I'm so confused My chicks range from 8 weeks to 15 weeks. When I bought the older chicks...1 just never seemed right. She was always tired & then couldn't use one of her legs. After much effort to save her with vitamins etc. weeks later she died. After she died another one acted the same way & died etc. They start out acting totally fine, then all of a sudden act tired all the time, some seem to display hurt legs that turn stiff & some don't. Some will then lay on there sides & be dead the next day & some just seem to stay alive for weeks & weeks. They all get the same brand food..vitamins..grit etc. I even switched my feed thinking my feed might of had something to do with it but apparently not. I make them scrambled eggs, bought them plain yogurt, watermelon etc. They get plenty of fresh water & grass everyday. My bedding is cleaned daily of pine shavings. They have a very nice place to live with plenty of room & perches. My oldest chicks were never vaccinated for Mareks disease but the younger ones all were & the younger ones are still getting sick so I dont think its that. They all got 2 weeks of medicated water for cocci when they arrived here. What is going on???? Does anyone have any ideas?