Basic Reproduction Explained
As in all animals, the fusion of the ovum and the sperm is how fertilization occurs. Then an embryo forms and develops into a new organism. The chicken is no exception; their eggs need to be fertilized in order to develop a chick.
A chicken will begin laying eggs between five and six months of age, until then she is called a pullet. However, climate, seasons, and other various factors do play a significant role in laying cycles. Certain breed types are also included in the variances of egg laying, first-time or otherwise. One thing is for sure, when a pullet reaches sexual maturity she will lay eggs whether or not there is a rooster present.
Roosters [males] have reproductive organs which produce sperms that are released during mating. The sperms enter the oviduct of the hen [female] and continue a nearly week-long reproductive journey to meet the eggs. The sperm’s final destination is in the infundibulum. This is where they will wait about a week for the partially formed and unshelled eggs. If there is a yolk, the eggs are fertilized instantly. So, it’s safe to say you can expect fertile eggs seven to ten days after mating.
Note: It is possible the hen may produce fertile eggs the following week as well.
When hens are in the presence of a rooster there is a way to separate the fertilized eggs from infertile by a technique called candling. This method uses a bright light source behind the egg to show details through the shell. Fertilized eggs will show a darker yolk on one end, usually when they are one or two days old. Within two to three days, if incubated, you may actually see indications of a growing embryo.