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Monthly Horse Wormers: Effectiveness, Issues & Natural Alternatives

Why Dewormers Can Become Ineffective (Resistance)

Regularly deworming horses on a fixed monthly or bi-monthly schedule can lead to anthelmintic resistance – parasites evolving to survive the treatment. Overusing the same drug class repeatedly kills off susceptible worms, leaving only the resistant ones to reproduceextension.psu.eduextension.psu.edu. Over time, these resistant parasites dominate, and the dewormer no longer works well on your farmextension.psu.eduextension.psu.edu. This is why the old practice of dosing every 6–8 weeks is now discouragedextension.psu.edu. In many regions, small strongyles have already developed widespread resistance to certain dewormer classes (e.g. benzimidazoles)extension.psu.eduextension.psu.edu. To slow resistance, experts recommend targeted deworming based on fecal egg counts and rotating classes only when neededextension.psu.eduextension.psu.edu. Maintaining a refugia (a population of parasites not exposed to chemicals) by not over-worming all horses helps preserve drug efficacyextension.psu.eduextension.psu.edu. In short, using dewormers too frequently or incorrectly can make them non-effective by breeding “super worms” that our treatments can’t kill.

What to Do If There’s No Improvement After Deworming

If you’ve given a dewormer and your horse still doesn’t improve (e.g. coat still poor, weight low, or you *continue seeing signs of worms), don’t just keep blindly giving more wormer. First, ensure the dewormer was given properly – correct dosage for the horse’s weight and that the full dose was swallowed (some horses spit out paste)ssequineclinic.comssequineclinic.com. Under-dosing or improper administration can leave worms alive. Next, perform a Fecal Egg Count Reduction Test (FECRT) about 10–14 days after dewormingtvmdl.tamu.edussequineclinic.com. Have a fecal sample checked for parasite eggs; you should see at least a 90–95% drop in egg count if the dewormer was effectivetvmdl.tamu.edu. If the fecal egg count is still high (only a minimal reduction), it indicates the worms on your farm might be resistant to that drugssequineclinic.comssequineclinic.com. In that case, switch to a different class of dewormer (for example, if worms resisted ivermectin, try a benzimidazole or pyrantel next) and then re-check fecal eggs again in 2 weeksssequineclinic.comssequineclinic.com. Involving your veterinarian is wise – they can help interpret results and choose an effective product. Also consider that the problem might not be worms at all: poor coat or weight could be due to nutrition or illness. So, if deworming made no difference and fecal tests are low, work with a vet to investigate other causes rather than repeatedly deworming unnecessarily.

Reasons You May Not See Worms (or Changes) in Manure or Coat

It’s actually unusual to see visible worms in horse manure after deworming, so don’t be alarmed if you don’t see parasites in the feceswestgatelabs.co.uk. Most common equine worms are small or are digested after being killed, so they rarely appear obviously in the stoolwestgatelabs.co.ukwestgatelabs.co.uk. For example, strongyle eggs and larvae are microscopic and not visible to the naked eyewestgatelabs.co.uk. Large roundworms (Parascaris) might be seen in foals’ droppings if they had a heavy infestation, but in adult horses it’s infrequentwestgatelabs.co.ukwestgatelabs.co.uk. If you don’t see worms being “passed,” it could simply mean the dewormer worked and the parasites were eliminated at a microscopic level, or that your horse didn’t have a high worm load to begin with. Similarly, a horse’s coat might not instantly become sleek (“slick off”) after worming – especially if worms were not the main cause of a dull coat. In young horses, a heavy parasite burden can cause a poor, rough hair coat and potbellypetmd.com, and effective deworming should gradually improve overall condition. But if an adult horse doesn’t shed its shaggy coat in spring despite deworming, consider non-parasitic causes. Equine Cushing’s disease (PPID) is a common reason for failure to shed the winter coatvetmed.tamu.eduvetmed.tamu.edu. Other factors like nutrition, age, and season play roles too. In short, lack of visible worms in manure is usually normal, and a persistently rough coat might hint at something like PPID or dietary issues rather than an ineffective wormer.

 

Large roundworms (Parascaris equorum) visible in a foal’s manure. These spaghetti-like worms (up to 30 cm long) are roundworms, typically seen in young horses with heavy infections. It’s rare to find such worm masses in adult horse droppings – most internal parasites in adult horses are smaller strongyles or tapeworms that do not appear visibly in manure (their eggs are microscopic)westgatelabs.co.ukwestgatelabs.co.uk. If you do see worms like this, ensure you identify them and use an appropriate dewormer targeting that parasite.

