Diarrhoea in horses can be dangerous and difficult to treat. Most horse diarrhoea is short lived and causes little concern but when the lining of the gut is damaged and serious infection sets in horses can loose a lot of weight quickly and become permanently damaged. The most dangerous cause of diarrhoea is salmonella infections.
Call your vet if: your horse is off colour and has a temperature, if the diarrhoea persists for more than a day or two, if a foal is affected at all.
Common causes: Stress/nerves. Sudden change of feed, serious infections eg salmonella, worms, prolonged antibiotic use.
Treatment: A vet will first try and determine the cause and attempt to remove it. It is very important that lost fluids are replaced by giving fluids and drugs may be used which slow down the passage of food through the gut. Probiotics are often useful to try and regain normal bacterial populations in the gut. Horses affected should be fed good quality hay and normally not allowed fresh grazing or succulent feeds.
Many horses that suffer from diarrhoea, particularly young horses in the spring time, do so because of small redworm infection. In particular, it is the larval stages of this parasite that cause problems. During the grazing season horses can accumulate tens of thousands of larvae within their gut walls. These larvae go into a state of arrested development or "hibernation." At a later time, often in the spring, the larvae will re-activate or wake up from hibernation and erupt out of the gut wall. If tens of thousands of larvae all do this at the same time it causes massive damage to the gut wall leading to diarrhoea, weight loss and sometimes death. This is a particularly difficult condition for veterinary surgeons because:
It is difficult to diagnose
The drugs available are not very effective at treating it
It is difficult to detect the build up of larvae in the gut wall
A significant proportion of horses with this condition will die in spite of intensive veterinary treatment.
Some horses with heavy small redworm burdens will suffer from weight loss, poor condition and failure to grow without developing diarrhoea. These problems can arise without the larvae erupting from the gut wall. The exact pathological mechanism by which this occurs is poorly understood at present.