Enrofloxacin is a prescription antibiotic that cattle producers mainly reach for when calves come down with pneumonia, the costly respiratory disease that follows shipping and mixing. It was the first antibiotic of its family developed specifically for animals rather than people.1The Bovine Practitioner. Microbiology and Pharmacology of Enrofloxacin in Cattle Because that same drug family treats serious human infections, it is one of the most tightly restricted antibiotics a cattle producer can use. How you use it, and on which animals, is set by federal rules as much as by your vet’s judgment.
What Enrofloxacin Treats in Cattle
In the U.S., enrofloxacin is approved to treat bovine respiratory disease (BRD), the pneumonia often called shipping fever. It is also approved to control BRD in cattle at high risk of developing it, and to treat and control respiratory disease in pigs.2U.S. Food and Drug Administration. Extralabel Use and Antimicrobials A conditional approval covers clinical anaplasmosis in specific classes of cattle.3U.S. Food and Drug Administration. Extralabel Use and Antimicrobials It is not labelled for scours, foot rot, pinkeye or mastitis in cattle, and using it for those would be illegal off-label use.
A calf with BRD typically runs a fever, holds its ears low, and has nasal discharge, a cough and fast breathing. It often goes off feed. Early treatment matters, since damaged lungs can permanently slow a calf’s growth.
Treatment means giving the drug to an animal already showing illness. Control means giving it to a whole group expected to get sick, before signs appear. Your vet decides which applies.
Enrofloxacin works against a broad range of bacteria.4PubMed Central. Enrofloxacin—The Ruthless Killer of Eukaryotic Cells or the Last Hope in the Fight against Bacterial Infections? It jams the enzyme bacteria use to coil and reseal their DNA, so the DNA breaks apart and the cell dies rapidly.5The Bovine Practitioner. Microbiology and Pharmacology of Enrofloxacin in Cattle In the calf’s body, part of the drug is converted into ciprofloxacin, a related antibiotic that also kills bacteria,6PubMed. Pharmacokinetics of Enrofloxacin and Its Metabolite Ciprofloxacin in Nanyang Cattle so one injection delivers two active drugs.
How Enrofloxacin Is Given and Dosed
Enrofloxacin for cattle comes as an injectable solution, commonly 100 mg per mL, given under the skin. Labels offer a single high dose or a lower daily dose repeated over several days, calculated by body weight. Your vet and the label set the exact amount.
Because dosing goes by weight, guessing is risky. Eyeballed weights often lead to underdosing heavy calves, which can fail to clear the infection and encourages resistance. Use a scale or weight tape, and round up within the label’s range.
No more than 20 mL should go into a single injection site.7Virbac. Tenotrylâ„¢ (enrofloxacin) injectable solution Injections under the skin can cause a short-lived tissue reaction that may have to be trimmed off at slaughter.8Virbac. Tenotrylâ„¢ (enrofloxacin) injectable solution A large animal needing more than 20 mL gets split injections in separate spots. Give them in the neck, the standard beef quality location, to keep any damage out of valuable cuts.
Use a clean, sharp needle and change it often. Tent the loose skin of the neck and inject under it, not into muscle.
The drug reaches the lungs where it’s needed. After injection, levels in the fluid lining the lungs stay high enough to stop typical BRD bacteria 48 hours later.9PubMed Central. Comparison of Active Drug Concentrations in the Pulmonary Epithelial Lining Fluid and Interstitial Fluid of Calves Injected with Enrofloxacin, Florfenicol, Ceftiofur, or Tulathromycin
Single doses may also be gentler on gut bacteria. After a single dose in steers, gut E. coli briefly became less sensitive to the drug but returned to normal by 48 hours, while after repeated doses it stayed less sensitive through 48 hours.10PubMed Central. Dosing Regimen of Enrofloxacin Impacts Intestinal Pharmacokinetics and the Fecal Microbiota in Steers11PubMed Central. Dosing Regimen of Enrofloxacin Impacts Intestinal Pharmacokinetics and the Fecal Microbiota in Steers
If a calf doesn’t improve, recheck its temperature and appetite within the days your vet specifies. Don’t simply repeat enrofloxacin on your own; call the vet.
