Chicken Egg Hatching Cycle

A breakdown of the twenty-one day cycle of a chicken egg, from fertilization to hatching.

| December 2017

How to Speak Chicken (Storey Publishing, 2017) explores tips, tidbits, and scientific facts that are essential for raising your own backyard chickens. Understanding the way chickens sense the world and communicate impending danger, techniques for watching your flock, and insights into how they establish pecking order are all covered by author Melissa Caughey. Additionally she offers insight into chicken body language, intelligence, social interaction, emotion, and problem solving abilities.  

Inner Workings of the Egg

From the time the egg is fertilized, the chick develops rapidly. It takes just 21 days for a chick to grow inside the egg and hatch. The eggshell is made of almost pure calcium carbonate, with more than 17,000 tiny pores to allow air and moisture to pass through. All eggs are coated in a bloom (or cuticle) that helps prevent bacteria and viruses from getting inside the egg. Here is a peek inside this incredible process. 

Day 1: The fertilized egg begins to develop the embryonic disk, where the embryo forms. An air sac in the rounded end adjusts internal egg pressure and air for respiration as the chick grows.

Day 2: The vitelline membrane, which surrounds the vitellus (yolk), begins to form. It allows the albumen (egg white) to pass into the vitellus to nourish the embryo.

Day 3: Blood vessels begin to form, and the head, torso, brain, and beating heart are visible.

Day 4: The amniotic sac begins to develop. 

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