I have lost 2 chickens in 2 weeks. I had a small flock of only 4 and they aren't around any other birds. The first one I noticed she wasn't as perkyas she usually was and she had stopped laying. 2 weeks later we lost another and her symptoms word lethargy, lack of appetite and her crop was full and mushy. We brought her inside and kept her under heat lamp. I tried to massage for crop and make her vomit but nothing came out. Any suggestions as to what could be plaguing my chickens?