I had to know what was going on. A pullet starts life with two ovaries, but as she matures, the right ovary remains undeveloped and only the left one becomes fully functional. The functioning ovary contains all the undeveloped yolks, or ova, the pullet started out with. Exactly how many that is depends on which egg-spert you ask. Estimates range from 2, to 4,, or even more. At any rate, from the day she enters this world, each female chick carries with her the beginnings of all the eggs she could possibly lay during her lifetime, but few hens lay more than about 1, of the possible total.
When a pullet reaches laying age, or a hen comes back into lay after a break, one by one the yolks mature, so at any given time her body contains yolks at various stages of development. Approximately every 25 hours, one yolk is mature enough to be released into the funnel of the oviduct, a process called ovulation, which usually occurs within an hour after the previous egg was laid.
If ovulation occurs too rapidly, or if one yolk for some reason moves too slowly through the oviduct and is joined by the next yolk, the pullet will lay an egg with two yolks.
Double yolkers are typically laid by pullets before their production cycle becomes well synchronized, but may also be laid by heavy-breed hens, often as an inherited trait. Sometimes an egg contains more than two yolks; I once cracked open an egg that had three. The greatest number of yolks on record is nine in one egg. When the process is complete, the shell gland at the bottom end of the oviduct pushes the egg into the cloaca, a chamber just inside the vent where the reproductive and excretory tracts meet — which means, yes, a chicken lays eggs and poops out of the same opening.
But not at the same time. This everted, or prolapsed, tissue presses against the intestinal opening to ensure it remains shut while the egg passes through the cloaca. So the egg — having been surrounded by protective uterus tissue — emerges clean. The hen breeds used in commercial egg farming start laying eggs at around weeks four months old. The first eggs laid by hens at this young age are relatively small at about grams.
But over a period of about three months, the egg size increases to an average of 60 grams. Commercial laying hens continue to produce first quality eggs until they are about one and a half years old. After this, their eggs become fewer and shell quality decreases which leads to more cracking and breaking. A hen requires around hours to produce an egg and after it is laid, the process starts all over again about 30 minutes later.
The only reason to have roosters included among a flock of hens would be to produce fertilised eggs as part of breeding programs. This process happens in specialist hatcheries, not on egg farms.
Birds are unique among animals because only one ovary the left matures to the stage where it releases eggs. When a yolk is ready, it moves out of the ovary and into the oviduct - a tube-like structure that is divided into different sections.
Over four hours, the yolk moves through an area of the oviduct called the magnum where egg white protein is added to it. There are many different proteins that make up the egg white. The different protein layers provide protection for the yolk and create a template for the formation of the shell membrane and shell.
After quickly moving through a section called the isthmus where shell membrane fibres are produced, the egg enters the shell gland where the shell forms over about 20 hours. The process is called calcification as layers of calcium carbonate are added to form the shell. During the last two hours of shell formation the bulk of the pigment white or brown is produced and deposited into the outer layers of the shell.
The hen can do this by sitting on the eggs ; this is called "going broody. If fertilized eggs are collected shortly after laying and are kept in a cool place, then the embryo will not mature. Some breeds of chickens are more likely to go broody than others.
In addition, if one hen becomes broody, the other hens around her may also become broody. If you want to know whether or not a freshly laid egg is fertilized, this may be accomplished through a process called candling. Hold the egg is held up against a bright light, and examine the contents for shape and opacity.
You may be able to see the early stages of the embryo and sometimes blood spots as well. However, it typically takes a trained eye to see the differences between fertilized and unfertilized eggs at this stage. Actively scan device characteristics for identification. Use precise geolocation data. Select personalised content. Create a personalised content profile.
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