Intestinal Bacterial Infections in Horses

Intestinal Bacterial Infections in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

Most common symptoms

Bleeding / Diarrhea / Flatulence / Increased Heart Rate / Premature Labor / Wound


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Most common symptoms

Bleeding / Diarrhea / Flatulence / Increased Heart Rate / Premature Labor / Wound

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Intestinal Bacterial Infections in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

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What are Intestinal Bacterial Infections?

There are multiple types of intestinal bacterial infections that horses can experience. Two types are salmonella and Potomac horse fever. The infectious cause of diarrhea most diagnosed in horses is salmonella, which is the result of an infection of the horse’s intestinal tract by the bacterial pathogen salmonella. Potomac horse fever (PHF), also called monocytic ehrlichiosis and equine ehrlichial colitis, is another significant intestinal bacterial infection that can be experienced. This condition is most seen in the eastern United States, though it can occur throughout the country and can be mild through life threatening.

The bacteria responsible for intestinal bacterial infections in horses vary and infection can lead to diarrhea as well as a myriad of other symptoms. 

Symptoms of Intestinal Bacterial Infections in Horses

In the mild form of salmonella, as well as in the early stages of infection, your horse may have little or no diarrhea but suffer from a fever as well as mild stomach discomfort. In cases of greater severity, your horse will have diarrhea that is watery, copious and foul. Your horse will appear very uncomfortable and you may also notice the following:

  • Twitching of his tail
  • Straining
  • Periodic rectal prolapse
  • Dehydration
  • Discoloration of gums
  • Depression
  • Lack of appetite
  • Your horse repeatedly getting up and then lying back down as he tries to find a comfortable position

In the most severe cases of salmonella, which will cause significant damage to the large and small intestine of your horse, you may notice the following:

  • Bloating
  • Stomach discomfort
  • Flatulence
  • Bloody diarrhea

Should your horse be experiencing PHF, in most cases he will experience an initial fever that you might not notice. A second increase in fever can occur and likely include additional symptoms, like depression and a minimal appetite. In horses with this condition, 80% will experience diarrhea. Other possible symptoms include:

  • Laminitis (which will lead to him not being interested in moving)
  • Swelling in the limbs
  • Signs of toxins being present in his blood (increased heart rate, dark mucous membranes, sweating and stomach discomfort).



There are multiple types of intestinal bacterial infections. There are over 100 strains of salmonella. Most horses have at least one species of salmonella residing in their intestinal system and as regular residents, the salmonella bacteria help with the horse’s digestion.

Causes of Intestinal Bacterial Infections in Horses

Salmonella is the result of the bacterial pathogen salmonella. Symptoms that are seen in your horse result from the toxins that are produced by the bacteria. The source of the infection on a farm is often rodents. Many horses, however are carriers. In adults with salmonella, the majority of cases occur after the horse has experienced stress, perhaps in surgery or transport. Mares may shed the bacteria and infect a newborn foal.

PHF is caused by Neorickettsia risticii, which has previously been known as Ehrlichia risticii. In order for the disease to spread, an insect is needed. The insect can spread the disease from its source (like flukes or small flatworms) to the horse. The disease cannot be spread from horse to horse, meaning that quarantine is not required of an infected horse.

Diagnosis of Intestinal Bacterial Infections in Horses

In cases of an intestinal bacterial infection in your horse, your veterinarian will conduct a physical examination and ask you about symptoms you have noticed in your horse and for how long they have been present. 

When diagnosing salmonella, your veterinarian will consider the clinical signs as well as look to isolate the bacteria from your horse’s feces, blood or tissue. A fecal sample is more useful in identifying the bacteria than fecal swabs. Salmonella is not able to be consistently cultured from the feces of a horse, requiring your veterinarian to take several samples daily. Rectal biopsies are another way to confirm the presence of the organism, as well as a PCR (polymerase chain reaction) test.

A diagnosis of PHF is able to be confirmed through viewing the organism in either a blood or manure sample from the horse through a PCR test. Another way to confirm the diagnosis is through seeing a large increase in antibody levels in the bloodstream of your horse (taken 10 days apart).


Treatment of Intestinal Bacterial Infections in Horses

Should a diagnosis of infection by salmonella be confirmed, multiple treatment options are available. Depending on severity, your veterinarian may recommend no treatment at all, through your horse receiving intensive care at a hospital. Intravenous fluids may be utilized to help with shock and to rehydrate your horse, and antibiotics may be recommended to help your horse while his immune system responds to the infection. Other options to be considered are non-steroidal anti-inflammatory drugs like banamine (decreases shock) and plasma, which will provide your horse with protein and help to replace fluid loss and restore electrolyte balance. 

Should your horse be diagnosed with PHF, your veterinarian will consider treatment with the antibiotic oxytetracycline, which will typically lead to your horse’s symptoms improving within one day. This is the best treatment should the diagnosis be confirmed. If the veterinarian is not positive about the diagnosis, it is not a good choice for extended use due to the fact that oxytetracycline is eliminated through the liver and into the digestive tract of your horse. This could lead to the normal bacterial flora being adversely impacted, eliminating the helpful bacteria while leaving the bad.

Recovery of Intestinal Bacterial Infections in Horses

In horses experiencing salmonella, the illness runs its course within five to seven days, after which the horse will make a slow recovery. It may take a few weeks for his fecal consistency to normalize. You can assist your horse by providing electrolytes and fluids to help him avoid becoming dehydrated. Your veterinarian may recommend a follow up appointment to ensure that your horse is recovering well.

In PHF, the course of the disease is five to ten days. You will want to work with your veterinarian on providing supportive care whether or not antibiotics are administered. As with salmonella, follow up with your veterinarian may be recommended

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Intestinal Bacterial Infections Average Cost

From 220 quotes ranging from $1,000 - $6,000

Average Cost


Intestinal Bacterial Infections Questions and Advice from Veterinary Professionals

Intestinal Bacterial Infections Average Cost

From 220 quotes ranging from $1,000 - $6,000

Average Cost