Looks like he was famous for his round barn. With all Dougan's history in Wis. plus his grandaughter's books the bottle may have some value. If it isn't too common.
Hey Sode, I would love to help in any way that I can. I am a Wisconsin bottle collector and nut. Feel free to email or PM me. Unfortunately, I know far less about milks than other categories. I do know some milk collectors but I don't see them all that often. As for mrbottles, the gentelman who runs the site has very little interest in milks. It might be nice if he at least responded but I think you are correct not to hold your breath waiting for replies.
Generally speaking. Here are some more ideas on value. Condition always helps. Minty is good. Perfect applied colored labels are a must. Small towns are better than bigger ones but small companies from big towns might be good. Embossed pictures such as animals or scenes are very desireable. I personally like the ones that say 5 cent store bottle but it must include a town and dairy or it is not rare. Unique features like the 'ribs' in the bottle above can help as well. Hope everything goes well. If you try to sell them say on ebay, be sure to list as many details as you can so, that they are easily found in searches. Best of luck. Bob