Excellent point, as does sprouting of seeds/grains. The sludge is normal and IMO one of the benefits. With dry feed, one ends up with a lot of fines the chickens don't eat. Thinking about the manufacturing process where grain is ground, essential nutrients and binders added then mixed, those fines contain many of the added trace minerals and vitamins to create a balanced feed. By the fines being suspended in the 'sludge', the chickens will eat most of it. There must be a place in the shade next to the house or create an area covered with shade cloth.