It's my understanding that trough feeders for deer promote the transmission of diseases such as bovine tuberculosis. Supposedly, an infected deer that comes to the trough, drools on the feed, and other deer come and ingest it, along with the grain. The disease is transmitted via bodily fluids. At least, that's the explanation the State of MI gave out, when they were allowing baiting and feeding of deer. They were specific on the amount of feed or bait you could put out at one time, and it had to be spread over a certain area. the bait or feed could not be concentrated, as in a trough or in a pile.