We use Wind and Rain. We keep it out year round, but the stuff with the fly control in it we started putting out in Feb, last year which was a very cold year so this year may be different. Our cows do not border any other herds outside our own. So i watched near by herds i knew werent getting any kind of fly control. After feeding it months, by around june, we were hit with flies with vengeance both years. We rarely spray our cows, but we had to get them up twice and spray for flies. Neighboring herds had flies just the same... This was the second year we've used it, and both years we had flies pretty bad.
We bought most of ours with a 15% off coupon at TSC by the pallet and got it for around $33 a bag.. I started mixing it with a little salt because the cows were eating it so fast. They require so many oz a day, but they were eating about a pound a day... I'd put a 50 pound bag out in a heard of less than 50 and they'd eat it in a few hours.. I started mixing part of a bag of white salt with it, and it'd last a couple days.