Candling of Eggs. In maintaining a healthy and germ-free environment, eggs must be candled-examined by shining a light through each egg to see if a chick embryo is developing at least once during incubation so that infertile and dead-germ eggs (eggs containing dead embryos) can be identified. Many operators candle chicken eggs on the fourth or fifth day and turkey and waterfowl eggs on the seventh to tenth day. Some operators candle eggs a second time when transferring eggs to the hatching compartment.