Ivermectin for Animals: Common Uses and Safety Tips in Veterinary Care

Ivermectin is one of the most widely used medications in veterinary medicine. It’s not flashy, it doesn’t come in fancy packaging, and you won’t see ads for it on TV. But if you’ve ever owned a dog, horse, goat, or even a chicken, chances are you’ve relied on ivermectin to keep your animal healthy. It’s cheap, effective, and has saved countless lives - but only when used correctly.

What Is Ivermectin and How Does It Work?

Ivermectin is a broad-spectrum antiparasitic drug derived from a soil bacterium called Streptomyces avermitilis. It was first developed in the 1970s and earned a Nobel Prize in 2015 for its role in fighting river blindness in humans. In animals, it works by paralyzing and killing parasites - especially worms, mites, and lice - by overstimulating their nervous system.

It doesn’t just kill adult parasites. It also stops larvae from developing, which is why it’s so effective for long-term parasite control. Unlike some treatments that only target one type of bug, ivermectin hits a wide range: heartworms in dogs, mange mites in cats, internal worms in goats, and even lice in cattle.

Common Uses in Different Animals

Every species reacts differently to ivermectin. What’s safe for a horse can be deadly for a dog - especially certain breeds.

• Dogs: Used to prevent heartworm disease (as part of monthly preventatives like Heartgard). Also used off-label to treat sarcoptic mange and demodectic mange. Dosage varies: heartworm prevention uses micrograms per kg, while mange treatment may require 10-100 times more.
• Cats: Rarely used due to sensitivity. Sometimes given for ear mites or mange, but only in very low, carefully calculated doses. Many vets avoid it entirely and use safer alternatives like selamectin.
• Horses: A staple in deworming programs. Effective against roundworms, bots, and pinworms. Often given as a paste every 6-12 weeks, depending on climate and pasture conditions.
• Goats and Sheep: Used for gastrointestinal worms and lice. Often given orally or by injection. Resistance is a growing problem, so rotation with other dewormers is recommended.
• Poultry: Used off-label for mites and lice. Applied topically or mixed in water. Not approved for food-producing birds in many countries, so withdrawal periods must be strictly followed.
• Rabbits and Rodents: Used cautiously for mites. Too high a dose can cause neurological damage or death.

Dosage Matters - Too Much Can Kill

One of the biggest mistakes pet owners make is using human ivermectin or livestock formulations on small animals. A single drop of horse paste can be lethal to a small dog.

For example:

• A 5 kg dog needs about 0.1 mg/kg for heartworm prevention - that’s 0.5 mg total.
• A single 1.87% horse paste tube contains 136 mg of ivermectin - enough to kill 270 dogs of that size.

Even within breeds, sensitivity varies. Collies, Australian Shepherds, Shetland Sheepdogs, and other herding breeds often carry a genetic mutation (MDR1 gene) that makes them unable to properly clear ivermectin from their brains. This can lead to severe neurological toxicity: tremors, blindness, coma, even death.

Always test for the MDR1 mutation before using ivermectin on these breeds. Many vets now skip ivermectin entirely and use moxidectin or milbemycin for heartworm prevention in sensitive dogs.

Side Effects and Risks

When used correctly, ivermectin is very safe. But overdoses or misuse can cause serious problems:

• Loss of coordination
• Excessive drooling
• Blindness or dilated pupils
• Seizures
• Coma or death

These signs usually show up within hours of an overdose. If your pet shows any of these symptoms after ivermectin use, get to a vet immediately. There’s no antidote, but supportive care - IV fluids, temperature control, and monitoring - can save lives.

Another risk: using expired or improperly stored ivermectin. Heat and moisture break down the active ingredient. A degraded product might not work at all, leaving your animal vulnerable to parasites - or it might become unpredictable in potency.

Resistance Is Real

Parasites are getting smarter. In goats, sheep, and horses, some worm populations have developed resistance to ivermectin. This isn’t because the drug is weak - it’s because it’s been overused.

Many farmers and backyard animal owners deworm on a fixed schedule, like clockwork, whether their animals have worms or not. That’s a recipe for resistance. Instead, use fecal egg counts to test for parasites before treating. Only deworm animals that actually need it. Rotate drug classes - use benzimidazoles or levamisole alongside ivermectin to slow resistance.

In Australia, where pasture-based livestock is common, resistance is already widespread in some regions. Vets now recommend targeted selective treatment rather than blanket deworming.

What to Avoid

Don’t use:

• Human ivermectin tablets for animals - concentrations are wrong and fillers can be toxic
• Leftover livestock injectables for pets - too concentrated, wrong route of administration
• Online "natural" ivermectin alternatives - no evidence they work
• Extra doses "just to be safe" - more isn’t better

Also, never use ivermectin in pregnant animals without vet approval. While it’s generally considered safe in late-term pregnancy for horses and goats, it’s not risk-free.

When to Call the Vet

You don’t need to be a vet to use ivermectin safely - but you do need to know when to stop guessing.

Call your vet if:

• Your animal has never had ivermectin before
• You’re unsure of the correct dosage
• Your animal is a herding breed (Collie, Aussie, etc.)
• You’re treating a pregnant or very young animal
• Your pet shows any unusual behavior after dosing

Most vets will give you a pre-measured dose or write a prescription for a safe, vet-approved product. It’s worth the small cost. A single mistake can cost you your pet.

Alternatives to Ivermectin

There are other options, especially for animals sensitive to ivermectin:

• Moxidectin: Similar to ivermectin but less likely to cross the blood-brain barrier. Safer for MDR1-positive dogs. Used in ProHeart injections for heartworm prevention.
• Revolution (selamectin): Topical for cats and dogs. Treats fleas, ear mites, and some worms. No risk of overdose from licking.
• Drontal, Panacur (fenbendazole): Oral dewormers for intestinal parasites. Often used in goats and sheep as a rotation partner.
• Permethrin sprays: For external parasites like lice in poultry and livestock. Not for cats - they’re highly toxic to felines.

The best approach? Work with your vet to build a parasite control plan tailored to your animal’s species, age, environment, and risk level.

Final Thoughts

Ivermectin isn’t magic. It’s a tool. A powerful one - but only when used with care, knowledge, and respect. It’s saved millions of animals from debilitating parasites. But it’s also killed thousands because people assumed it was harmless.

If you’re using ivermectin on your animals, make sure you know the exact species, weight, and formulation. Keep records. Store it properly. Watch for reactions. And when in doubt - ask your vet. There’s no shame in getting help. Your animal’s life depends on it.