How Well It Works Against Other BRD Drugs
Results are mixed when enrofloxacin is given to a whole high-risk group on arrival. In one trial of high-risk calves, 33.7% given enrofloxacin later needed BRD treatment, versus 18.3% given tulathromycin.12PubMed Central. Comparative efficacy of enrofloxacin to that of tulathromycin for the control of bovine respiratory disease and prevalence of antimicrobial resistance in Mannheimia haemolytica in calves at high risk of developing bovine respiratory disease Death rates in that trial were similar, 12.2% versus 10.1%.13PubMed Central. Comparative efficacy of enrofloxacin to that of tulathromycin for the control of bovine respiratory disease and prevalence of antimicrobial resistance in Mannheimia haemolytica in calves at high risk of developing bovine respiratory disease A feedlot trial in Mexico found no difference in illness, deaths, weight gain or feed efficiency between the two drugs.14The Bovine Practitioner. An evaluation of arrival metaphylaxis with enrofloxacin compared to tulathromycin in feedlot cattle at high risk of developing bovine respiratory disease in Mexico
In sick dairy heifer calves, retreatment was somewhat more common. Among preweaned dairy heifers treated for respiratory disease, 27.6% given enrofloxacin needed retreatment within 7 to 10 days, versus 21.2% given tulathromycin.15PubMed. Comparative efficacy of enrofloxacin and tulathromycin for treatment of preweaning respiratory disease in dairy heifers More than one retreatment was needed in 9.3% versus 4.1%.16PubMed. Comparative efficacy of enrofloxacin and tulathromycin for treatment of preweaning respiratory disease in dairy heifers Growth rates did not differ between the groups.17PubMed. Comparative efficacy of enrofloxacin and tulathromycin for treatment of preweaning respiratory disease in dairy heifers
A retreatment rate is not the same as a treatment failure. It counts calves a caretaker judged still sick and treated again, so it partly reflects human decisions. A higher rate means extra labor, drug and withdrawal time, not clearly more lost calves.
Bacteria don’t all respond the same way. Some strains of the main pneumonia bacterium die off sharply as drug levels rise, while others respond only slightly.18PubMed Central. Variation in fluoroquinolone pharmacodynamic parameter values among isolates of two bacterial pathogens of bovine respiratory disease The same dose can work well in one herd and less well in another. Ask your vet which drug has worked best in local cattle.
A vet might still choose enrofloxacin because it acts fast and kills bacteria rather than just stopping their growth. It can be useful when other drugs have failed in an outbreak. Cost, withdrawal time and animal class also shape the choice.
Withdrawal Time and Which Cattle Can’t Receive It
The withdrawal period, the wait before a treated animal can enter the food supply, is 28 days from the last treatment.19Norbrook. Enroflox 100 Enrofloxacin Injection No withdrawal period has been set for calves that aren’t yet ruminating.20Journal of the American Association of Bovine Practitioners. Enroflox 100
The clock starts from the day of the last injection, so another round after a relapse restarts it and can push back a planned sale date. Write the clear date on the animal’s record when you treat.
Enrofloxacin is not approved for female dairy cattle 20 months of age or older, including dry cows.21agproud.com. Baytril 100 (enrofloxacin) Injectable approved by FDA for control of BRD in high-risk cattle Use in these cows may leave drug residues in milk or in calves born to them.22Norbrook. Enroflox 100 It must not be used in calves to be processed for veal.23PubMed Central. ENROFLOXACIN 100- enrofloxacin injection, solution Dairy heifers can receive it only while younger than 20 months.
A dry cow is still a dairy female and is excluded. Bred heifers approaching 20 months may cross the line before calving.
Tag or mark treated animals so they aren’t sold by mistake, and log the date, dose, product and clear date. Check the records before every sale or shipment.
