The horse digests fat well, when consumed in moderate quantities. If we give vegetable oil in the ration, we expect that it is unproblematic to give up to 0.10 kg per 100 kg of body weight. This means that we could give 0.5 litres per day to a horse of 500 kg. The oil should be divided into at least two meals. The horse is not particularly fond of vegetable oil. You will therefore have to mix the oil with feeds that the horse will eat readily, such as grain or concentrates.
Fat is rich in energy, and usually contains around three times as much energy as conventional feed mixtures. This means that 0.3 kg of oil has about the same energy value as 1 kg of concentrates.