Supplementation of vitamin E is essential for most horses because they cannot internally generate it, like they can other vitamins. In order to naturally receive adequate amounts of vitamin E, horses typically need to be on grass pasture for at least 12 hours a day, year round. For horses in sand lots, or on restricted pasture, Vitamin E supplementation can be crucial for them to thrive.
*WARNING: Avoid mixing any Vitamin E supplement with Iron supplements (hematinic) as this may negatively affect absorption rates of the vitamins. If you feed an Iron supplement along with Vitamin E, it is recommended that you feed them in separate doses (i.e., Vit E supplement in the morning and Iron supplement in the evening); this pattern avoids destroying the uptake of either supplement.