Food Animal Drugs

Food Animal Antibiotics

Due to the restrictions on antimicrobial use, choosing antimicrobials for food and fiber animals is somewhat simpler than in dogs and cats.

Beginning in 2023, no more over the counter antimicrobials are allowed. This will affect injectable oxytetracycline, injectable tylosin, procaine penicillin G and mastitis tubes.

Currently, I most often use Naxcel (ceftiofur sodium) preoperatively for dairy cattle for Csections and for most abdominal surgeries.  Naxcel does not affect the milk supply and the cow’s milk can be sold. I use penicillin or ampicillin for rumenotomies due to the flora involved and ampicillin for most beef and small ruminant surgeries. Excede (ceftiofur acid) is also useful in beef animals. The longer acting formulations (procaine penicillin, ceftiofur acid) are handy for therapeutic use because they last longer in the cow; however, they also last longer in the milk, meaning the milk withholding (how long before it can be safely sold) is prolonged, as well. These are fine for beef cattle whose milk isn’t sold.

Fluroquinolones should not be used except as labeled.

Aminoglycosides such as gentamicin are not prohibited but have a tremendously long meat withdrawal; the drugs can be found in the kidneys for over 18 months. Just don’t use them in anything that could be eaten (cattle, sheep, goats, pigs, camelids).

While I tend to assume prophylactic antibiotics are important for my abdominal surgeries, recent research suggests that antibiotics are needed pre/postop for Csections but that antibiotics should not be used for elective abdominal surgery.

Primary considerations:

  • are you likely dealing with gram positive, gram negative or both types of organisms?
  • is there a drug labeled for the species and the disease?
  • what drugs are legal in the species?
  • where is the infection? can the antibiotics reach it? what drugs will be effective in that environment?
  • how sick is the animal? can you use a bacteriostatic drug or do you need a bacteriocidal drug?
  • does the animal have any other conditions that would increase the risk of certain drugs? e.g. renal disease or liver failure
  • what drugs should you avoid using in order to save them for human use?

Secondary considerations

  • is the animal milking or likely to go to market soon? what is your withholding window?
  • how valuable is the animal and how expensive is the drug?
  • what routes of administration are available to you and how frequently can the drug be administered?
  • what are the resistance patterns in your area? can you assume certain drugs will be more effective than others?

Selecting antimicrobials

by Dr. Alex Bianco


Drug IV IM/SQ PO Anaerobes Good penetration Use in a dairy cow
Penicillin x x x x
Ampicillin x x x
Cephalosporins EQ/SRC x x (on label only)
Fluoroquinolones EQ FA EQ
Macrolides FA FA/foals
Chloramphenical/Florfenicol FA EQ x x
Tetracyclines x FA x

Swine Antibiotherapy Handbook: (also has good info for other species)

Gamithromycin SQ (macrolide)is being studied for use in camelids.

Small ruminants (from Dr. Pippa Gibbons)

Antimicrobial group Drug examples Spectrum of activity Notes
Beta lactams- penicillins PPG, ampicillin Anaerobic, Gm +, some Gm – PPG is not effective at label doses
Beta lactams, cephalosporins Naxcel, Excenel, Excede Gm + and Gm –
Tetracyclines LA200 broad spectrum, rickettsials Oxytetracycline used at cattle dose
Florfenicol Nuflor, Resflor broad spectrum Florfenicol used at cattle dose
Macrolides Draxxin, Micotil, Zactran, Tylan Gm +, respiratory Gm – Gamithromycin, tylosin and tulathromycin used at cattle dose

Micotil kills goats, pigs, horses, humans and camelids; use 10mg/kg SQ for sheep

Sulfas Albon broad spectrum



Procaine Pencillin G is labeled for administration at a very low dose. This label dose is NOT effective and should be avoided. Generally doses of 22,000 – 66,000 IU/kg are recommended rather than the label dose of 6600 IU/kg.

This article does a great job of fairly painlessly explaining why and how pharmacodynamics and pharmacokinetics play a role.

Update on withdrawal intervals following extralabel use of procaine penicillin G in cattle and swine. JAVMA | JAN 1, 2022 | VOL 260 | NO. 1



Antimicrobial resistance learning site

Pharmacology chapter, Dairy Production Medicine ebook

Randomized prospective trials to study effects of reduced antibiotic usage in abdominal surgery in cows. J. Dairy Sci. 101:8217–8223. With careful attention, maybe we can pick which cases get preop antibiotics.

Food Animal Drug Regulations

OSU VMC Antimicrobial use guidelines – great place to start when choosing a drug



Wikipedia– often has very good pharmacological information

For Future Reference | Create a drug reference table

Pharmacology course notes and the online drug monographs


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Large Animal Surgery - Supplemental Notes Copyright © by Erin Malone, DVM, PhD is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.