2 of my 4 month old chickens died recently wiithin 2 weeks of each other. Both had been eating and drinking well but I noticed they were reallly thin when I separated them from the other chickens. The most recent one to die had diarrhea too - not sure about the first one. I separated them when I noticed they were acting differently - being lethargic, not going outside with the others, hanging out by themselves away from the others. There were no other signs of illness that I noticed. They both died within days of my noticing the lethargy. Does anyone have ideas what it could have been? I had an older hen who was quiet and lethargic about 6 weeks ago - gave her some antibiotics and she recovered quickly. BUT in early Sept their sister had to be put to sleep because she couldn't stand on one of her legs - she could only push herself around with her good leg. I thought maybe Marek's but she was really perky and eating and drinking fine for about 5 days (I had her in a sling) before I took her to my avian vet. My vet thought she injured her spinal cord causing the paralysis based on a physical exam. She is an experience and certified avain vet. Priior to this, another person familiar with birds examined her and though it was a spinal cord injury. Based on my reading, I thought Marek's would be recognizable based on limping and/or paralysis. Does it ever just cause lethargy and failure to gain weight? The birds I've mentioned were not vaccinated and a few new birds have been added to my flock within the time frame mentioned. There are 5 birds remaining from this clutch and so far they appear to be acting normally. Any ideas what it might be happening? Could it have been Marek's? I'm pretty new to chickens so any thoughts would be appreciated.