An early reference to battery cages appears in Milton Arndt's 1931 book, "Battery Brooding", where he reports that his cage flock was healthier and had higher egg production than his conventional flock. At this early date, battery cages already had the sloped floor that allowed eggs to roll to the front of the cage, where they were easily collected by the farmer and out of the hens' reach. Arndt also mentions the use of conveyor belts under the cages to remove manure, which provides better air control quality and reduces fly breeding.