Considering your location, are the cows still grazing the grass or just on it? You can do a split application. Lime 40 acres, and leave the other hald alone for about a week. This may or may not help if the cows get curious, but if you could run a strand of electric across, it would keep them from inhaling it. Also, you can have the liming timed to be put one a day or so before a shower. Wouldn't have to be much, just enough to get the dust settled off the leaves.