As a starting point, feed forage at about 1.5 to 2.5 percent of bodyweight per day. For a typical 500 kg horse that is roughly 7.5 to 12.5 kg of hay daily, adjusted for grass, work and condition.
Work from bodyweight
Horses evolved to eat little and often, so forage should make up the bulk of the diet. A common guideline is 1.5 to 2.5 percent of bodyweight in dry forage per day. Weigh your hay with a luggage scale rather than guessing by the flake, because flakes vary a lot in weight.
Account for grazing
If your horse is out on good grass, it is already eating forage, so stabled hay can be reduced. In winter, or on bare paddocks, hay may need to make up almost the entire forage ration. Change amounts gradually over several days to protect the gut.
Slow the eating down
A horse that bolts a hay ration and then stands for hours with an empty stomach is at higher risk of ulcers and boredom vices. A small-holed hay net or slow feeder makes a ration last far longer and keeps the gut working. See our best slow feeder hay bags.
Adjust for the individual
Hard keepers and horses in heavy work may need the upper end plus extra calories. Good doers and native breeds prone to laminitis often need soaked or lower-sugar hay and careful limits. Body condition scoring every couple of weeks tells you if you have the balance right.
Never cut forage too low
Dropping forage below about 1.5 percent of bodyweight to control weight is risky and can trigger gut problems. Instead choose lower-calorie hay, soak it to reduce sugar, and use a slow feeder so the same weight lasts longer.
