Laminitis has multiple causes, some of which commonly co-occur. These causes can be grouped into broad categories.
One of the more common causes. Current theory states that if a horse is given grain in excess or eats grass that is under stress and has accumulated excess non-structural carbohydrates (NSC, i.e. sugars, starch or fructan), it may be unable to digest all of the carbohydrate in the foregut. The excess then moves on to thehindgut and ferments in the cecum. The presence of this fermenting carbohydrate in the cecum causes proliferation of lactic acid bacteria and an increase in acidity. This process kills beneficial bacteria, which ferment fiber. The endotoxins and exotoxins may then be absorbed into the bloodstream, due to increased gut permeability, caused by irritation of the gut lining by increased acidity. The endotoxaemia results in impaired circulation, particularly in the feet. This results in laminitis.
Nitrogen compound overload
Herbivores are equipped to deal with a normal level of potentially-toxic non-protein nitrogen (NPN) compounds in their forage. If, for any reason, there is rapid upward fluctuation in levels of these compounds, for instance in lush spring growth on artificially fertilized lowland pasture, the natural metabolic processes can become overloaded, resulting in liver disturbance and toxic imbalance. For this reason, many avoid using artificial nitrogen fertilizer on horse pasture. If clover (or any legume) is allowed to dominate the pasture, this may also allow excess nitrogen to accumulate in forage, under stressful conditions such as frost or drought. Many weeds eaten by horses are nitrate accumulators. Direct ingestion of nitrate fertilizer material can also trigger laminitis, via a similar mechanism.