It's SO important to get a real diagnosis if there's a possibility that it's a flock-culling thing.
Because there are certain diseases that are Big Baddies, and we all know about them, there's a temptation (on this discussion board and others) to label any possible fit symptoms-wise as one of those Big Baddies. Coryza, Mareks, etc. I've read hundreds of these threads. Most (I would say the overwhelming majority) of the chickens that everybody said MUST have one of the bad diseases, when they are taken for necropsy and diagnosis, don't test positive.
Chickens like to die. They like to die of a ton of stuff. And because they're animals with very little brain, they don't show subtle symptoms very well. The difference between a chicken dying of MG and a chicken dying of worms and a chicken dying of heat and a chicken dying of just plain cussedness is honestly not that huge. They lose color, they lose weight, they breathe badly, they start falling over, they drink too much water and so vomit when you pick them up, they end up not being able to move, and then they die. For ALL those things, and many more. That's why if you look at the Merck manual there's no diagnosis advice except necropsy, and why the big diagnostic departments at the universities are so important and so busy.
I've only ever been certain of coccidia when the bird is alive. That's because bloody poop is not part of that above list. Everything else, I have only known in hindsight, depending on what drug or change in conditions the flock responded to, or after testing.
