Antibiotics or antimicrobial drugs are effective medications for the treatment of bacterial infections in horses.

Common equine infections requiring antibiotics include infected skin wounds and abscesses, pneumonia, infectious diarrhea, cellulitis, peritonitis and more.

Many antibiotics have broad-spectrum action meaning they act against many different bacteria. Others more specifically target certain bacterial strains. Your veterinarian can determine which antibiotic is appropriate for your horse given their medical situation.

These drugs are not without risks, and they can have adverse effects on horse health when given without veterinary oversight.

Misuse and overuse of antimicrobials are common problems in the equine industry. This has contributed to growing antibiotic resistance whereby bacteria undergo changes that make them impervious to existing antibiotics.

As a horse owner, it is important to understand how antibiotics work, when they should be used and how to properly administer them to your horse.

This article will review antibiotic use in horses, types of equine antibiotics, and how to limit the associated risks for your horse.

Antibiotics for Horses

If you’re a long-time horse owner, chances are you have given your horse some form of equine antibiotic before. You may even have a leftover bottle of oral antibiotics in your feed room.

But reaching for antibiotics every time your horse scrapes his leg can have unintended consequences. These medications must be used carefully to maximize their benefits and minimize risks.

Antibiotic drugs treat bacterial infections in animals by killing bacteria or preventing them from multiplying so the horse’s immune response can beat the infection. [1][14]

Infections occur when harmful microorganisms invade and reproduce in your horse’s body. While beneficial probiotic bacteria help your horse stay healthy, exposure to pathogenic bacteria can lead to disease. [1]

Antibiotics combat pathogenic bacteria, but they can also disrupt the good microorganisms that are a part of the horse’s natural microbiome, potentially causing diarrhea or gut issues. This is one risk of antibiotic use in horses. [12]

How Antibiotics Work in Horses

Your horse is exposed to a wide variety of microorganisms in its environment. Most environmental bacteria are harmless, but some are disease-causing pathogens. [13]

Your horse has several natural defenses against pathogenic bacteria, including the good bacteria that populate the gastrointestinal tract. Skin also acts as a structural defense and the immune system fights against bacteria that enter the body. [2]

While the immune system can neutralize many bacterial infections in a healthy horse, severe infections may require medical intervention with antibiotics. [14]

Mechanisms of Action

In general, antibiotics work by disrupting biological processes in bacteria to impair their ability to function and replicate.

Antibiotics are able to selectively target bacteria and not animal cells because bacteria have different cell structures and metabolic functions. Antimicrobial medications have fatal consequences for microbes without damaging surrounding tissue. [15]

Some antibiotics work by deforming the bacterial cell wall, interfering with metabolic processes, targeting DNA function, or preventing energy production. [3]

Different antibiotics have different mechanisms of action targeting classes of bacteria responsible for the infection. Strategic selection is vital as not all antibiotics are equally effective. [3]

Treating Horses with Antibiotics

Several forms of antibiotics are administered to horses by veterinarians. [1] Systemic antibiotic treatments circulate throughout the entire body while local antibiotics only affect the area in which they are applied.

Systemic therapy is often necessary for infectious diseases but has a greater risk of disrupting the gut microbiome. [17]

This type of antibiotic includes oral and injectable medications. Oral antibiotics are simple for horse owners to administer, but veterinarians prefer intravenous antibiotics for immediate delivery in cases of severe infection. [1]

Horse owners are likely familiar with topical antibiotics, such as triple antibiotic ointment. Topical administration delivers antibiotic medicine directly to the affected tissues, most commonly the skin. [18]

Veterinarians can also use intra-articular administration of local antibiotics to treat affected joints. [19]

When to Use Antibiotics for Horses

Veterinary use of antibiotics in horses and other animals spans nearly a century. These medications have changed history: many once-fatal diseases are now treatable thanks to antibiotics. [20]

There are many cases when your veterinarian might recommend antibiotic treatment, but horse owners are often prone to overusing and misusing these drugs.

Successful antibiotic treatment depends on correct drug selection, dosing, time course and administration. [1] It is always recommended to consult a veterinarian before giving your horse any medicine.

