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Eggs of various animals (mainly birds) Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (known as laying or spawning ) in metabolically independent incubation organs known as eggs , which nurture the embryo into moving offsprings known as hatchlings with little or no embryonic development within the ...
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.
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. There are numerous cultural references to chickens in folklore, religion, and literature.
Older hens gradually produce fewer eggs, and the eggs are usually larger. [1] Since the average lifespan of a pet layer hen is 8–15 years, [2] henopause has received attention as a potential problem for backyard or urban chicken farmers who are eventually faced with the decision to either slaughter older layers or keep them as non-producing pets.
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.
Most fish species spawn eggs that are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina.
Forced molting typically involves the removal of food and/or water from poultry for an extended period of time to reinvigorate egg-laying. Forced molting, sometimes known as induced molting, is the practice by some poultry industries of artificially provoking a flock to molt simultaneously, typically by withdrawing food for 7–14 days and sometimes also withdrawing water for an extended period.
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 ...