Bad Horse Bugs

Horse owners and vets must use antimicrobials responsibly to help reduce bacterial drug resstance.
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Antimicrobial resistance and the looming problems with MRSA infections.

MRSA. Salmonella. Enterococcus. If these bacteria ring a bell, here’s why: They are just a few of the countless bad bugs that can infect horses and humans or are becoming resistant to the antibiotics we use to treat them. Elizabeth Santschi, DVM, Dipl. ACVS, a clinical associate professor at the Ohio State University, says horse owners must use antimicrobials responsibly to help reduce development of bacterial resistance against these drugs.

"This responsibility involves not just the choice of drugs, but also duration and concentration of a drug," she explains. "Antibiotics should be used at sufficient concentration for the appropriate amount of time to do the job. Where we get into trouble is when we use improper dose (generally too low) or use the drug for too short (of a) duration." If the antibiotic therapy has not eliminated the bacterial infection completely by the time you stop using the drug, the remaining bacteria are the most hardy–and this can lead to development of antibiotic resistance among these bugs.

"We’re also handicapped in equine medicine and surgery because we have a limited number of antibiotics in our selection that are safe to use in horses and also economical," Santschi continues. "Some (effective) antibiotics are prohibitively expensive for a 1,000-pound horse; they would cost hundreds or thousands of dollars a day."

Amy Johnson, DVM, Dipl. ACVIM, a lecturer in clinical studies at the University of Pennsylvania, says that some drugs also require intravenous (IV) administration that might necessitate a hospital or layup facility visit, as opposed to availability as a pill the owner can give to the animal at home. This increases total treatment cost. And the longer the horse is hospitalized, the greater his chance of developing complications due to pathogen exposure, because the most resistant forms of microbes (such as Enterobacter, Enterococcus, and MRSA–methicillin-resistant Staphylococcus aureus), are often present in clinics. For instance, "MRSA infections are generally due to catheter site infections or surgical site infections," says Johnson

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Written by:

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey’s Guide to Raising Horses and Storey’s Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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