COLITIS – THE FIVE MAIN CAUSES
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Colitis is inflammation of the large or small colon that can lead to diarrhoea and associated loss of fluid and salt, proliferation of harmful bacteria, and even death in severe cases. This potentially life-threatening condition can arise from various causes, but unfortunately, it is often difficult to pinpoint precisely which is the main instigating factor.
Presentation of colitis
Horses with colitis often present with diarrhoea, colic, a lack of appetite, and lethargy. Diarrhoea is not present in all cases, however, and some simply present with fever and weight loss or general poor condition.
The causes
Five of the most common culprits include:
- Infectious agents. These colitis-causing agents include pathogens such as Salmonella, Clostridium difficile, Clostridium perfringens, coronavirus, and Neorickettsia risticii. These bacteria can enter the horse’s system through contaminated feed, water or exposure to infected animals.
- Parasites.Parasitic infestation, particularly by small strongyles, also called cyathostomins, can cause colitis. As part of the normal life cycle of small strongyles, the third-stage larvae (L3) migrate into the walls of the intestine in the caecum and colon. Once they mature (which takes months to years), the fourth-stage larvae (L4) migrate back into the lumen of the intestine as luminal L4 before they reach the final and sexually mature stage (L5). Horses can harbour hundreds of thousands of encysted larvae in the L4 stage, and if these larvae emerge all at once, the inflammation of the caecum and the colon (colitis) can result in severe diarrhoea.
- Antibiotic-associated diarrhoea. Any medication, particularly antibiotics, can upset the ecosystem of microbes living in the horse’s gut (the microbiome), thereby causing diarrhoea. The antibiotics ceftiofur sodium and trimethoprim sulfadiazine (Purbac) are among the most common causes of antibiotic-associated diarrhoea, but they are also the most commonly prescribed antibiotics in horses, so the association may simply reflect the frequency of use.
- Non-steroidal anti-inflammatory drug (NSAID)-associated diarrhoea. Some horses develop diarrhoea caused by ulceration of the lining of the large colon following the administration of non-steroidal anti-inflammatory drugs (NSAIDs) and flunixin meglumine (Finadyne). The right dorsal colon appears particularly prone to ulceration, though the reason for this is unknown. Vets also don’t know why certain horses have this response to NSAIDs while others do not. Dehydration, however, might increase the risk of damage.
- Indiscriminate (random) causes. These include dietary imbalances, sand impactions, malignancy, food allergies, toxin ingestion, and inflammatory bowel disease, among others.
Did you know?
In cases where the cause of the colitis is not determined, it is termed idiopathic colitis.
Take home message
Regardless of the cause, if your horse has persistent or significant diarrhoea, contact your vet immediately so that potentially life-saving treatment can be initiated as soon as possible.