Ivermectin for Cow: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Ivermectin is a macrocyclic lactone antiparasitic used in cattle to treat and control a range of internal and external parasites. In U.S. cattle practice, it is commonly available as an injectable product and as a pour-on topical product. Your vet may choose one form over another based on the parasite involved, the age and production class of the animal, and food-safety withdrawal requirements.

In cattle, ivermectin is used because it has activity against many important parasites, including gastrointestinal roundworms, lungworms, sucking lice, mange mites, and cattle grubs. Some labeled products also cover additional parasites depending on the exact formulation. It is not a one-size-fits-all dewormer, though. Parasite resistance, herd history, season, and local parasite pressure all matter.

Because cattle are food-producing animals, ivermectin use also involves meat and milk withdrawal rules. Those rules vary by product and route. For example, injectable ivermectin products commonly carry a 35-day slaughter withdrawal, while some pour-on products carry a 48-day slaughter withdrawal. Milk withdrawal has not been established for many ivermectin cattle products, so your vet should guide any use in dairy animals.

Ivermectin is most often used in cattle for parasite control, not for bacterial or viral disease. Labeled uses include treatment and control of gastrointestinal roundworms, including inhibited Ostertagia ostertagi in some products, lungworms such as Dictyocaulus viviparus, and several external parasites including sucking lice, mange mites, and cattle grubs.

Your vet may recommend ivermectin when cattle have signs that fit a parasite problem, such as poor weight gain, rough hair coat, coughing linked to lungworms, itching from lice or mange, or seasonal grub concerns. In herd medicine, it may also be part of a broader parasite-control plan that includes fecal testing, pasture management, and timing treatment to reduce resistance pressure.

Product choice matters. Injectable and pour-on ivermectin do not behave exactly the same in the body, and pour-on absorption can be more variable. In 2026, the FDA also issued an Emergency Use Authorization allowing Ivomec 1% Injection to be used in certain cattle situations for prevention of New World screwworm infestations associated with wounds, birth, or castration. That emergency authorization is separate from the product's routine labeled parasite uses.

Always use ivermectin exactly as your vet directs and exactly as the label allows for that product. In cattle, dosing depends on the formulation. A common labeled dose for 1% injectable ivermectin is 0.2 mg/kg subcutaneously once, which is often expressed as 1 mL per 110 lb body weight for a 10 mg/mL product. Merck also lists 0.2 mg/kg by mouth or subcutaneously, and 0.5 mg/kg as a pour-on, for certain cattle parasite uses.

Accurate body weight matters. Underdosing can lead to treatment failure and may encourage parasite resistance. Overdosing raises the risk of adverse effects and residue problems. Your vet may recommend a scale weight, weight tape, or a conservative estimate based on the heaviest animals in a treatment group.

Food-animal restrictions are a major part of dosing decisions. Injectable ivermectin products for cattle commonly have a 35-day slaughter withdrawal, while some pour-on products have a 48-day slaughter withdrawal. Many cattle ivermectin labels state that milk withdrawal has not been established and that the product should not be used in female dairy cattle of breeding age or in veal calves. If your vet uses a drug extra-label in a food animal, they must assign an appropriate withdrawal interval and treatment records should be kept carefully.

When used at labeled doses, ivermectin generally has a wide safety margin in cattle. Many animals show no obvious side effects. Mild issues can include temporary injection-site swelling, brief irritation after topical use, or stress related to handling and restraint.

More serious problems are uncommon but can happen, especially with dosing errors, product misuse, or extra-label use. Signs of toxicity may include depression, weakness, incoordination, stumbling, drooling, tremors, or other nervous system changes. Very high doses have been associated with more severe toxicity, and Merck notes that high doses of ivermectin can contribute to liver injury.

See your vet immediately if a cow becomes dull, wobbly, unable to rise, stops eating, or shows sudden neurologic signs after treatment. Also call your vet if there is a large injection-site reaction, if multiple animals fail to improve, or if you are worried about accidental use in the wrong class of cattle. In food animals, a dosing mistake is both a health issue and a residue issue, so prompt veterinary guidance matters.

Ivermectin belongs to the macrocyclic lactone family. In general, your vet will be cautious about combining it with other drugs in the same family, such as doramectin, eprinomectin, or moxidectin, unless there is a clear medical reason and a defined plan. Stacking similar parasite products can increase exposure without improving results.

Drug handling in the body can also be affected by formulation, route, body condition, and transport proteins such as P-glycoprotein. While this issue is discussed more often in dogs, Merck notes that altered P-glycoprotein function has also been reported in some cattle. That means unusual sensitivity is possible in rare cases.

The biggest practical interaction concern in cattle is often not a classic drug-drug interaction. It is the combination of the wrong product, the wrong route, and the wrong production class, which can create residue violations or safety problems. Tell your vet about every dewormer, fly-control product, injectable medication, and feed additive the animal has received recently so they can build a safe plan.