Chicken Reproduction – Sperm & Eggs

“Does the rooster have to cover the hen each time a egg is formed for it to be fertile? I understand, and perhaps I misunderstand, that the sperm of the rooster is stored in the hens body until a egg passes by and then it is fertilized? So does a rooster deposit sperm that effects several eggs, or must he make a fresh deposit for each egg? Thanks” ~ Sam

Hi Sam, thanks for the question.

I’m going to take a step backward to the point of ovulation before we get to fertilization because I think it makes fertilization easier to understand.

The hen’s reproductive system is made up of an ovary and an oviduct.

A mature ovary, which looks like a cluster of grapes, may contain up to 4,000 small ova. Each of these ova can develop into a yolk.

About 7-9 days before ovulation, hormones cause an ovum to develop in sequence to a yolk.

On each yolk is a white spot called the germinal disc, this is the true ova. All eggs, whether fertile or not contain this disc. Crack an egg open and see if you can find it.

The rooster covers the hen and holds onto the feathers on the back of her head with his beak while steadying himself on top of her with his feet. She sort of stoops to present herself to him and to endure his weight.

Both the hen and rooster’s sex organ is called the cloaca. It is a dual purpose organ for the purpose of mating as well as excrement.

Often times the cloaca is referred to as the vent. When the cloaca are brought together, the sperm is transferred from the rooster to the hen.

Once a rooster and hen mate, the sperm is held in the oviduct. As the yolk leaves the ovary and enters the oviduct, the sperm joins with the ova (the germinal disc) and fertilization occurs. Cell division begins even while the rest of the egg is still being formed.

Once the egg is laid, it must be held under the right conditions, temperature and humidity, for a chick to fully develop. These conditions are created by a broody hen sitting on the eggs, or within an artificial incubator, for the duration of 21 days.

The rooster deposits enough semen to fertilize many, many eggs. The longevity of the sperm is limited though and one mating only has the potential to fertilize the eggs for 4-5 days.

There is no way to tell if an egg is fertile when it is laid. The only way to determine if fertilization has occurred is to “candle” the egg after at least 4 days of incubation.

It is important for the rooster to have free access to the hens to ensure fertilization if you want to hatch chicks.

You were on the right track Sam and I hope this has been a clarification for you.