I am pretty much 100% sure one of my hens has gapeworm. I am a new chicken owner and had no idea they could get this from earthworms. My daughter and I found a bunch and fed our chickens about 2 months ago. She has been gaping for about a month and a half. At first it was infrequent and she acted normally. I thought it was respiratory and gave her antibiotics due to a rattle in her chest. She didn’t really improve so about 2 weeks later I gave another antibiotic shot. No improvement. I finally researched and found out about gapeworm. She holds her neck out, gurgles, and gasps for breath. I had some ivermectin and gave her a dose today. She is really struggling. When should I dose again? Also, should I dose my whole flock? And do I need to start a preventive maintanece with them as well?