How Do Roosters Fertilize Eggs?

by Abbas Jahangir · Published January 19, 2025 · Updated January 20, 2025

A hen does not need a rooster to lay eggs. However, if the intention is for these eggs to be fertilized, that is, to produce chicks, then the presence of a rooster is necessary to provide sperm.

If the hen is not around any rooster, she will lay eggs but will not have chicks. In order for her to reproduce, her eggs must absolutely be fertilized. It is the law of nature. A mating between a rooster and a hen is therefore essential.

How Do Roosters Fertilize Eggs?

If the hen is not around any rooster, Hens will lay eggs but will not have chicks.

To copulate, the two chickens practice “cloacal kissing”.

First of all, a rooster does not impregnate a hen. Hens do not get pregnant, they lay eggs which may or may not be fertile.

Eggs are fertilized when a rooster mates with a hen. This is not sex as we think of it, with one sex organ penetrating another. Like most bird species, roosters do not have penises and hens do not have vaginas, as in mammals. Both sexes have an opening called a cloaca, which is used for reproduction and excrement. Eggs are also laid through the cloaca.

When a rooster begins mating, he circles the hen, lowering one wing during courtship. In an ideal world, the hen would crouch down and flatten her back for him and remain still. Holding her head feathers for balance, he would mount her. The rooster’s tail would be raised and the hen’s tail would be lowered so that their respective cloacas could make contact. This is called the “cloacal kiss.”

The sperm thus passes from the rooster to the hen. The whole process takes only a few seconds. If the hen has not squatted for the rooster, he will often grab her and mate her anyway. A rooster can mate with a hen several times a day.

Once the sperm is in the hen’s body, it is retained in the oviduct, the egg-expelling tube in animals . When the egg yolk leaves the ovary and enters the oviduct, the sperm unites with the egg and fertilization occurs . The sperm remains viable inside the hen’s body for up to three weeks, and a hen can lay fertilized eggs during these three weeks without further mating. A hen can also store sperm from more than one rooster.

The egg will then only develop when certain conditions are met. The most important of these conditions is that the egg be at about 37 degrees Celsius (about 99 degrees Fahrenheit) for more than twenty-four hours.

Tips and How Chicken Breeding Works

To successfully raise chicks, it is important to take into account the very specific way in which chickens reproduce.

Breeding chickens to obtain chicks is not something that can be improvised. Here is some information related to how reproduction works in chickens that will guide you:

The best season for reproduction is in April and May. Be aware that light greatly influences and stimulates mating between male and female.
For light breeds, 1 rooster can be used to fertilize 10 hens. For heavy breeds, 1 rooster is used to fertilize 6 hens.
In a mating, all the eggs are fertilized at the same time. It is therefore considered that all the eggs laid 10 days after mating are suitable for producing chicks and can therefore be incubated. However, a good fertility rate is observed which can be reached 4 days after the introduction of the rooster to the hens.
The hen has such a sperm storage capacity that she is able to lay fertilized eggs up to 3 weeks after the rooster is removed from the group of hens.
Once the eggs are fertilized, you have the choice between:

The natural method of brooding (the hen broods her eggs) if your hen is a good broody hen. This method is the least expensive, but it generally produces a smaller number of chicks.
The artificial method of the chick incubator. In this case, you will place the eggs in the device as soon as they are laid.

Copulation

Before mating, the rooster performs a grand courtship display. Then the hen crouches down and accepts the male who mounts her. The rooster is said to “coach the hen”.

There is no penetration between the two protagonists. Mating consists of joining the two cloacas of the rooster and the hen. The rooster then deposits his sperm at the entrance of the hen’s cloaca. The sperm then travel for 24 hours in the hen’s reproductive tract and end their journey in the reproductive cell called an ovum.

Good to know: a single rooster in the farmyard not only allows the fertilization of several eggs at once in the same hen, but also the fertilization of several hens.

Internal fertilization

Once copulation has occurred, here are the steps of internal fertilization:

Fertilization between a male reproductive cell and the female reproductive cell that produces the egg cell.
Next comes the embryo which will be protected by a shell.
The egg forms, descends into the oviduct to be laid.
The hen or incubator incubates the egg for the necessary time (21 days), then the chick hatches by breaking through the shell.

How do you know if an egg is fertilized?

A close look will tell you if a chicken egg is fertilized. When you’ve eaten fried eggs, you may have noticed a small dot on the yolk. This is the cell in which the embryo is developing. If fertilization occurs, the embryo feeds on the yolk to ensure its development. The latter is visible through the shell. Go to a dark room and place a bright light source, such as a flashlight or smartphone torch, under the most rounded side of the egg. Depending on the maturity of the fetus, here’s what you’ll see in fertilized eggs:

If you see veins marking the inside of the egg, it is fertilized and has been laid for a short time,
If you see a black shape, of varying size depending on the stage of development, it means that there is a chick inside. When the end of incubation approaches, it is possible to distinguish the outlines of the chick’s body and head.

An unfertilized or newly laid egg is completely transparent. However, you can sometimes see a few tiny black dots.

What do you do with fertilized eggs?

It is quite possible to eat them. You have understood that a fertilized egg is not an egg that contains a formed chick. It takes the time of incubation, that is 21 days, for the embryo to develop.

To have chicks, once the eggs are fertilized, there are two methods available to ensure the development of the embryo:

or you appeal to the brooding instinct of your hens. Be careful because this instinct varies greatly from one breed to another, some hens are very poor at this exercise, which risks compromising your plans to see eggs hatch and chicks born. The method is certainly less expensive, but it is also the most random;
either you purchase an incubator, also called an incubator. The eggs are placed in the device as quickly as possible after laying.

It is best to sort the eggs before placing them in the incubator. Only those that have a normal size, shape, color and texture should be kept. If any of these parameters are out of the ordinary, such as a pointed egg, with a bump, a porous shell, too thick, cracked, etc., it is best not to place it in incubation.

Depending on the degree of dirt on the surface of the egg, it may be necessary to clean it in order to limit the risk of bacterial infection in the incubator. Eggs can be scrubbed with a toothbrush provided that the action is gentle and light so as not to thin the shell too much. You can also wash an egg in clean water, at a temperature higher than that of the egg, to prevent it from passing through the shell, but this removes the protective cuticle of the egg, making it vulnerable to bacteria. Eggs that are too dirty should be discarded because you will not be able to clean them properly. It is also preferable not to eat them. The ideal is not to have to clean an egg: to do this, monitor the hygiene of the nests by frequently replacing the litter and collecting the eggs daily, if possible as soon as laying is finished. There are fumigation disinfection processes but they are quite delicate to implement and there are great risks of killing the embryo when they are not controlled.

If you are using an incubator, it should be started one day before the eggs arrive to ensure that it is working properly. The recommended humidity for the first 18 days is 50%, then 70% for the last 3. As for the temperature, set it to 37.7°C for the first 18 days and 37.2°C for the last 3. When you receive your eggs, let them sit at room temperature for 12 hours before placing them in the incubator, with the point facing down. An automatic incubator turns the eggs. If yours is not, do this twice a day for the first 18 days. Even if you have sorted your eggs, natural selection completes the exercise: not all incubated eggs will give birth to a chick.