Cattle, flies and Fly tub affect on chickens

We recently purchased a few steer and they were being eaten pretty badly by flies. My ultimate goal is to manage this with our chickens (need to build them a mobile coop), build bird houses and buy wasps. However, we were heading on a trip and needed to start something to get them more comfortable. We put an Altosid fly tub (yes, I know - yucky) in with them and set up some fly traps. I realize this takes a bit to work but needed to get something started. My biggest question is how long do I need to wait to put the chickens in the field, after removing the fly tub? Also, does anyone have a simple bird house plan? Any tips on doing this effectively but cheaper? Can anyone tell me about the blue sticky tarps?