Hi I am new to chickens I got 50 chicks in oct. they all did fine I didn't lose any. When they were 4 months old I put them on layer pellets. free choice grit and cal. One day I went out and one chicken looked like she had a hurt foot she could not stand. I moved her to a small box and gave her food and water. she was eating and drinking fine when I went to bed. she died durning the night. I thought she had gotten hurt. about two days later there was another one that couldnt walk. samething eating and drinking fine died durning the night. called my vet he does not deal with chickens but gave me an antibiotic to use. used it for ten days every one was fine then three days after I stopped another chicken cant walk and died over night. They are in a new coop that was built just for them. it is 12 by 16 I use pine shavings and clean it out once a week. not sure what to do there poop is normal.