As we know, bacteria are one of the most ubiquitous life forms on the planet. While most bacteria don’t have much of an impact on higher life forms (such as humans and horses), there are some that can cause disease. Horses are exposed to a myriad of bacteria daily; most of the time, their immune systems are able to fight off bacterial incursions without developing clinical disease. Bacterial disease occurs when a horse’s immune system is unable to mount a sufficient defense and the bacteria is able to spread throughout the horse’s body.

When a horse breaks with bacterial disease, in most cases, the source of bacteria is likely to have been contaminated water, food or feces.¹ Like humans, horses can become infected with bacterial diseases after their immune system has already been compromised by another illness, such as a virus. Bacterial infections tend to be more common in horses that are stressed by travel or spend a lot of time training or in stables frequented by other horses. Foals and geriatric horses are at higher risk of becoming sick, because their immune systems are not as strong as adult horses.

Common Bacterial Diseases of Horses

Common bacterial diseases that occur in the horse include:

• Salmonella
• E Coli
• Strangles
• Potomac Horse Fever
• Pneumonia

Many of the bacterial infections occurring in horses are diseases of the gastrointestinal tract. There are numerous types of intestinal bacterial infections that horses can experience, with two of these being salmonella and Potomac horse fever. The infectious cause of diarrhea most diagnosed in horses is salmonella.¹

There are actually over 100 strains of salmonella,² and most horses have at least one strain in their intestinal system. The bacteria help with the horse’s digestion, but under stress, these can proliferate and cause disease. In mild cases of salmonella and in the early stages of the disease, a horse may have little or no diarrhea, but may suffer from a fever.

In more severe cases, a horse can have diarrhea that is watery, copious and foul-smelling. The horse will appear very uncomfortable and may display:

• Tail twitching
• Straining
• Periodic rectal prolapse
• Dehydration
• Gum discoloration
• Depression
• Lack of appetite

In very severe cases of salmonella (which can cause significant damage to the large and small intestine), the horse may display:

• Bloating
• Flatulence
• Bloody diarrhea

Potomac horse fever (PHF, also called monocytic ehrlichiosis and equine ehrlichial colitis), is another intestinal bacterial infection common to horses. Potomac horse fever is most frequently seen in the eastern U.S., although it can occur throughout North America.² The disease can be mild or life-threatening.

In horses experiencing Potomac horse fever, the horse will experience an initial fever that may go unnoticed. Higher fever typically develops with additional symptoms, such as depression and a lack of appetite. In horses with PHF, 80% experience diarrhea. Other symptoms can include:

• Swelling in the limbs
• Laminitis
• Signs of increased toxins in the blood (increased heart rate, dark mucous membranes, sweating)

Other bacterial pathogens attack the horse’s respiratory tract. Veterinarians are routinely called out to diagnose and treat horses with poor performance, exercise intolerance, coughing, and nasal discharge. The list of potential causes for these complaints can be quite long, but is often attributable to Strangles. This is a highly contagious disease of horses, donkeys and ponies that is caused by the bacteria Streptococcus equi. Its name is attributed to the strangled breathing sounds made by affected horses due to profuse nasal discharge and swellings that form in the head and neck region.¹

Strangles is highly contagious, and is spread via nasal secretions.^1,2 The bacteria can contaminate water or feed sources and is very easily transmitted orally as well as via the respiratory tract. Although this disease can be life-threatening, most horses fully recover from strangles in two to four weeks with proper treatment.

Doxycycline Treatment for Horses

Doxycycline is an oral and parenteral tetracycline antibiotic that is widely used in human and animal medicine. Thus, doxycycline generally has similar action to other tetracycline medications.

Where to buy Doxycycline

Doxycycline is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Panchaud Y, Gerber V, Rossano A, Perreten V. Bacterial infections in horses: a retrospective study at the University Equine Clinic of Bern. Schweiz Arch Tierheilkd. 2010 Apr;152(4):176-82. doi: 10.1024/0036-7281/a000040. PMID: 20361396.

²Samper, J. Disease Transmission in Horses. Theriogenology, Volume 66, Issue 3, August 2006, Pages 551-559.