Something to consider outside of "paint" is the use of a Spar Urethane such as that produced by Helmsman (MinWax). It can be purchased at Lowes or Home Depot and comes in a variety of sheens, designed to seal and protect wood surfaces. Something to remember for the sheen is: the higher the gloss, the tighter the finish. A high gloss will be easier to clean and have less penetration from surface contaminents than a satin, but will also have a shiny look that some may not like. Also, the more coats, the higher the sheen.
We used Helmsman Spar Urethane Gloss (red label on can) on all interior surfaces of our barn (for horses). As a result, we could completely hose down the barn interior with no damage to the wood. The result has left our year old barn looking brand new compared to that of a friend that looks well worn (at the same age). Also, once the product cures (after 24 hours), the animals could eat clean through the barn without adverse effect. We own a historic restoration company and did extensive research during barn construction.
We plan to do this to our coop interior, as well.