If you have a flock with both hens and roosters, you may be wondering if the hens eggs are being properly fertilized by the rooster. The easiest way to find out if eggs are fertilized is by looking at the yolk. Most eggs are laid about 20 hours after being fertilized and are often fertilized by as many as 5-25 sperm.
Start with the albumen, commonly known as the egg whites. Inside the albumen is a part many people already know, the yellow egg yolk. On the yolk, there is a very small white spot called the germinal disc, which is about the size of a pencil eraser. When the egg is unfertilized, the germinal disc makes a solid white dot or cluster of white dots.
When the egg is fertilized, the germinal disc becomes bullseye shaped, known as a blastoderm. The the blastoderm, which forms from the germinal disc, can also be called the blastodisc and consists of a single layer of hollow cells. With its bullseye look, the inner circle is known as the area pellucida while the outer, peripheral ring is known as the area opaca. Over a quick period of time, this area forms into the embryo, which eventually forms into a chick.
