Why Ivermectin Is a Staple in Equine Parasite Control
Ivermectin has been a cornerstone of equine parasite management for decades. It's broad-spectrum, highly effective, and well-tolerated by horses of all breeds and sizes. Whether you're managing a single backyard horse or a large herd, understanding how ivermectin works — and how to use it correctly — is essential for keeping your animals healthy.
What Does Ivermectin Treat in Horses?
Ivermectin is effective against a wide range of internal and external parasites, including:
- Large strongyles (bloodworms) — including arterial stages of Strongylus vulgaris
- Small strongyles (cyathostomins) — adult stages; does NOT kill encysted larvae
- Roundworms (ascarids) — effective in foals and young horses
- Pinworms (Oxyuris equi)
- Hairworms (Trichostrongylus axei)
- Large-mouth stomach worms (Habronema spp.)
- Bots (Gasterophilus spp.) — oral and gastric stages
- Lungworms (Dictyocaulus arnfieldi)
- Neck threadworms (Onchocerca spp.) — microfilariae
What ivermectin does NOT treat: Tapeworms (require praziquantel) and encysted small strongyle larvae (require moxidectin or a 5-day fenbendazole course).
Ivermectin Formulations for Horses
Ivermectin for horses is available in several forms:
- Oral paste (most common) — administered via a syringe directly into the mouth; easy to use and widely available
- Oral gel — similar to paste, slightly different consistency
- Combination products — ivermectin + praziquantel (for tapeworm coverage) is a popular combination for fall deworming
Dosing Ivermectin for Horses
The standard dose of ivermectin for horses is 200 mcg per kg of body weight (0.2 mg/kg). Most paste formulations are pre-measured for a 1,250 lb horse, with a dial or weight markings on the syringe.
How to dose correctly:
- Weigh your horse accurately — use a weight tape if a scale isn't available
- Set the syringe dial to your horse's weight
- Administer the paste to the back of the tongue
- Hold the horse's head up briefly to ensure swallowing
- Check that the horse doesn't spit out the paste
Never underdose. Giving less than the correct dose is one of the leading causes of anthelmintic resistance.
When to Use Ivermectin
Ivermectin is most commonly used:
- Spring: After the last frost, to treat parasites that became active over winter
- After bot fly season (late fall/early winter): To eliminate bot larvae that were ingested during the season
- As needed: Based on fecal egg count results for moderate and high shedders
For tapeworm coverage, use an ivermectin + praziquantel combination product at least once a year, typically in fall.
Is Ivermectin Safe for All Horses?
Ivermectin is generally very safe for horses when used at the correct dose. However, keep these considerations in mind:
- Foals: Safe for foals as young as 4 weeks old
- Pregnant mares: Considered safe; consult your vet for specific guidance
- Debilitated horses: Use with caution and veterinary guidance in severely ill or malnourished horses
- Miniature horses and donkeys: Dose carefully by weight — these animals are often overdosed when treated like full-sized horses
Important: Never use equine ivermectin products in other species without veterinary guidance. Ivermectin is toxic to some dog breeds (particularly Collies and related breeds with the MDR1/ABCB1 gene mutation) at certain doses.
Resistance Concerns
Ivermectin resistance in small strongyles is increasingly common. To help preserve its effectiveness:
- Use fecal egg counts to guide treatment decisions rather than treating on a fixed schedule
- Perform fecal egg count reduction tests (FECRT) periodically to confirm efficacy
- Rotate between drug classes (macrocyclic lactones like ivermectin/moxidectin, benzimidazoles, and pyrimidines) based on resistance patterns
- Never underdose
Ivermectin vs. Moxidectin: Which Should You Use?
Both ivermectin and moxidectin are macrocyclic lactones with similar spectrums of activity, but there are key differences:
- Moxidectin has a longer residual activity and is effective against encysted small strongyle larvae — making it the preferred choice for fall deworming
- Ivermectin is the better choice for foals and young horses, as moxidectin is not recommended for foals under 4 months
- Both are effective against bots and most adult strongyles
Shop Equine Dewormers at Paw and Tail Supply
We carry ivermectin paste, ivermectin + praziquantel combinations, moxidectin, and other equine dewormers to support your horse's year-round parasite control program. Fast shipping so your horses get what they need when they need it.
