I lost a Buff Orp from a good breeder that we tried for two months to save. She laid maybe three or four eggs, then quit and began losing weight. She refused to eat the pellets anymore. We did special feedings of yogurt, salmon and oatmeal/grits, vitamins, changed her feed to crumble which she ate for awhile, etc, consulted experts, and she was just bones and feathers and in the end, just refused food and water. It wasn't pests at all. Seemed as if it was some health issue within her alone that was triggered by her coming into lay, which she did at around 34 weeks old. She died before her first year birthday. It was a complete mystery. Sometimes, if it's internal, some insufficiency in a single bird you just can't see, you never find the cause, unless you get a professional necropsy done.