Fats are nearly completely utilised as they are usually more than 90% digestible. Both fatty acids and glycerol are predominantly absorbed in the jejunum and ileum. When large concentrations of fat are included in the diet e.g. of horses used for long distance riding, it is important to restrict the amounts so that the digestive capacity of the small intestine is not exceeded, since long-chain fatty acids (C16, C18 and above) are not absorbed in the hind gut. Excess fats which are transferred to the hind gut may reduce the digestion of fibrous carbohydrate. It is therefore strongly recommended to divide larger quantities of fats (vegetable oils at the rate of 0.5 litre or more per day) over several meals during the day.
Carbohydrates are fermented by microbes to short-chain fatty acids which are then absorbed in the caecum and colon. Fats cannot form glucose in the body of the horse, but must be utilised directly as an energy source or stored temporarily in the fat depots for later use. Because fats are not transformed into carbohydrate and stored as glycogen in the muscles, they are beneficial for horses that are prone to myoglobinuria and benefit from a larger proportion of their energy requirements being given as fats. Both myoglobinuria and some other muscle problems are related to the accumulation of large deposits of glycogen in the muscles. In particular, horses that are receiving large amounts of grains or commercial concentrates are prone to contracting myoglobinuria when exercise levels are reduced for several consecutive days without restricting their intake.