What Ivermectin Is and What It Covers
Ivermectin is a broad-spectrum antiparasitic of the avermectin family, originally derived from a soil microorganism. In pigs it is used against gastrointestinal nematodes, lungworms and ectoparasites such as mange mites and lice. It is not effective against tapeworms or liver flukes, which require a different class of product.
Because it controls several parasite groups in one treatment, ivermectin has become a standard component of herd health programmes, but that convenience also makes overuse a real risk.
How Ivermectin Works in Pigs
Ivermectin acts on the nervous system of parasites by interfering with the ion channels that carry nerve signals. Affected parasites become paralysed and die, while the host is largely unaffected at therapeutic doses because the drug does not readily cross the blood-brain barrier at label rates.
After administration the drug is distributed through body tissues and reaches the digestive tract, the lungs and the skin, so a single treatment can address parasites in several sites. Its persistence in tissue is also the reason a withdrawal period is defined before slaughter.
Calculating the Correct Dose
The standard dose rate for pigs is 0.2 to 0.3 mg of ivermectin per kilogram of body weight. Every calculation depends on an accurate weight, because dosing by estimate is the most common cause of treatment failure and of overdose.
| Body weight | Dose at 0.2 mg/kg | Dose at 0.3 mg/kg | Practical note |
|---|---|---|---|
| 20 kg | 4.0 mg | 6.0 mg | Weigh each pig, never estimate |
| 40 kg | 8.0 mg | 12.0 mg | Reweigh growing pigs before every round |
| 60 kg | 12.0 mg | 18.0 mg | Confirm the tablet strength on the label |
| 80 kg | 16.0 mg | 24.0 mg | Split scored tablets accurately |
| 100 kg | 20.0 mg | 30.0 mg | Check the product is registered for swine |
Growing pigs should be re-weighed before each treatment cycle so that the dose follows the animal rather than an outdated figure recorded at entry.
Precautions and Contraindications
Overdose can produce neurological signs such as tremors, incoordination and lethargy; stop treatment and obtain veterinary advice immediately
The product is not recommended for pregnant sows, especially in early gestation
It does not act against tapeworms or liver flukes, so the diagnosis must be confirmed before treating
Serious parasitic infections should be managed under veterinary supervision
The withdrawal period stated on the label and required by local regulations must be observed before slaughter
Resistance Management and Record Keeping
Repeated use of a single drug class selects for resistant parasites, and resistance in swine nematodes is a recognised management concern. Deworm only when a parasite problem is confirmed or strongly suspected, and rotate between drug classes under veterinary advice rather than treating on a fixed calendar.
Keep records for every group: the date, measured body weight, dose given, product batch number and the interval between treatments. These records support treatment decisions, protect the food chain and provide the evidence needed if a withdrawal period is ever questioned. Good husbandry, clean pens and pasture rotation reduce parasite pressure, which in turn reduces the amount of drug required.
Frequently Asked Questions
Q: How much ivermectin should a pig receive?
The usual rate is 0.2 to 0.3 mg per kilogram of body weight, calculated from a measured weight rather than an estimate.
Q: Is ivermectin safe for pregnant sows?
It is generally not recommended for pregnant sows, particularly in early pregnancy, so veterinary advice should be obtained first.
Q: Does ivermectin kill tapeworms or liver flukes?
No. Those parasites require a different antiparasitic product, and the diagnosis should be confirmed before any treatment.
Q: What happens if a pig receives too much?
Excessive doses can cause tremors, incoordination and lethargy; treatment should be stopped and a veterinarian consulted without delay.
Q: Can the same product be used in other animals?
Ivermectin is used across several species, but formulations, doses and safety profiles differ, so only products approved for the target species should be used.
Q: What withdrawal period applies before slaughter?
It depends on the formulation and local rules; the period stated on the product label and confirmed by local regulations must always be followed.