|---|---|
| Low Shedder (0–200 EPG) | Fewest eggs passed. | Deworm only for specific threats (like tapeworms). Focus on pasture management. |
| Moderate Shedder (201–500 EPG) | Average parasite load. | Targeted deworming as advised by vet, usually 2-3 times per year. |
| High Shedder (>500 EPG) | Heavy parasite burden. | Treat aggressively with the correct drug based on FEC results. |
Low shedder horses are crucial. They shed very few eggs onto the pasture. Treating only high shedders saves drug use for those who need it most.
Step 3: Choosing the Right Dewormer
Once you know the parasite level, you must pick the right medicine. There are several types of dewormers available. Using a broad spectrum horse dewormer is sometimes necessary, but often, targeted treatment is better.
Types of Active Ingredients
Modern anthelmintic treatment for horses uses drugs that kill specific types of worms.
- Macrocyclic Lactones (Moxidectin and Ivermectin): These are strong and kill many worms, including bots. Moxidectin lasts longer than Ivermectin.
- Benzimidazoles (Fenbendazole and Albendazole): These are effective against some small strongyles. They are often used for tapeworm treatment, though effectiveness varies.
- Pyrantel (Pyrantel Pamoate): Often used for tapeworms and pinworms. It has a short contact time, so it must be given in a full dose.
Selecting the Best Horse Dewormer
The best horse dewormer changes based on local resistance patterns. Your local vet knows which drugs still work well in your area.
Important Note on Tapeworms: Standard FEC tests do not reliably find tapeworm eggs. Many vets suggest treating for tapeworms once or twice a year, often in the fall and spring, using products containing Pyrantel or a double dose of Fenbendazole.
Step 4: Rotating Horse Dewormers Safely
To slow resistance, rotating horse dewormers is a common practice. This means switching the type of drug used at different times of the year. This confuses the worms. It stops them from developing resistance to just one type of drug.
Creating a Rotation Plan
A simple rotation plan involves using drugs from different chemical classes throughout the year. Always consult your vet for a plan specific to your farm’s FEC history.
Example Rotation Strategy (Consult Vet First):
- Spring Treatment (March/April): Use a Macrocyclic Lactone (like Moxidectin) combined with a drug for tapeworms.
- Summer Treatment (July/August): Use a Benzimidazole (like Fenbendazole).
- Fall Treatment (October/November): Use another Macrocyclic Lactone (like Ivermectin) or the other Moxidectin if you used Ivermectin in Spring. This is often when you treat for bots again.
- Winter Treatment (January/February): No routine treatment unless FEC is high or tapeworm treatment is due.
This strategy ensures that different worm populations are targeted at different times.
Step 5: Effective Administration of Dewormers
Giving the right dose is as important as choosing the right drug. Too little medicine will fail to kill the worms, promoting resistance. Too much is wasteful and stresses the horse.
How to Administer Paste Dewormer
Most dewormers come as a paste in a large syringe. Proper administering paste dewormer ensures the horse gets the full dose.
- Weigh Your Horse: Always dose based on the horse’s current weight. Underdosing is common because people guess the weight. Use a weight tape or weigh scale.
- Prepare the Dose: Twist the dial on the syringe to the weight mark.
- Application: Open the horse’s mouth. Place the tip of the syringe as far back on the tongue as possible, near the base.
- Encourage Swallowing: Quickly depress the plunger, depositing the paste on the back of the tongue. Immediately raise the horse’s head slightly. Stroke their nose or lightly blow on their nostrils. This encourages them to swallow rather than spitting it out.
- Wait: Do not let the horse eat or drink for 30–60 minutes after administering paste dewormer. This allows the medicine to move fully through the digestive tract.
Dosing for Specific Parasites
Sometimes, standard doses do not work well for certain worms.
- Tapeworms: Many vets suggest a double dose of Fenbendazole or using a Pyrantel product, as these target tapeworms better.
- Bots: Ivermectin and Moxidectin are highly effective against bot larvae. Treatment should happen after the first hard frost, usually late fall, to kill those ingested during the summer.
Step 6: Managing Horse Parasites Through Environment Control
Managing horse parasites is not just about drugs. It involves keeping your pastures clean. A clean environment reduces the number of larvae horses eat daily. This is vital for long-term health and reducing the need for frequent deworming.
Pasture Management Techniques
The larvae of strongyles primarily live in the first few inches of grass. Keeping grass short means horses eat more larvae.
