There's really not enough information about your horse here for anyone to give you any kind of advice as to his diet. :)
The first question that we should ask is: How much does your horse weigh? I recently stumbled across a handy calculator
, which should give you an approximate figure to go by. (:
Next, we should ask what his current condition is. Is he pleasantly plump? Or could he benefit from a few more pounds? Or maybe he's just about right! Pictures can be super helpful in determining this if you're not sure.
What is his work like? On a "not too hard" day for Mudpie, he's lounged with side reins for half an hour and then worked in walk, trot, and canter on the flat for an hour. Versus a "not too hard" day for someone else, which may be a leisurely trail ride, or maybe just a half hour ride around the arena. What does your ride typically consist of? :)
As for supplements, you'd have to look further into what it is that you want out of your supplements. It sounds like a supplement for respiratory health might be a good option! But your supplement plan should be uniquely designed to your horse.
:) Let us know, so that we can accurately help you out!