What you are dealing with is one of the most insidious and virulent bacterium we humans may face. C. perfringens is FAST. It's always present in chicken intestines to a small degree and also present everywhere in the soil. As long as it remains small in numbers and stays put, it can do no harm.
However, let a few coccidia protozoa move into the chicken's intestines and begin to multiply and start doing their damage to the chicken, C. perfringens is quick to take advantage of the breach in the intestinal lining the coccidia have begun.
C. perfringens begins to rapidly, and the key word is RAPID, drill down deep into the mucous lining of the intestine to start feeding on all the juicy proteins. The damage is devastating, sort of like a forest fire destroying a large swath of prime forest. Just as the fire destroys and kills and blackens, so does the lightening speed of C. perfringens destroy deep into the intestines.
Once the tissue is killed, it turns necrotic, lost for good. About the only thing that can save a chicken is to recognize it early and begin antibiotic treatment. I've had experience with this monster and I've seen how fast it kills. A ten month old Cream Legbar, just beginning to lay, became sick late one morning, and she was dead by early afternoon. A week later, I recognized the symptoms when her brooder mate became sick. I moved fast and started her on amoxcillin and she's alive and well four years later to tell about it.
When I notice a chicken acting "off", acting sluggish, nodding off standing up, that's when I move into action. I have antibiotics on hand all the time. When there's a possibility of C. perfringens, it's okay to jump right in with an antibiotic. If it turns out to be a stuck egg or something that normally can be treated without an antibiotic, great. I simply stop the antibiotic and treat for the other thing.
When we see that coccidiosis may be sickening a chicken, we immediately begin treatment of the whole flock with a coccidiostat (Corid). If the chicken is acting particularly lethargic, even though there may not be blood in the stool, necrotic enteritis (NE) should be assumed, and an antibiotic should be started immediately. It's the only way to win when dealing with this diabolical monster. If we hesitate even a few hours, it can be too late to stop irreversible damage.
Do your chickens have irreversible NE damage? About the only way you will know is if the chicken lives or if it dies. If you've treated the chicken for the specified duration for that antibiotic, treating longer won't accomplish anything. The bacteria likely has been killed, but if the damage to the intestines is severe, nothing can restore the intestine any more than putting out the fire will bring back the forest.
