Why open-top troughs?
Open top troughs allow something like 100 times as much area for feeding as do troughs with lids and lick wheels. This makes it possible to eliminate overeating by a few aggressive animals at the expense of other less aggressive animals for a much more true average consumption. This improves total herd performance. Most other liquid products are not fed in open troughs, because of the danger and costs that come from overeating.