i've been thinking a lot about eggs lately. my friend catherine just brought some from her farm to the city. she gave francine and i each two dozen. francine and i were trying to remember how an egg was made. catherine cautioned us that she had not washed the eggs, and we were wondering why that was important.
here's some information from enchanted learning
The Formation of an Egg:
Cross Section of a Newly Laid Egg
The Yolk: The chicken egg starts as an egg yolk inside a hen. A yolk (called an oocyte at this point) is produced by the hen's ovary in a process called ovulation.
Fertilization: The yolk is released into the oviduct (a long, spiraling tube in the hen's reproductive system), where it can be fertilized internally (inside the hen) by a sperm.
The Egg White (albumin): The yolk continues down
the oviduct (whether or not it is fertilized) and
is covered with a membrane (called the vitelline membrane), structural fibers, and layers of albumin (the egg white). This part of the oviduct is called the magnus.
The Chalazae: As the egg goes down through the oviduct, it is continually rotating within the spiraling tube. This movement twists the structural fibers (called the chalazae), which form rope-like strands that anchor the yolk in the thick egg white. There are two chalazae anchoring each yolk, on opposite ends of the egg.
The Eggshell: The eggshell is deposited around the egg in the lower part of the oviduct of the hen, just before it is laid. The shell is made of calcite, a crystalline form of calcium carbonate.
This entire trip through the oviduct takes about one day.
Let me begin with the fertilization of eggs in the mating of a rooster with a hen. Birds, like mammals, use internal fertilization. Many species of birds lack a penis; instead, the male just has a genital opening (cloaca), which must be positioned against the female's genital opening (also called a cloaca) for sperm transfer. Male chickens, however, do have a small penis to facilitate mating. In any case, after copulation, which only lasts a few seconds, the sperm quickly swim up the oviduct toward the ovary. The sperm can stay alive in the oviduct for several weeks, ready to fertilize the next egg cell (oocyte) that appears.
Oocytes are produced in the ovary, packaged with yolk within a thin protein membrane, and released one at a time into the funnel-like infundibulum of the oviduct. The oviduct is a tubular passageway leading from the ovary to the outside world. It is also an assembly line in which the various layers of the egg are constructed. After an oocyte-yolk package is released into the infundibulum, it lingers there for about 20 minutes. If sperm are present, then the oocyte is fertilized and becomes an embryo. But if no sperm are around (that is, if the hen has not mated), then the egg still proceeds down the assembly line of the oviduct. In this assembly line, albumen (egg white) is added around the yolk, shell membranes are added, and the shell itself is constructed. Finally, the complete egg is pushed through the vagina and out the cloaca.
If the egg has been fertilized, then the embryo inside has already divided several times but remains a group of unspecialized cells. When the egg is incubated at about 37 to 38 °C, the embryonic cells differentiate to form a chick, which will hatch after 21 days. If the egg has not been fertilized, then the oocyte within will never grow or divide, and the egg will never hatch. The eggs you buy at the supermarket are eggs that have never been fertilized.
Domestic chickens lay one egg every 26 to 28 hours (about one egg a day) for a period of 4 to 6 days. In between periods of egg laying, the hen rests. Wild birds may rest for months before laying more eggs, but domestic hens, specially bred for abundant egg production, may rest for as little as 1 day between egg-laying periods. Note that hens will lay eggs even without mating with a rooster.
Commercially, if the goal is to produce eggs, then hens are kept away from roosters, and eggs are collected as they are laid. If the goal is to produce poultry meat, then hens are mated with roosters, and the eggs are incubated to give rise to chicks. Of course, even a farm that produces only eggs will need to have some matings to replace the hens that grow too old to lay eggs.
I would have put that information behind a cut, but i don't know how to do that on typepad. Anyway, francine was worried that the eggs came out of the rectum, so we're ok on that count. then i was telling my sister that the eggs came out in different colors.
she said that the color of the egg was dependent on the color of the chicken feather. but catherine's eggs are tinged with blue and green and can be polka dotted. So we're thinking her information source was wrong. I haven't seen too many blue chickens.
The Chicken Fact Site says:
Sure enough, the Ameraucana and Araucana can lay eggs colored in shades of green or blue, depending on the breed and it's ancestry.
And wikipedia says:
Egg shell color is caused by pigment deposition during egg formation in the oviduct and can vary according to breed, from the more common white or brown to pink or speckled blue-green. Regarding chicken eggs, the color of the egg depends on the color of the bird. According to the Egg Nutrition Center, hens with white feathers and earlobes will lay white eggs, and chickens with red feathers and earlobes will lay brown eggs.
so my sister is right. the color of the eggs is related to the color of the chicken. but the eggs aren't exactly the color of the chicken.
wikipedia also had this reassuring comment:
Most commercially produced chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without any roosters. Fertile eggs can be purchased and eaten as well, with little nutritional difference. Fertile eggs will not contain a developed embryo, as refrigeration prohibits cellular growth.