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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.
The first amniote egg – that is, a hard-shelled egg that could be laid on land, rather than remaining in water like the eggs of fish or amphibians – appeared around 312 million years ago. [6] In contrast, chickens are domesticated descendants of red junglefowl and probably arose little more than eight thousand years ago, at most. [7]
The UK alone consumes more than 34 million eggs per day. [84] Hens of some breeds can produce over 300 eggs per year; the highest authenticated rate of egg laying is 371 eggs in 364 days. [85] After 12 months of laying, the commercial hen's egg-laying ability declines to the point where the flock is commercially unviable.
As male birds of the laying strain do not lay eggs and are not suitable for meat production, they generally are killed soon after they hatch. [121] Free-range eggs are considered by some advocates to be an acceptable substitute to factory-farmed eggs. Free-range laying hens are given outdoor access instead of being contained in crowded cages ...
Male chicks on a macerator conveyor belt, seconds before they are killed Chicks ground by a macerator. Chick culling or unwanted chick killing is the process of separating and killing unwanted (male and unhealthy female) chicks for which the intensive animal farming industry has no use.
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 ...
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.