A white leghorn chick emerges from an egg. From the time the eggshell is broken to the time the chick emerges is approximately 22 hours. The chick starts by breaking the eggshell with a sharp part of its bill. After an air hole is created in the egg, the chick will take several hours rest before enlarging the hole. The normal incubation time for a chicken egg is 21 days at 37 degrees C (100F). The eggs must be turned three times a day and kept at the correct humidity level. Leghorns are one of the best-known breeds of chicken. They produce the majority of the world's crop of white eggs.