Natural Deworming Remedies (Non-Chemical Options)

Some horse owners seek natural alternatives to chemical dewormers due to concerns about overuse or toxicity. It’s important to approach these with realistic expectations – many natural remedies have limited scientific evidence of effectiveness. Below are some common natural or holistic worming approaches:

  • Diatomaceous Earth (DE): A fine powder made of fossilized algae, often fed in hopes of cutting or dehydrating worms. While DE can kill insects in dry environments, it doesn’t work inside a wet gutequisearch.com. The horse’s intestines are moist, rendering DE ineffective at cutting worms’ exoskeletonsequisearch.com. Studies in livestock have found no significant worm reduction from feeding DEequisearch.com. Additionally, dry DE is a respiratory irritant, so pouring the powder can cause horses (and humans) to inhale particlesequisearch.com. Bottom line: DE is natural but not proven to control internal horse parasites.

  • Herbal Dewormers: Various herbs (such as wormwood, wormseed, black walnut, clove, garlic, fennel, etc.) are ingredients in herbal worming blends. Some herbs do have antiparasitic compounds – for example, wormwood contains thujone, and pumpkin seeds contain cucurbitacin – but the doses required to kill worms are extremely high and often border on toxic for the horseequisearch.comequisearch.com. Wormwood and related herbs can cause serious nervous system and organ toxicity at effective dosesequisearch.com. Pumpkin seeds would require feeding several pounds per day to have deworming effectequisearch.com, which is impractical. More benign herbs like garlic, anise, and sage are sometimes given daily for general health, and while they may have minor antiparasitic properties, their effect is likely too small to replace true dewormersequisearch.com. In practice, herbal products might slightly reduce worm loads but likely won’t clear a significant infection – and improper use could harm the horse. Always consult an equine herbal specialist or veterinarian before using high-dose herbal remedies.

  • Biological Control (Nematode-Trapping Fungi): A newer natural approach is using a fungus called Duddingtonia flagrans, formulated in products like BioWorma®. This fungus passes through the horse and into the manure, where it traps and consumes worm larvae as they hatch, reducing pasture contaminationbioworma.com. BioWorma is fed daily as a supplement (often mixed into feed) and can dramatically cut down the number of infective larvae in the feces and pasture. It’s not a direct dewormer (it doesn’t kill worms inside the horse), but it breaks the lifecycle by preventing reinfection on pasturebioworma.combioworma.com. For owners who eschew chemical dewormers, BioWorma offers a way to naturally curb parasites in the environment. Keep in mind it’s most useful as part of an integrated parasite management plan – for example, alongside manure removal and occasional targeted deworming – rather than a standalone solution, especially for horses with active infections.

  • Pasture Management and Other Practices: Managing the horse’s environment is a key “natural” way to reduce parasite burdens. Regularly picking up manure from paddocks (at least 2–3 times a week) prevents worm eggs and larvae from spreadingssequineclinic.com. Rotating pastures and avoiding overgrazing (so horses aren’t eating near their own manure) can lower ingestion of larvae. Some grazing strategies involve rotating other species (like sheep or cattle) through horse pastures, since most equine parasites are species-specific. Additionally, ensuring horses have good nutrition and overall health will help their immune system naturally resist parasites. Copper and zinc levels in the diet, for example, are thought to influence parasite resistance, and some holistic programs include supporting the horse’s immune health so that it can tolerate a small worm burden without issues. While these management steps aren’t dewormers per se, they reduce reliance on chemical wormers and support any natural or conventional program.

Important: If you opt for natural remedies, monitor your horse’s parasite status with fecal egg counts regularly. Many alternative treatments have not been scientifically proven to effectively eradicate internal parasites in horsesequisearch.com. You may find a reduced egg count if a natural method is helping – or you may find it unchanged, indicating the need for a conventional dewormer to prevent health issues. Severe infestations of worms can cause colic, weight loss, anemia, and permanent organ damage to your horsetvmdl.tamu.edutributeequinenutrition.com, so don’t gamble with your horse’s health. Use natural approaches as supportive measures, but be ready to treat with an FDA-approved dewormer if evidence shows it’s necessary.

