Unlike humans, horses can synthesise sufficient amounts of vitamin C in the large intestine. Furthermore, vitamin C is contained in feed, such as grass, hay and carrots. However, in horses that are exposed to high levels of sporting activity, the horse's own synthesis may not be sufficient - the same applies to horses that are exposed to constant stress.
Therefore, it is important to reduce stress and to prevent stomach ulcers in the long term, because these stress your horse even more - a vicious circle! This reduces the risk of vitamin C deficiency and, as a result, the risk of your horse catching an infection.