Fat exists in low levels in plants and can be added to increase the energy density of the diet. Fat has per kilogram of energy, which is 2.25 times that of any carbohydrate source. Because equids have no gall bladder to store large quantities of bile, which flows continuously from the liver directly into the small intestine, fat, though a necessary nutrient, is difficult for them to digest and utilize in large quantities. However, they are able to digest a greater amount of fat than can cattle. Horses benefit from up to 8% fat in their diets, but more does not always provide a visible benefit. Horses can only have 15-20% fat in their diet without the risk of developing diarrhea.