Chicken eggs get fertilized through a process involving mating between a rooster and a hen. Here is how it happens step-by-step:
- During mating, the rooster transfers sperm to the hen via a brief "cloacal kiss," where their cloacas touch and sperm is deposited into the hen's reproductive tract
- The sperm then travel up the hen’s oviduct to specialized sperm storage glands, where they can remain alive and viable for fertilizing eggs for up to about 3 to 4 weeks
- When the hen ovulates, the mature egg yolk is released from the ovary and captured by the infundibulum, the first part of the oviduct. Fertilization occurs here when sperm bind to and penetrate the yolk’s perivitelline membrane near the germinal disc
- Hundreds of sperm may enter the yolk, but only one sperm fertilizes the egg. About 30 sperm near the germinal disc increase the chance of successful fertilization to 95%
- After fertilization, the egg continues through the oviduct where egg white, membranes, and the shell are added over several hours before the hen lays the fertilized egg
- The fertilized egg already contains an embryo that begins cell division within hours and will develop into a chick if incubated properly
In summary, fertilization happens internally in the hen’s oviduct shortly after ovulation, with sperm stored from mating traveling to meet and penetrate the egg yolk before the shell forms
. Hens can lay eggs without fertilization, but a rooster is needed to provide sperm for fertilized eggs that can hatch into chicks
. This process ensures that fertilized chicken eggs contain a developing embryo by the time they are laid.