Why Off-Label Use Is Illegal
Off-label use means using a drug in a way the label doesn’t specify: a different disease, dose, route, duration or animal class. In 1997 the FDA prohibited all off-label use of fluoroquinolones, enrofloxacin’s drug family, in food-producing animals.24U.S. Food and Drug Administration. Extralabel Use and Antimicrobials The reason is that off-label use could raise levels of drug-resistant germs in animals at slaughter that can infect people.25U.S. Food and Drug Administration. Extralabel Use and Antimicrobials Unlike most antibiotics, even a vet can’t legally prescribe it off-label for cattle.
A vet who says no to a request, such as a longer course for a stubborn case, is following the law. If a calf needs something the label does not allow, the lawful route is a different, approved drug.
The measured risk to people from approved use is very small. One estimate for labelled use in dairy heifers put the added risk of a hard-to-treat human Campylobacter case at about one case every 13 years across all U.S. adults.26PubMed. Quantitative risk from fluoroquinolone-resistant Salmonella and Campylobacter due to treatment of dairy heifers with enrofloxacin for bovine respiratory disease For Salmonella the estimate was about one case every 293 years.27PubMed. Quantitative risk from fluoroquinolone-resistant Salmonella and Campylobacter due to treatment of dairy heifers with enrofloxacin for bovine respiratory disease
Resistance and Testing Before Treatment
Across U.S. and Canadian BRD bacteria from 2000 to 2009, typical strains stayed just as easy to kill, but the most resistant tenth became at least 16 times harder to kill.28PubMed. A ten-year (2000-2009) study of antimicrobial susceptibility of bacteria that cause bovine respiratory disease complex–Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni–in the United States and Canada
Your vet can culture samples from sick calves and test which drugs still work. A culture grows the bacteria and exposes them to a set of drugs, then reports whether each is likely to work against that strain. The result describes the bacteria in that sample, so it is a strong guide for the sick calf and a reasonable one for herdmates in the same outbreak. Results take days, so treatment usually starts before the report arrives and is adjusted if it shows a problem.
Tests can disagree. Results for enrofloxacin varied depending on whether samples came from the nose, throat or deep lungs.29PubMed. Agreement of antimicrobial susceptibility testing of Pasteurella multocida and Mannheimia haemolytica isolates from preweaned dairy calves with bovine respiratory disease Deeper samples taken by a vet may give a more reliable answer than a nasal swab. Gene tests can also miss resistance that shows up in lab growth tests.30PubMed Central. Comparison of virulence and resistance genes in Mannheimia haemolytica and Pasteurella multocida from dairy cattle with and without bovine respiratory disease
Ask for testing when several calves fail treatment in the same group, or when death losses climb despite treatment. Testing the lungs of dead animals can guide treatment for the rest of the pen.
A few habits slow resistance: use full label doses, never partial ones, and reserve the drug for cases your vet selects. Better arrival management, vaccination and ventilation also mean fewer antibiotics are needed.
Safety, Manure, and Handling
Enrofloxacin can leave high residue levels in cattle manure.31PubMed. Residual enrofloxacin in cattle manure increased persistence and dissemination risk of antibiotic resistance genes during anaerobic digestion It holds up better than many antibiotics in manure digesters and can help resistance genes persist.32PubMed. Residual enrofloxacin in cattle manure increased persistence and dissemination risk of antibiotic resistance genes during anaerobic digestion Manure-amended topsoil holds onto it, but heavy rain can wash it deeper, especially in light soils.33Journal of Environmental Chemical Engineering. Enhanced adsorption and leaching behavior of fluoroquinolone antibiotics in soil amended with cattle manure under varying rainfall condition Avoid spreading manure from recently treated animals right before heavy rain or near wells and streams.
Keeping treated animals’ pens separate, where practical, makes it simpler to manage that manure on its own. Don’t spread it onto saturated or frozen ground.
Wear gloves when handling the product; people sensitive to quinolone antibiotics should avoid contact. Store it per the label, away from light and children. Dispose of needles in sharps containers and empty bottles as the label directs, and watch the injection site for swelling over the next days.