Common Horse Parasites & Deworming Guide — from one tack room to another

I’ll never forget the smell of wet hay and diesel the morning I realized my mare, Lottie, had been losing weight for no obvious reason — dull coat, itchy tail, and that hollow sound when she moved. I’d assumed pasture was “safe” because she looked bright the week before. Turns out the problem was invisible to the eye: parasites. That day taught me that good horsemanship is part detective work, part routine, and—sometimes—humble apologies to your veterinarian.

Why parasites matter (and how they sneak up on you)

Parasites range from the tiny strongyle egg you won’t notice on a dirty paddock, to the dramatic colic from a heavy ascarid burden in foals. Most horses tolerate a low-level burden — but pasture contamination, herd density, and the wrong treatment at the wrong time let populations explode. You may see weight loss, poor coat, intermittent colic, tail rubbing (pinworms), or bots stuck in the mouth—little clues that add up. The key is not to panic, but to be strategic.

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The modern approach: test, don’t just rotate blindly

Years ago people rotated dewormers like clockwork. Now the smart move is to use fecal egg counts (FECs) to stratify horses into low, medium, and high shedders — then treat accordingly. Do a baseline FEC once or twice a year and use fecal egg count reduction tests (FECRTs) occasionally to confirm your dewormer is still working for your barn. This approach reduces pasture contamination and slows resistance. These ideas are central to updated AAEP guidance. 

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Common culprits (what you’ll actually fight)

• Strongyles (large and small) — the usual suspects; can cause weight loss and poor performance.

• Ascarids — big problem in foals and weanlings; can cause intestinal blockage if you deworm improperly.

• Tapeworms — often silent but linked to spasmodic colic; need a cestocide (praziquantel) to conquer.

• Bots — those crunchy larvae in the stomach; treat with an ivermectin or moxidectin product in late fall/early winter.

An effective plan usually includes a cestocide (praziquantel) for tapeworms and a boticide (ivermectin or moxidectin) at appropriate times. Merck and veterinary references outline these standard recommendations. Merck Veterinary Manual

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My mistakes (so you don’t repeat them)

1. Blind rotation: I once alternated products every 8 weeks because “that’s what my neighbor did.” Result: I created low-level resistance in my herd and paid for more vet visits. Lesson: test first.

2. Under-dosing: Guessing the horse’s weight because a tape measure is “too much hassle” once cost me — underdosing selects for resistant worms. Always weigh or weigh tape accurately.

3. Treating the wrong age: Using adult protocols on foals can cause severe reactions (and even colic). Treat foals carefully and follow age-specific schedules. Veterinary guidance is gold here.

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Practical, hands-on routine I use (you can adapt)

• Spring: FEC on all horses. Target high shedders; treat only those above threshold or as your vet advises.

• Late summer/fall: Consider a boticide (ivermectin or moxidectin) once pasture risk increases.

• Autumn/winter: Target tapeworms with a praziquantel-containing product before horses are put into heavier grazing rotations.

• Always: weigh, document, and keep a treatment log — date, product, dose, lot number. The AAEP recommends using FECs and FECRTs to guide frequency. AAEP

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Products I’ve relied on (realistic picks)

• Panacur (fenbendazole) — good for ascarids and some strongyles; comes as a paste or PowerPac. I’ve used it in a pinch for foals with vet direction

• EquiMax (ivermectin + praziquantel paste) — one-dose combo that covers strongyles, bots, and tapeworms; handy in autumn. (Commonly sold on retailers like Amazon/Tractor Supply). 

Note: availability varies by country — always check local vet regulations and product approvals.

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Feeding & supplements that help resistance and recovery

Good nutrition strengthens immunity. I prefer a hay-first diet, then a ration balancer if the horse needs calories but not grain. For borderline-weight horses, Purina or Triple Crown feeds have been reliable where I boarded — but in dusty, summer paddocks I added a digestive support probiotic (look for equine-specific blends) to help gut health after deworming. Salt/mineral blocks, regular dental care, and clean water are simple steps with big returns.

It would be even better if manufacturers included easy-to-read dosing charts by weight and clearer guidance for foals vs adults — especially for combination products. A small addition like a built-in weight guide on packaging would save a lot of guesswork.

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Pasture management — the underrated weapon

• Pick manure daily if you can — it makes a huge difference in pastures with high usage.

• Alternate grazing with other species (sheep/goats) if practical — different hosts break parasite life cycles.

• Avoid overstocking and keep pasture height above 3–4 inches to minimize grazing of infective larvae. These nonchemical steps are recommended alongside deworming. 

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Seasonal & regional notes

• In warm, humid regions (think southern climates) larval stages survive longer — you’ll need more vigilance through winter.

• In dry, cold climates, transmission is seasonal — focus treatments on spring and fall peaks.

• Some breeds (like hardy native breeds on extensive grazing) can be lower shedders; performance breeds in heavy training may need closer monitoring.

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A couple of sensory memories (because horses are sensory creatures)

I remember scraping bot casings off a foreleg with that salty-dust smell of fall; Lottie’s coat went from dull to slightly oily after a heavy worm burden, and her breath had that faint dark hay scent you only notice when you’re close. Small things — a sticky tail, a flinch when you groom — gave me early warnings.

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It would be even better if…

Manufacturers offered smaller, clearly labeled doses for ponies and minis (too many of our group doses are mostly for large horses), and if vet clinics included a simple FEC package with the first consult for new owners. Small changes — big impact.

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Quick takeaways

• Test before you treat — FECs are your friend. 

• Targeted treatment is better than blind rotation. 

• Pasture management + correct dosing + good nutrition = fewer problems. 

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FAQs (short and informal)

Q: How often should I deworm?
A: Do FECs once or twice a year to stratify horses; treat high shedders more often and low shedders minimally. Vets will help set thresholds. 

Q: Can I use dog dewormer on my pony?
A: No. Different species, different doses, different formulations. Don’t risk it.

Q: My foal coughed and had worms on feces — what now?
A: Call your vet. Foals need age-appropriate deworming (e.g., benzimidazoles at set ages) and monitoring. 

Q: Any home remedies?
A: Pasture management, rotational grazing, and clean water help — but there’s no substitute for proven anthelmintics and vet guidance.