Did you put him on the Vit E & Selenium or did his previous owner do that?
What was the reasoning?
Nothing wrong with Vitamin E as it boosts the immune system.
Selenium can be toxic. I know that pastures in some areas of the United States are very low in selenium and horses can be supplemented.
Selenium is also high in other areas of the United States and horses should NOT be supplemented.
My area is "just a tch" low and I do not supplement. My horses get enough in their vit/min supplements.
You also didn't mention what else this horse is being fed. If it's getting bagged feed, a certain amount of selenium has been added in.
The best thing to do would be to ask your vet if the Vit E/selenium is necessary for the living conditions your horse is in.
Vitamins and minerals should not be added to a horse's diet "just because someone said to" or because the previous Owner thought it was a good idea.
This is as much about helping the horse maintain good health (without over doing the supplements) as it is about saving money
Hope this helps.