If they're not walking, stumbling, unable to stand etc, and look Really sick I would say Botulism. If they're not walking, etc, and otherwise have a normal expression on their face, and don't look sick, I would say Marek's.
Before anything, I would do worming like Chickenzoo said , dust for mites, and give them vitamins, esp B vitamins like thiamine. And if you've treated for worms or mites this year, I would not think that's the problem , but it helps to eliminate as many causes as possible.
Before anything, I would do worming like Chickenzoo said , dust for mites, and give them vitamins, esp B vitamins like thiamine. And if you've treated for worms or mites this year, I would not think that's the problem , but it helps to eliminate as many causes as possible.