How does a chicken egg become fertilized?

Answer 1

A chicken egg becomes fertilized inside the female chicken's body while she is making the egg. Sperm from the rooster who has mated her in the past couple weeks is stored in her reproductive system and added to her eggs as they are made. Thus fertilization is an internal process.

It's impossible to tell by looking at a chicken egg whether or not it is fertilized. Having a rooster with your backyard hens ensures that virtually all eggs are fertile.

Answer 2

The natural brooding season of chickens, when hens want to sit on, or brood, eggs to incubate them, starts from spring, when the days start getting longer. However, females, called hens, that are around males, called roosters, can lay fertilized eggs year-round. The roosters have reproductive organs known as testes, which produce sperm, which are transferred to the sperm sacs, through tube-like structures called vas deferens. It takes only thirty seconds for the roosters to deposit sperm in the reproductive tract of the hens, called the oviduct. The sperm that leave the body of the rooster through an opening called cloaca, enters the cloaca, then the oviduct, of the female, and travel through the various parts of the reproductive organs (the shell gland of the hen, the isthmus, and magnum) to reach the infundibulum, a funnel-shaped organ. This journey takes almost one week. Once inside the infundibulum, these sperm can remain live for one week or more, waiting for the eggs, which undergo the process of formation.

The eggs are formed as yolk, in the ovaries of the hen. This yolk, when released from the ovaries, travels to the infundibulum. If there are sperm in this funnel-shaped organ, the yolk will get fertilized. Once fertilized, the yolk passes through the same route, through which the sperm traveled to reach the infundibulum. The only difference is that the yolk travels in the reverse direction and completes its structure to form a proper egg, during the course of this journey. The yolk is surrounded by the egg white in the magnum, whereas the formation of the shell membrane starts in the isthmus. From there the yolk travels to the shell gland, where the shell formation is completed and the shell gets hardened. The egg is ready to be laid, which is usually done in the mornings. Once the fertilized egg is laid, the hen is ready to start with the formation of a new egg.

In short, hens can and will lay eggs without a rooster around, but such eggs will be unfertilized and cannot be incubated to develop a chick. You can distinguish a fertilized chicken egg through the method of candling once an egg has been incubated for a few days. During candling, a fertilized egg can be differentiated from an unfertilized one from the presence of veins inside it. It is always better to obtain fresh, fertilized chicken eggs, for the purpose of hatching chicken eggs.