What do oats do for horses?
First of all, horses LOVE oats, so they enjoy eating them. Oats are also used to give a horse more energy for working horses and supplements and sometimes dewormer is often mixed in with the grain because most horse's won't eat most dewormers or supplements unless they are added to something tasty, like grain.
Oats should only be fed to horses in moderate or harder work, or those that have trouble keeping weight on. Some horses will no do well on oats and may develop laminitis/ founder, or any other number of problems could crop up. The amount of oats fed will depend on the horse's age, weight, workload, and health status. There is no one amount of oats that is correct for all horses.
The amount of oats you feed depends on the horses age, level of work, and caloric needs. Oats are high energy, but they can cause problems with horses. You should never feed more than 6 pounds in one day unless a equine veterinarian approves it. Most bags of horse oats will have feeding instructions on them.