I thought I should share that I saw one looking a little off a few days ago and last night I decided to bring her in. Her poop looks very much like the poop pictures I posted, so I suspect it's blackhead and E.coli, though I guess it could be something else. Doesn't matter though, treatment will be the same.
2.5 year old 3 kg hen
0.6m (60mg)l Baytril (100mg/ml) by injection once a day
100 mg metronidazole orally twice a day for no less than 5 days
1.5 ml Safeguard orally once a day for 5 days
0.7 ml Corid orally once a day for 5 days
60-120ml of fluids via the tube several times a day. Once hydrated I will tube Kaytee.
So sorry... blackhead can spread through the whole flock. It doesn't always, but it can. All should be de-wormed and you should buy enough metronidazole and Baytri to treat all of them in case they do get sick.