Five day old chicks dying one by one. Seem fine then become lethargic, get a glazed look, wobbly on their legs, refuse to eat/drink, then die. At least one seems to be struggling to breathe with mouth opening and closing. Only one had pasty butt and we have been looking out for it so it doesn’t seem related. Temperature is fine, brooders worked fine for around 50 chicks last year. They’re not all the same breed as each other. My younger brothers are on the verge of having a melt down because they’re trying to help but nothing seems to help once they get sick. We’ve lost 5 so far with a sixth looking sick as well. Any good ideas?