Droopy tail and wings. The slow decline

[azygous]

Delay, as you suspect, can be deadly where coccidiosis is concerned. The thing about Corid treatment is that it's never the wrong call to go ahead and treat if you suspect coccidiosis. All it does is block a particular B vitamin that coccidia feed on in order to complete their life cycle. Depriving the coccidia of this nutrient early enough can make a huge difference.

However, making the treatment a regular practice would be counter productive as it could set up a thiamine deficiency in the chickens, and that could have its own serious consequences. A better practice would be to use the "preventative" formula for a much lighter Corid dose that wouldn't present this danger.

Another option that not too many folks are aware of is that for a very sick chicken you can use a Corid "drench" formula in addition to the Corid water treatment. This way a sick chicken gets a focused exposure to the Corid treatment for faster recovery. It's .1ml per pound of body weight of undiluted liquid Corid given by oral syringe.

In some cases where a chicken is very sick and perhaps having bloody stools, you might also want to use an antibiotic along with the Corid treatment to knock out any secondary bacterial infection that is eroding the intestinal lining. Sulfa drugs are the antibiotic of choice for this purpose. Given early enough, it can save a chicken's life.

 

[Castlewood]

UPDATE:
Something that should have been expected, a second bird began showing some symptoms. I think we caught it early or earlier than the poor girl that died.
This second pullet is the same age as the first, 4 months. I've quarantined her from the rest. They are all on a week's worth of Corid-20. The flock seems to be doing well. This isolated pullet is weak but alive. She's lost a LOT of weight and doesnt have much strength but she's alert and not in a zombie state.

I've giving her water by syringe in the morning and evening just to make sure that she gets enough hydration each day. Is there anything that I can do to get some calories into her? She eats, but not much each day

 

[azygous]

Offer her boiled egg, cottage cheese, tofu, boiled rice, canned mackerel or tuna, baby food. One at at a time, not all at once. I've found that my sick chickens like dry crumbles, a change from their normal fermented feed. Anything different can tempt a sick chicken.

 

[Castlewood]

Circling back to update: after losing multiple chickens, we've finally identified the culprit as Mareks. Necropsy at the Texas A&M DVML lab in Gonzales has confirmed. So at least now we know.

@azygous thank you for all your input! Reading back through this thread has been educational, yet again.