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The traditional modes of reproduction include oviparity, taken to be the ancestral condition, traditionally where either unfertilised oocytes or fertilised eggs are spawned, and viviparity traditionally including any mechanism where young are born live, or where the development of the young is supported by either parent in or on any part of their body.
Most chickens are raised for food, providing meat and eggs; others are kept as pets [1] or for cockfighting. Chickens are common and widespread domestic animals, with a total population of 26.5 billion as of 2023, and an annual production of more than 50 billion birds. A hen bred for laying can produce over 300 eggs per year.
A common practice among hatcheries for egg-laying hens is the culling of newly hatched male chicks since they do not lay eggs and do not grow fast enough to be profitable for meat. There are plans to more ethically destroy the eggs before the chicks are hatched, using "in-ovo" sex determination.
Hens crave privacy and darkness when laying eggs, so plan for at least one nesting box for every four or five hens. A box that measures 14"W-by-14"H x 12"D will give even a big gal plenty of room.
The only living mammals that lay eggs are echidnas and platypuses. In the latter, the eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). [11] After laying her eggs, the female curls around them.
A yolkless egg is most often a pullet's first egg, produced before her laying mechanism is fully ready. In a mature hen, a yolkless egg is unlikely, but can occur if a bit of reproductive tissue breaks away, stimulating the egg-producing glands to treat it as a yolk and wrap it in albumen, membranes and a shell as it travels through the egg tube.
Eggs without yolks are known as "dwarf" or "wind" eggs, [19] or the archaic term "cock egg". [20] Such an egg is most often a pullet's first effort, produced before her laying mechanism is fully ready. Mature hens rarely lay a yolkless egg, but sometimes a piece of reproductive tissue breaks away and passes down the tube.
Typically large numbers of eggs are laid at one time (an adult female cod can produce 4–6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how ...