The Equine Veterinarian’s Role

Depending on the situation, your vet may be able to use cultures to identify pathogenic bacteria and determine which antibiotics will work best. Alternatively, when time is of the essence, they can make educated recommendations based on your horse’s clinical signs. [6]

Most importantly, veterinarians can determine if your horse needs antibiotics in the first place or if these medications might not be necessary.

Sometimes, antibiotics cause more harm than good. The antimicrobial drug that worked for your horse last time may not be the best choice for his current infection. [17]

Veterinarians prescribe antibiotics for precise lengths of time and according to specific schedules. Not following instructions can interfere with therapeutic efficacy. [14]

Even if your horse’s condition improves within a few days of treatment, completing the entire treatment course is vital to prevent antibiotic resistance. [5]

Always follow manufacturer instructions regarding how and when to administer the drug. If your vet recommends dosing twice a day, try to administer the antibiotics 12 hours apart to ensure the drug reaches therapeutic levels in your horse’s body. [1]

Equine Infectious Diseases

Horses with a weakened immune system due to age, stress, chronic disease, immunosuppressive medications, or malnutrition are most susceptible to infectious diseases. But even healthy horses can get sick unexpectedly. [14]

Signs of internal illness include reduced appetite, diarrhea, lethargy, weight loss, poor coat quality, abnormal vital signs, fever, and unusual behaviors. [6]

Horse owners often sense when something is off with their horse and subtle changes can provide early clues about health concerns. If you suspect your horse is unwell, contact your veterinarian immediately.

Early diagnosis can help avoid unnecessary antibiotic use. Bacterial infections that don’t improve after three days may require antibiotics to resolve. [6]

Bacterial Infections

Examples of bacterial infections in horses include tetanus, strangles, Potomac horse fever, botulism, anthrax, lymphangitis, and cellulitis.

Viral Infections

Many equine infectious diseases involve viral infections, which don’t respond to antibiotics. Adult horses with a cough or nasal discharge often have viral infections. [6]

Vaccines are also available to protect against some of these viral conditions. [14]

Infected Wounds

Infection is often the main concern for equine wound care. A compromised skin barrier allows pathogenic bacteria from the environment to invade your horse’s body. [14]

Severe cuts, scrapes, gashes, and puncture wounds have a significant risk of infection. [21]

These injuries require veterinary evaluation to determine the appropriate treatment. If your veterinarian believes an infection is likely, they may prescribe antibiotics.

Lacerations near joints are particularly concerning, as joint infections can be life-threatening to horses and require aggressive early treatment. Treat any sign of an infected joint as an emergency. [19]

However, minor wounds often heal on their own without complications. Owners can help reduce the risk of infection by keeping the area clean of debris, allowing drainage, and applying local antiseptic. [7]

Signs of Infection

Signs of infection include heat, swelling, abnormal odor, red skin, yellow discharge, and tenderness. Talk to your veterinarian if your horse has a minor wound with signs of infection. [21]

Infected leg wounds can cause cellulitis, a bacterial infection of the soft connective tissues. This condition involves a sudden onset of extreme swelling that makes the limb look like a stovepipe. [8]

Chronic cases of cellulitis can lead to lymphangitis, so prompt treatment is critical. [8]

When Antibiotics Aren’t Necessary

While antibiotics are effective for some bacterial infections, these medications don’t always improve recovery times.

For example, abscesses caused by strangles might be part of an effective immune response to the disease. [22]

Hoof abscesses also rarely need antibiotics. Many abscesses improve with drainage, bandaging, and appropriate management. [9]

Many cases of fever involving minor respiratory symptoms are viral infections that should resolve independently. [6] Most superficial skin wounds heal without antibiotics when kept clean.

Common Antibiotics for Horses

Veterinarians will use clinical history and laboratory results to choose the best antibiotic for your horse.

There are fewer safe and effective classes of antibiotics for horses compared to other species. The limited options makes proper antibiotic selection critical for treating horses and preventing antibiotic resistance. [25]

You should never give your horse an antibiotic prescribed for your other pets without veterinary approval. [1]

Here are several of the most common antibiotics used for horses.


Sulfonamides are broad-spectrum antibiotics that stop various bacteria from multiplying by interfering with DNA