Florfenicol 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.

Florfenicol is a prescription antibiotic in the phenicol family. In cattle, it is most often sold as NUFLOR or as a generic injectable product. It works by blocking bacterial protein synthesis, which helps stop susceptible bacteria from multiplying. In practice, your vet may choose it when they need a broad-spectrum antibiotic for common bacterial respiratory or soft tissue infections.

In the United States, florfenicol is labeled for cattle only in specific classes and situations. It is commonly used in beef cattle and certain non-lactating dairy cattle, but label restrictions matter. It is not approved for use in female dairy cattle 20 months of age or older, and it should not be used in veal calves, calves under 1 month of age, or calves on an all-milk diet because withdrawal and residue safety are not established for those groups.

Because cattle are food-producing animals, florfenicol use has to balance treatment needs with meat and milk residue rules. That means your vet will consider the animal's age, production class, route of injection, and the exact product label before recommending it. For pet parents caring for a family cow or small herd animal, that food-safety piece is a major reason not to dose this drug without direct veterinary guidance.

Florfenicol is best known for treating bovine respiratory disease (BRD) caused by susceptible bacteria such as Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni. These infections can cause fever, cough, nasal discharge, fast breathing, depression, and reduced appetite. In some groups of newly arrived or stressed cattle, labeled florfenicol products may also be used for control of BRD in animals considered high risk before obvious illness spreads through the group.

It is also labeled for bovine interdigital phlegmon, often called foot rot, when susceptible bacteria are involved. In that setting, your vet may consider florfenicol if a cow has sudden lameness, swelling between the claws, pain, and a foul odor from the foot.

Florfenicol does not treat viral disease, parasites, or every cause of fever and lameness. That is why an exam matters. Your vet may recommend florfenicol when the history, physical exam, herd risk, and likely bacteria fit the label and the animal's production status.

Florfenicol dosing in cattle depends on the route and the reason it is being used. Common labeled injectable regimens are 20 mg/kg intramuscularly, then repeated in 48 hours, or 40 mg/kg subcutaneously once. On many labels, that corresponds to 3 mL per 100 lb IM, followed by a second dose 48 hours later, or 6 mL per 100 lb SC once. Injections are typically given in the neck only, and no more than 10 mL per injection site should be used.

Your vet will choose the route based on the diagnosis, handling practicalities, tissue reaction concerns, and slaughter timing. The subcutaneous one-time dose is often convenient when minimizing repeat handling matters. The two-dose intramuscular protocol may be selected in other situations. For cattle at high risk of developing BRD, labeled products commonly use the single 40 mg/kg SC dose.

Withdrawal times are critical. For NUFLOR Injectable Solution, cattle treated by the subcutaneous route must not be slaughtered within 38 days, and intramuscular injection can cause local tissue reactions that persist beyond 28 days. Different florfenicol-containing products can have different withdrawal periods, so your vet should confirm the exact label being used. Never estimate the dose by eye or substitute one product's withdrawal time for another.

Many cattle tolerate florfenicol well when it is used exactly as labeled, but side effects can happen. The most common practical concern is injection-site reaction, especially with intramuscular use. Swelling, soreness, and tissue changes can persist for weeks, which is one reason neck-only injection technique matters.

Some cattle may show a temporary drop in feed intake after treatment. In safety studies and label summaries, higher or repeated doses were associated with reduced appetite, decreased water intake, soft stool or diarrhea, mild depression, dehydration, weight loss, and increased serum enzymes. These effects were more noticeable at multiples of the labeled dose and generally resolved after treatment stopped.

Call your vet promptly if your cow seems weaker than expected, stops eating, becomes dehydrated, develops marked swelling at the injection site, or does not improve within the timeframe your vet discussed. If breathing effort worsens, fever persists, or the animal becomes unable to rise, that is more urgent and needs veterinary reassessment right away.

Florfenicol is a protein-synthesis inhibitor and is generally considered bacteriostatic at typical concentrations, although it can be bactericidal against some organisms. Because of that, your vet will think carefully before combining it with other antibiotics. In some cases, pairing a bacteriostatic drug with a bactericidal drug may be less useful than choosing one well-matched treatment plan based on the likely bacteria and the animal's condition.

There are no widely used day-to-day interaction lists for cattle pet parents to manage on their own, but the important point is this: tell your vet about every product the cow has received, including antibiotics, anti-inflammatories, medicated feed, supplements, and any recent injections. That helps your vet avoid overlapping therapies, residue problems, and unnecessary antimicrobial use.

For food animals, the biggest practical "interaction" issue is often with withdrawal planning rather than a classic drug-drug reaction. Extra-label use can greatly extend withdrawal intervals, especially in animals connected to milk production. Your vet may consult residue resources such as FARAD when a case falls outside standard label use.