- Manure Removal: Pick up manure daily or every other day. This removes the eggs before they hatch into infective larvae.
- Rotational Grazing: Move horses frequently to fresh pasture. This gives contaminated pastures time to “rest.” Sunlight and time kill most larvae. A rest period of 60–90 days in hot weather is very helpful.
- Mowing and Harrowing: Mow fields when grass is long to keep it short. Harrowing (dragging) breaks up manure piles, exposing the larvae to the sun, which kills them. Be careful with harrowing if the ground is very dry, as this can spread eggs over a wider area.
- Use of Larvicide (Use Sparingly): In severe cases, veterinary-approved pasture sprays can kill larvae on the grass. This is a very specialized treatment and should be used carefully.
Managing High Shedders
If you have high EPG horses, they pose the biggest threat to your pasture.
- Keep high shedders quarantined to a sacrifice lot or small paddock.
- Clean this high-risk area daily.
- Treat these horses aggressively based on FEC results.
Step 7: Post-Treatment Testing (Fecal Egg Re-Check)
After you treat a horse, you need to know if the treatment worked. This is called a Fecal Egg Re-Check (FER).
When to Re-Check
Wait about 10–14 days after administering paste dewormer. This gives the drug time to clear the system. Then, submit a new manure sample.
- If the EPG count dropped significantly (e.g., from 1000 EPG to under 100 EPG), the treatment was successful.
- If the EPG count remains high, the horse might have resistant worms, or the dosing was incorrect. You may need to try a different drug class.
This feedback loop is the core of effective equine parasite control. It ensures you are not wasting money on drugs that do not work for your herd.
Safety Precautions When Deworming
Handling dewormers requires care. These are powerful medicines.
Protecting Yourself and Your Horse
- Wear Gloves: Always wear disposable gloves when administering paste dewormer. Some dewormers can be absorbed through the skin. Wash your hands well afterward.
- Store Properly: Keep dewormers in a cool, dry place, away from pets and children. Check expiration dates.
- Avoid Contamination: Do not let the tip of the dewormer tube touch the horse’s mouth. Contamination can cause the horse to refuse the next dose.
- Accurate Dosing is Key: Never use a drug meant for a 1,000 lb horse on a 500 lb pony. Always dose by weight.
Special Considerations in Equine Parasite Control
Different horses have different needs. A one-size-fits-all approach to managing horse parasites fails.
Foals and Weanlings
Young horses are very susceptible to worms. They often need a more consistent treatment plan until they mature.
- Foals often need treatment for roundworms early on.
- Foals usually start deworming around 6–8 weeks of age, based on vet advice.
- They are usually re-tested more frequently than adult horses.
Older and Immunocompromised Horses
Senior horses or those with weakened immune systems may carry higher parasite loads easily. They might need more frequent testing and treatment, even if they are typically low shedders.
New Horses
Any new horse arriving at your farm must be quarantined. Test their manure immediately. Treat them based on FEC results before introducing them to your main herd. This prevents bringing drug-resistant worms onto your clean pastures.
Frequently Asked Questions (FAQ) About Deworming
How often should I worm my horse?
This depends on the fecal egg count testing results. Most healthy adult horses with low EPG counts only need deworming 2 to 3 times a year. High shedders may need treatment more often, guided by their vet.
Is there a dewormer that kills everything (a true broad spectrum horse dewormer)?
No single drug kills every parasite perfectly, especially tapeworms and encysted small strongyles. Most modern products are very broad, but you often need to combine treatments or rotate drugs to cover all bases.
My horse refuses to swallow the paste. What should I do?
If you suspect the horse spat out the paste, you must re-dose them. Try administering paste dewormer again after 30 minutes. Next time, try mixing the dewormer into a small amount of palatable feed, like molasses or apple sauce, and feed it quickly.
What is the best time of year for deworming?
Generally, treat in the late spring and again in the late fall. The fall treatment targets encysted larvae before they emerge in the winter, and the spring treatment cleans out worms before the primary grazing season begins.
Do I still need to treat for bots?
Yes. Even with good equine parasite control, bot flies are common. Treat for bots in the late fall after the first few frosts, using an Ivermectin or Moxidectin product.
Can I use a feed additive dewormer?
Some products are mixed into feed daily. While convenient, these often result in underdosing, which is a major driver of resistance. They are not usually recommended as the main form of anthelmintic treatment for horses. Targeted paste treatment remains the gold standard.