Milled flax seed.
As proven by a University of Guelph study, dietary supplementation with flax stimulates a horses immune system, relieves arthritis and reduces pain due to inflammation. It increases the ability of cells to take up oxygen, as well as improve skin and hair coat.
Because it is high in dietary fiber, it can also help prevent impaction and sand colics. Horses suffering from Sweet Itch improve dramatically when supplemented daily with milled flax seed meal.