I had 6 cuckoo marans mixed into my flock. 4 of them have died over the last year with the same ailments; starts with a sneeze or 2, then wheezing breathing, then within a day they are dead. I feed them layer crumbles, fruit, veggies, bread, ac vinegar in their water and have been giving them "sav-a chick" for about a week now as a rat(s) spread something through my coop. Are respiratory issues common for the breed, is there something I've done wrong? i have roughly 25 other chickens and none of the other breeds have had this happen. The one that passed today was healthy 2 days ago, yesterday sneezed a few times, and dropped dead about 15 min ago. She was clear eyed, had no nasal discharge, was eating and drinking, did not feel like she was thin or had lost any weight or anything abnormal. Is this possibly something I should be treating my other chickens for? I use pine shavings in my coops and use hay to bed my nesting boxes.