HollowOfWisps
Previously AstroDuck
I would have a hard time trusting a vet that is throwing around such a serious disease diagnosis as marek's without it being confirmed through testing. I also agree that vitamin deficiencies are often seen throughout a flock because your flock is eating the same feed and will therefore be missing the same nutrients. I'm curious are you feeding a whole grain feed? Also something as simple as a piece of feed that was laying on the ground and got moldy then eaten can cause botulism.