Recommended Deworming Products (U.S. Brands & Links)

When using commercial dewormers, it’s best to rotate among different classes strategically and dose appropriately. Here are some common U.S. equine dewormer products and what they target (with links to where you can find them):

  • Ivermectin 1.87% Paste – Broad-spectrum against large/small strongyles, pinworms, ascarids, bots, etc. (Does not kill tapeworms). Example products: Durvet DuraMectin Paste (ivermectin) – available at Amazon and Valley Vet. Safe for all horses including pregnant maresvalleyvet.com. Typically given spring and fall to target bots after those seasons.

  • Moxidectin 2% Gel – A powerful dewormer (macrocyclic lactone class like ivermectin) effective against encysted small strongyle larvae as well as bots and other worms. Often sold as Quest® Gel. Use with caution in foals or minis due to narrower safety margin. Available at Amazon and Valley Vet (Zoetis Quest Gel). Note: Moxidectin is usually given once a year (often late winter/early spring) because it can target encysted strongyles that other drugs missssequineclinic.com. Do not use concurrently with other macrocyclic lactones.

  • Fenbendazole 10% Paste – Benzimidazole class dewormer. Effective against large and small strongyles, pinworms, and ascarids; safe for foals. Brand names include Panacur® or Safe-Guard®. Standard single dose, or the Panacur PowerPac (double dose for 5 days) to eliminate encysted strongyles. Available at Amazon (various sellers) and Valley Vet (Panacur paste). Note: Widespread resistance of small strongyles to fenbendazole existsextension.psu.edu, so it’s most useful for ascarids in foals or when a fecal test shows it’s still effective on your farm. Always dose by accurate weight; under-dosing increases resistancessequineclinic.com.

  • Pyrantel Pamoate Paste – Tetrahydropyrimidine class. Good for large strongyles, small strongyles, roundworms, and pinworms. Commonly known as Strongid® Paste. Safe for pregnant mares and young horsesvalleyvet.com. A double dose of pyrantel is also one approved method to treat tapeworms (two tubes at once for an average horse). Available at Amazon and Valley Vet (Strongid paste by Zoetis). Additionally, pyrantel tartrate is sold as a daily feed-through (e.g. Strongid C 2X pellets Valley Vet), which is given in feed daily to kill ingested larvae – however, daily dewormers have fallen out of favor due to resistance concerns (constant low dosing can select for resistant worms).

  • Ivermectin + Praziquantel Combination – Broad-spectrum plus specific tapeworm control. Products like Equimax® (1.87% ivermectin + 14.03% praziquantel) or Zimecterin Gold® target everything ivermectin does and tapeworms. Often used in late fall after the first frost, to nail bots and tapeworms before winter. Example: Equimax Paste – available at Amazon and Valley Vet. Praziquantel is very effective against Anoplocephala tapeworms that other drugs missvalleyvet.comvalleyvet.com. Use combo products only once or twice a year as needed (e.g. end of grazing season) to reduce resistance risk.

  • Moxidectin + Praziquantel Combination – Quest Plus® is moxidectin with added praziquantel, covering encysted small strongyles, bots, and tapeworms all in one dose. Often recommended for late grazing season (fall) in adult horses. Available at Amazon and Valley Vet (Quest Plus gel). Because it’s potent, ensure accurate dosing by weight and do not use in foals under 6 months. One fall dose per year is usually sufficient if your fecal monitoring indicates it’s needed.

  • Natural/Alternative Products: If you prefer to incorporate natural methods, you can find some products marketed for that purpose. For example, BioWorma® feed supplement (Duddingtonia fungus) can be purchased in the U.S. (often in 5 lb or 15 lb pails) – see Amazon for a 15 lb pasture supplement. Herbal blends for horses (containing things like wormwood, cloves, etc.) are sold by certain companies, but use them cautiously. One such product is Silver Lining Herbs “Herbal Wormer” (#13) – available from the manufacturer and some equine supply sites. Food-grade Diatomaceous Earth is widely sold (e.g. Amazon) for those who want to try it as a feed additive, but remember the scientific consensus that it likely won’t harm worms internallyequisearch.comequisearch.com. Always confirm any natural program’s efficacy with fecal tests.

Lastly, whatever product you use, rotate intelligently and dose correctly. Base your worming calendar on your horse’s needs: young horses (<3 years) require more frequent deworming (they are more vulnerable to ascarids and strongyles), whereas healthy adult horses may only need deworming 1–3 times a year if they have consistently low egg countsssequineclinic.com. Use fecal egg counts to identify “high shedders” who might need more frequent treatment, and let low-shedding horses be part of your refugia (getting dewormed less often)extension.psu.eduextension.psu.edu. This strategy will help keep all these dewormer products effective for years to come, while keeping your horse healthy and parasite-free.

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