I always try to prevent diseases, so I deworm my flock 2 times every year because they free range. I also feed medicated feed for chicks until they are 6 weeks old and give electrolytes in their water until they are 1-2 weeks old. I always keep chicken medications on hand and check for poop stuck on their feathers, mites/lice, abnormal behavior, egg laying amount, feed intake amount, and other things. I mainly use it for tracking purposes...Yeah, owning chickens involves a lot of death unfortunately. Reproductive disorders are common in chickens and can't be prevented. There are numerous other diseases that just happens even if their coop is predator proof...
Its always sad, its never easy when a chicken dies...