Where do eggs come from?

Here is a bit on the birds and the bees...

During embryonic development, both right and left ovary and oviduct are present. But not all species have functional right sides. Ducks, geese, and guineas are firing on only the left sides.

Eggs start out as ova, a single cell. There are on the order of a couple hundred to thousand of these in the left ovary. The ova mature in order, adding yolk (food source) over time, with the largest being the next to be released and captured by the infundibulum.

There is a small 30-minute window where the ova is released by the ovary and the sperm get a chance to connect. Sperm are stored by the birds in special receptacles that keep the sperm alive for up to 30 days. The window is closed once the ova is captured by the infundibulum and begins the process of layering of the albumen (the whites).

The magnum is the longest part of the oviduct; it is here that the albumen collects. This is about a 3 hour process.

Following the layering of the albumen, the egg passes into the isthmus, where the inner and outer shell membranes are formed. This takes another hour or two.

Finally, the ova passes into the uterus, which is the shell-producing gland. It takes another 18 - 21 hours for the shell to form.

When the egg is laid, it passes through the vagina, where it picks up a cuticle layer, which is a protective coating that helps keep out bacteria. It does a 180 degree rotation here, so that the big end comes out first.

The cloaca is the "common sewer" of the bird. Here is where the digestive, urinary, and reproductive tracks all meet. What you actually see on a bird is called the "vent", the exit itself.

Fascinating fact: eggs from factories are washed to remove any sign of "stain" that commonly occurs when the egg passes through the cloaca. Washed eggs are actually more susceptible to infection because they have lost their protective coating, the cuticle. This is one reason why farm-fresh eggs tend to have a better shelf life. (Though, they do sometimes look nasty!) Store-bought eggs are washed in warm water, often containing soap or other chemicals, then sprayed with a fine mineral oil mist, which helps get back some of that protection it lost during the cleaning process. All of this just for the sake of a nice looking egg.