I have a pullet about 4 months old, she has 3 other siblings they are American game breed, They have all been healthy and running free range with other chickens adults and youngsters since hatched by hen, on Monday of this week I noticed she was making noise like she had something caught in her throat, she'd walk around with her mouth open and then make a strange noise, we checked her out throughly no impacted crop and nothing stuck in her throat, she was eating and drinking fine, now this morning she can't walk has one foot drawn up and still has her mouth open like she's having trouble breathing. she's doesn't seem to be in distress about breathing though. Her feathers a very shiny and her eyes are clear, she makes me think of someone who has had a stroke with her foot drawn up, if anyone has experienced this before I would sure appreciate some info. We are thinking we should put her to sleep, it's hard to know if she is suffering.None of my other 22 chickens are having problems. Could it be a birth defect that is just now showing up? Thanks