Early symptoms of blackhead are sleepiness, not as vigorous and eager to forage, going off feed (poor appetite), droopy wings, and indifference to being handled. In the later stages of the illness they don't try to get away when you try to handle them. In the early days of the illness they will still run and make an effort to get away. I've noticed mine get very liquid diarrhea early on, probably from reduced feed intake. The yellow droppings are a late symptom. Mine have never stopped drinking water while being ill so I've not had the need to tube feed. They go off feed but that doesn't worry me as much as not getting any water. By about day 3 of treatment is when I've found their appetite returns.