What cuties! I'm glad they seem to be getting over what may well be infectious bronchitis. IB is easily spread to 100% of the flock. I would'nt breed any more or hatch eggs for a year, and it provably will be ended. The literature says that IB exposed birds remain carriers for 5 months to a year.
If you can post a picture of the red mucus in the droppings it might be helpful. Intestinal shed looks more like strings of orangey red tomatoes than blood, which is usually red or pinkish. Blood can look like red berries, and is a sign of coccidiosis. Not all strains of cocci cause blood in...
No, I wouldn't treat them any longer than 14 days on the Duramycin. If any look particularly sick, you can use some Tylan 50 injectable, but give it orally to each chick, 1/4 ml twice a day for 3-5 days. Again if it is IB, the antibiotics may not help, so I would just give it if they are much...
Since they didn't respond to the antibiotics, it probably is a virus, probably IB since it spread to most of the chicks. Infectious bronchitis is one that lasts around a month, and includes sneezing. It is much harder on chicks than grown chickens. One good thing about the antibiotics is that...