HELP! New chicken owner here. My first flock of Buff Orpington pullets is already in trouble after only 5 months. My head pullet started separating herself from the other birds. She wouldn't eat with them and started hiding. I noticed she had lost some weight, had runny stool and was quite pale. She was found dead this morning. I have 2 other pullets that are the same age (about 5 months) and they are both exhibiting normal behavior, but one of them also has runny stool now. I'm concerned if I don't take action she may have the same fate. There is no sign of injury on any of the birds. My neighbors do spray chemicals in their yard and since we've had lots of rain, I'm concerned some of it may have washed into my yard or potentially they ate bugs that were contaminated? The birds all free range during the day and they are being fed 50/50 medicated chick starter and layer feed as well. The birds were not vaccinated. I've considered the possibility of this being coccidiosis, but I thought the medicated starter feed would prevent that. I have Amprolium on hand. Should I feed this to the remaining birds as a precaution? What can I do?