I found two of my meat chickens lethargic, breathing heavy, eyes closed, unable to stand one was further gone then the other and has now died. The other I have separated from the group but I am not too hopeful. I have given scrambled eggs and probiotic but it doesn't want to eat or drink. Several of my other meat birds that are not sick yet, have poop all over their feathers by their vents. I have added probiotics, electrolytes to water for them. These are slow white broilers and are 7 1/2 weeks old. We are about 3 weeks away from butchering. I feed no soy no corn organic feed with 22% protein from Modesto Milling here in CA. I did have to give a Scratch n Peck feed last week cause the feed store was out of the other. What do you think this could be and what should I be doing?