CHICKEN GASPING FOR AIR

[Backcountrychickens]

Hello all. I have a 3 year old white leghorn hen who has been gaping for breath for about 2 weeks now, but she seems to be worse. She is weak but is still able to walk around, her crop is full, and she has been pooping, but her stool was small. She will arch her neck and wheeze with her mouth open, making a squeaking sound and sticking her tongue out. She has no visible issues (no mites or lumps or injuries) exept that her comb looks slightly discolored (purple ish). We also have had no previous issues with mareks, and about half of our hens are vaccinated for it. All of our hens are feee range.
Should i just cull her?
Thanks.

 

[azygous]

No, do not cull until we figure out what's going on.

Have you looked into her throat and in her ears with a strong flashlight?

Are her nares clogged with scar tissue so she can't breathe through the beak holes?

What does her poop look like? Runny, watery, green, brown, unusually smelly?

What is the weather like there? Has it been unusually hot?