Dairy barn trapping is not very fruitful,there is too much free feed around for a trap to be effective,a drop net is more productive,as well as flashlights and a net.I never got a single bird in a trap at a dairy,I got more than enough with a flashlight and a net.Dairy guys are kind of particular about rummaging around through the barn in the darkness,potential stress on the cows.My uncles have a feedlot barn so permission was never an issue.