Helpful vs Harmful: Antibiotic Risks in Horses
The discovery of antibiotics was one of the most important medical advances in history, and these drugs have had an immense impact on human and animal health. While antibiotics have saved countless lives, their use can also be associated with some very serious side effects and complications. For example, in horses, antibiotic-associated diarrhea (colitis) is a major issue.
By the nature of their intestinal tract, horses at among the highest risk species for developing serious diarrhea associated with antibiotic use. The intestinal tract of a horse is full of billions of bacteria of different types. These bacteria are important for normal digestion, and also help to prevent infection by "bad" bacteria such as Salmonella and Clostridium difficile. Antibiotics can disrupt the balance of this complex bacterial population. The imbalance itself can cause problems, and can also make it easier for bad bacteria to move in, grow and cause disease.
Here are some important points to remember about antibiotics, particularly in horses:
- Antibiotics can only kill bacteria. They should not be used when a bacterial infection is not present and not likely to occur. Antibiotics are too commonly misused for viral infections in horses, which puts the animals at unnecessary risk.
- Any antibiotic can cause diarrhea, but some drugs are considered higher risk. Erythromycin and tetracyclines are considered high-risk in most areas of North America. Certain drugs, such as lincomycin and oral penicillins, are such high risk that they should never be used in adult horses.
- Both oral and injectable antibiotics can also cause diarrhea. Drugs that are injected can still reach the intestinal tract and affect the bacteria there. Some drugs, like tetracycline, are actively pumped into the intestinal tract from the bloodstream, resulting in relatively high concentrations in the intestine, even if the drug was given by injection.
- While some antibiotics can be purchased over the counter in some areas, antibiotics should never be given without the direct recommendation of a veterinarian.
- If your horse is being treated with antibiotics and develops diarrhea, contact your veterinarian immediately.
- There is no known way to reduce the risk of antibiotic-associated diarrhea in horses, other than to avoid unecessary use of antibiotics. Some people treat horses with probiotics or yogurt, but currently there is no evidence that this is beneficial (but it probably doesn't hurt, at least in adult horses).
Another major concern with antibiotic use is the development of antibiotic resistance in bacteria, but that's a topic for another post (or two, or three or more!).
More information about Clostridium difficile and probiotics in horses can be found on the equIDblog Resources page.
