Every 5 seconds, a mount will automatically eat food from your offhand if it is damaged and the food is appropriate for the mount. (Horses eat #horse_food, striders eat #strider_food, happy ghasts eat #happy_ghast_food) This results in half a heart worth of healing for your mount.
This applies to these mobs: Horses, Donkeys, Mules, Llamas, Trader Llamas, Camels, Striders, Happy Ghasts.
/scoreboard players set AllowUndeadMountsToEat OffhandHarvHorseSettings 1
This is a "setting" that lets you make it work for skeleton horses and zombie horses too. Noteably, undead mounst heal for more as they use the instant damage effect.
/scoreboard players set AllowMountsToEatWithoutDamage OffhandhandHarvHorseSettings 1
This is a "setting" that allows mounts to eat even if they are at full health.
