A horse’s faecal balls should be smooth, not too dry, and not too wet. When a horse has diarrhoea, a higher moisture content will make the faeces wetter and flatter. Another form of diarrhoea is watery stool, which often causes splattered stool water on the horse’s buttocks and tail. Nutrients and fluids are absorbed in the hindgut.

The amount absorbed depends on the speed of passage and the quality of the intestinal wall. If food passes too quickly, there won’t be enough time for nutrients to be absorbed. This may be brought on by stress (for example from transport), a change of feed which disrupts the gut flora, or dental problems preventing the horse from chewing his feed adequately.

Disturbed intake is often caused by an inflammation due to sand in the intestine (wounds), parasites (worm infestations), or bacterial or viral infections.
If your horse has diarrhoea, make sure he gets enough fluids and consult a vet if necessary.