Very sick Sebright chick- lethargic, heavy breathing, disheveled

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So I just got home from a bunch of medical appointments and one of my chicks is sick. She seemed fine this morning!

Approx 5wk Sebright. Lethargic, breathing heavily, feathers all ruffled and disheveled. Won’t open eyes. Sometimes makes noise when breathing, like a slight wheeze. Moves legs if I touch them, but not its feet/toes. Is this Mareks??? what should I do??

 

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I’ve tried to give some sugar water but she won’t even try to take it. Should I try to force a drop or two?

 

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Also, I’ve just noticed she has like a little bubble under her wing! All the other chicks are acting normally. I have her separated from the others.

 

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Ugh sorry to keep updating. Her keel is also very prominent and is visible. I don’t know what to think. I just introduced chick grit yesterday, could that have caused an issue? Her crop is soft but doesn’t feel empty.

 

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Welp, she didn’t make it

I’m going to scrub the brooder box really well, is there anything else I should do to help keep the rest of the babies from catching whatever she had? (I’m assuming it was an illness and not some random health defect)