Cereal grains do not form part of the natural diet of equines, however, results from an initial survey conducted, suggest that horses in the Australian thoroughbred industry are currently being fed on average about 7 kg of grain concentrate/day. Horses are not well equipped to digest the starch from cereal grains in the small intestine and as a consequence, the hindgut fermentation of starch, which may lead to hindgut lactic acidosis and diseases such as laminitis, is an evident problem in the thoroughbred industry. Two main factors determine the extent of starch digestion that will occur in the equine small intestine. These are: 1. the attributes of cereal grains that determine starch digestibility; and 2. the ability of an individual horse to digest starch in the small intestine. The general hypothesis for this thesis was therefore that both the attributes of cereal grains that determine starch digestibility and the ability of individual horses to digest starch in the small intestine will determine how much cereal grain starch may be fed 'safely' before problems with hindgut starch fermentation and acidosis will be experienced. A series of experiments were conducted to test this hypothesis and to specifically examine the effect of grain species, grain processing and enzyme supplementation on small intestinal starch digestion in horses. Oats, barley, triticale, corn and rice were the cereal grains studied and expansion, extrusion, steam rolling and micronizing were the processing techniques investigated.