Diarrheal Disease (Bacterial) in Horses

As there are numerous factors that may lead to frequent, watery diarrhea, diagnostic testing may be required to identify the cause. Your veterinarian will need to be contacted to provide care for your horse.

Diarrheal disease in horses caused by bacterial colitis is often due to the overgrowth of naturally occurring bacteria in the gut, or due to the introduction of an infectious agent. This can be caused by infection following exposure to contaminated water, or by compromised gut flora due to illness or antibiotic use.

The most obvious symptom of diarrheal disorder in horses is excessive watery diarrhea. Other symptoms that you may observe are:

• Depression and reduced appetite 
• Fever 
• Increased heart rate 
• Dehydration ( increased skin tenting, sunken eyes, reduced perspiration)
• Red gums and a purple line on the gum around the incisors (caused by endotoxemia, the build up of the toxin lipopolysaccharide (LPS) in the blood due to the breakdown of excessive levels of gram negative bacteria)

Diarrhea is seen when an excess of water is present in the manure, this can be caused by a range of conditions. This can cause a rapid loss of fluid, leading to dehydration, low blood pressure and reduced blood flow to vital organs which can result in shock. 

This can be caused following a disruption to the normal microbial flora of the gut. This can be when an overgrowth of naturally occurring bacteria in the gut occurs, or following the introduction of a new bacteria. This is often caused by bacteria of the Salmonella and Clostridial organisms. Horses may be exposed to these organisms via contaminated drinking water or waterways, through contact with horses who are shedding the disease, or through contaminated feed.

Causative organisms include: 

• Salmonella spp
• Clostridium – there are three types of this bacterium, type A, B and C.; this is not commonly found in the horse gut, but can cause colitis 

Risk factors for this condition include lowered immunity due to illness, stress or other conditions and previous treatment with antimicrobial drugs.

Your veterinarian will carefully examine your horse, performing a head to tail examination. During this time, they will carefully listen to the heart, lungs and gastrointestinal tract wgich may reveal hypermotile intestinal sounds, typical of bacterial diarrhea. Your veterinarian may also choose to perform the following diagnostic tests:

• Blood test for complete blood count to measure leukocytes in the blood
• Serum chemistry for protein and electrolyte levels
• Blood testing to check for acidosis
• Fecal cultures may be performed on stool samples (multiple samples may be required due to intermittent shedding)
• Clostridum types A and B are identified using immunoassays that detect toxins or cytotoxicity in cell culture
• Clostridum type C is usually detected through fecal culture

Intravenous fluid therapy to correct fluid loss and support blood pressure may be strongly indicated. Anti-inflammatories may be provided to help reduce gut inflammation and pain, though as risks to the renal system are present with this medication, this will be used carefully. 

Antimicrobals may be considered in the treatment of your pet, with metronidazole being indicated for horses who have had Clostridium identified as the cause. This is given via the mouth every 12 hours.  

Electrolyte supplementation will be given if indicated by serum chemistry results. Your horse may also be given gastrointestinal protectants such as biosponge or activated charcoal. If endotoxemia has occurred further, carefully monitored treatment may be required which may include anti-endotoxin serum.

Further steps of supportive care you can offer your horse are:

• Braiding your horse’s tail to reduce accumulation of diarrheal material on the hair 
• Clean your horse’s hindquarters with warm water and apply a barrier cream to prevent irritation and burning
• Reduce stress if possible
• Support your horse’s recovery by providing them with plenty of roughage and good quality hay
• As diet change in itself can cause colitis, prevent rapid change to the diet occurring 
• Probiotic therapy may be considered, however there is currently more research needed to support the use of this

The prognosis for your horse varies depending on the underlying cause of the condition.  Some horses may improve with minimal intervention, while others may require intensive care and hospitalisation. 

Prevention of the disease:

• Ensure your horse has access to clean drinking water and prevent access to contaminated waterways
• Ensure your horse is kept isolated and away from other horses during recovery

It should be noted that horse owners who have an equine companion with this condition must be aware that some bacteria pose a zoonotic risk. Ensure strict hygiene is practiced.