The smell from and poultry farm depends on proximity and prevailing winds. If the subect property is located West of the farm, chances are any smells will be minimized. Winds do "swirl" at times, even then...it depends on what is going on at the poultry farm. If the chickens are in the Grow-out stage, the smell will be pretty much contained in the barn, If the barn is in a clean-out stage ( the birds have been emptied from the barns and delivered to the processing plant) then that will be the time that any odor will be "traveling with the wind" During clean-out, all the sawdust on the floor of the barn is scraped out and hauled away. Stuff is sturred-up and therefore the bouquet has a beter chance of being airborn.
Clean outs usually take one to two days.
The question as to what is in the barns needs to be addressed. Chickens are not so bad as far a smells go...turkeys, that is another matter. There are a few Quail barns in Union County. I have been inside a barn with 25,000 adult Quail birds inside, the smell so so slight, you could eat your lunch in there. Not that you would want to, is still a bit dusty inside.
In Union County, NC...you do net need to live near a barn to share is the smells of poultry barns. Remember the sawduse collected in the clean-out? Well, it is packed full of nitrogen rich poo, the farmers just loooove to spread that mixture on their crop fields. That smell will last only a day or two, unless a hard rain packs in down, thus reducing the smell factor altogether.If you are considering a particuler property, I would be glad to "map-it-out" for you and help determing a smell-assessment.
I just read Alan May's comment...he has aparently never been near a Turkey Barn....