Food allergies are caused by the body's immune system mistaking a specific type of protein as harmful. Most often, the immune system will produce specific antibodies to 'fight off' the offending allergen. This results in chemicals, such as histamine being produced, which cause inflammation.
Skin prick tests can be used to determine potential allergen(s), but studies have proven this to be an unreliable method of testing. If a genuine food allergy is suspected, an elimination diet is usually the best course of action.
An elimination diet involves removing all feed and supplements (except forage) from the horse's diet for a period of 4-6 weeks. If the ‘reaction’ (hives, itching etc.) disappears, individual feeds/ ingredients are the introduced one at a time to see if it returns.
Sometimes horses suffer from food intolerances rather than allergies, which are not caused by the immune system (and aren't life threatening). Intolerances in horses are very difficult to diagnose. Symptoms generally take several hours or sometimes days to develop and in most cases, it takes larger quantities of the given food/ ingredient to cause a reaction. Food intolerances in horses are thought to be extremely rare but if suspected, an elimination diet is again the best course of action.
It’s a balancing act to manage the diet of horses and ponies. This careful management is best left to the owners as interfering with their routine or the food they consume can cause them harm.