Eggitarians, Do You Know How Chicken Eggs are Fertilized?

How are Chicken Eggs Fertilized?
For chicken eggs to be fertilized, it is essential that the rooster mates with the hen prior to the formation of the egg. Though, the hen does not necessarily require the presence of the rooster at the time of laying the egg.
Chicken Egg Fertilization Process
The males, called roosters, have reproductive organs known as testes, which produce sperms that are transferred to the sperm sacs, through tube-like structures called vas deferens. The sperms are released through the cloaca of the bird, while mating. It takes only thirty seconds for the roosters to deposit sperm in the reproductive tract (called the oviduct) of the hens. The sperms that leave the body of the rooster through an opening called cloaca, enter the oviduct of the female and travel through various parts of the reproductive organs to reach the infundibulum, a funnel-shaped organ. In this journey, which takes almost one week to reach the destination, the sperms pass through the shell gland of the hen, then isthmus and magnum, finally to reach infundibulum. Once inside the infundibulum, these sperms can remain live for one week or more, waiting for the eggs, which are not fully formed and lack shells. If there is a yolk in the infundibulum, fertilization takes place instantly.

The eggs are formed as yolk, in the ovaries of the hen. A healthy young hen produces a single yolk in every 24 to 26 hours. This yolk, when released from the ovaries, travels to the infundibulum. If there are sperms in this funnel-shaped organ, the germinal disc (called blastodisc) in the yolk will get fertilized to form the embryo (called blastoderm). 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 gets surrounded by the egg white in the magnum, whereas the formation of the shell membrane starts in the isthmus. From there the yolk (covered with egg white) 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 middle of the day. Once the fertilized egg is laid, the hen is ready to start with the formation of a new egg.
Are All Chicken Eggs Fertilized?
A healthy chicken may start laying eggs from the age of four to six months. The egg laying age for chickens may vary with the breed, climatic conditions and various other factors. Even the number of eggs laid by a chicken may vary with all these factors. An average domestic hen may produce around five eggs a week. In between the egg laying periods, these birds take rest. In other words, they do not produce eggs for a small interval, after an egg laying period. Once a chicken starts laying eggs, the productivity is highest during the first year and tends to decline after that.

Now the question is whether all chicken eggs are fertilized? Once the young female chickens (better known as pullets) reach sexual maturity, they will start laying eggs. In other words, chickens that reach the egg laying age will produce eggs, even if there are no roosters. So, mating and fertilization is not necessary for a chicken to produce eggs. In fact, most of the store-bought eggs are not fertilized, as roosters are normally not kept in most of the poultry farms, so as to facilitate mating and fertilization. Only when there is a demand for fertilized chicken eggs, or when they (poultry owners) need a new batch of egg-laying hens, that they search for a rooster. In short, you may not be able to hatch chicks by incubating table eggs, as there is no guarantee that such eggs are fertilized or not.
How Long it Takes to Produce Fertile Chicken Eggs?
One of the common questions with regard to chicken egg fertilization is the time period required for production of fertile eggs, from the date of mating. There are various factors that can affect this time period. In case of a flock with less than ten hens, introducing a sexually active rooster can produce fast results. Once the mating is done, the sperms travel to the infundibulum and this takes almost seven days. So, you can expect fertilized eggs only after seven to ten days of mating. The hen may continue to produce fertilized eggs for the following week. Another factor is the number of hens in the flock. If the flock contains less number of hens, there are higher chances of getting fertilized eggs at the earliest. Even the age of the rooster as well as the hens may play a role in forming fertile eggs. The older they get, the longer you have to wait for fertile eggs.
How to Identify Fertilized Chicken Eggs?
In short, a fertilized egg has an embryo, which is not found in an unfertilized one. A fertilized egg does not mean that it has a chick inside it. It has an embryo (blastoderm - fertilized blastodisc) and this embryo is capable of producing a chick (within 21 days), if incubated in proper conditions. The embryo in a fertilized egg looks like a small flat disc with a ring around it. If refrigerated, fertilized eggs are like the unfertilized ones and do not develop further. Most of the poultry farms have specialized candling equipment for identifying fertile chicken eggs. Candling eggs can be done at home, with a bright LED flashlight.

As the light passes through, unfertilized eggs will show a round yolk, whereas the fertilized ones are found to be opaque. If incubated, within two to three days, fertilized eggs will develop a network of veins and you may also see the growing embryo at this stage (seen with LED flashlight only). You may also crack the egg and search for the fertilized blastodisc or blastoderm. It will be like a small white spot (like a pin point) in unfertilized eggs and in fertile ones, you can find a more pronounced, bigger (around one eighth inch in width) round white spot. The germinal disc should not be confused with the small white string-like structure (chalazae), which is seen in all eggs. Some people believe that eggs with red spots are fertile ones. This is also incorrect, as red spots can develop in any egg, during its formation.
Are Fertilized Chicken Eggs Edible?
This is one of the common doubts about eggs. While some people detest the idea of consuming fertilized eggs, others consider them more nutritious as compared to unfertilized ones. The fact is that fertilized eggs are same as unfertilized ones in taste, appearance as well as texture. It does not develop a chick without incubation. Apart from that, most of the store-bought chicken eggs are found to be unfertilized.
Now, you know how to identify a fertilized chicken egg. If you want such eggs for hatching, get fresh fertilized chicken eggs. Fresh eggs are preferred for consumption too. Both fertilized and non fertilized chicken eggs can be used for this purpose.