Chicken Egg Hatching Cycle

Check-out this breakdown of the twenty-one-day cycle of a chicken egg covering development post-fertilization to hatching.

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by Unsplash/Michael Anfang

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.

Day 5: The eye is visible, and the head curls toward the tail. Toes are forming.

Day 6: The upper limbs grow. The vitelline membrane now encases half of the yolk.

Day 7: The beak begins to form.

Day 8: Eye color is discernible. The wings, legs, and beak are forming. The ear canals open, and the brain is set in place in the skull.

Day 9: Toenails and feathers begin to grow.

Day 10: The egg tooth appears and more feathers begin to emerge. The nostrils are visible and the eyelids have grown.

Day 11: The embryo clearly resembles a chick.

Day 12: The chick can hear noises from outside.

Day 13: Leg scales develop.

Day 14: Fluffy down covers the entire body.

Day 15: The yolk is shrinking rapidly. The chick’s head tucks under the right wing to prepare for hatching.

Day 16: The albumen is almost completely consumed.

Day 17: The beak moves into the air space. The kidneys begin to function.

Day 18: Remaining fluids are absorbed.

Day 19: The beak is against the shell ready to pip, or pierce the shell.

Day 20: The yolk is fully absorbed and the umbilicus closes. The chick begins to pip.

Day 21: The chick pecks around the entire circumference of the egg with its egg tooth and breaks through the shell, typically taking 12 to 18 hours with naps along the way.

More from How to Speak Chicken:

Chicken Flock Positions

Excerpted from How to Speak Chicken, © by Melissa Caughey, used with permission from Storey Publishing, 2017.