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The yolk of a chicken egg Diagram of a fish egg; the yolk is the area which is marked 'C'. Among animals which produce eggs, the yolk (/ ˈ j oʊ k /; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo.
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.
The term also includes waterfowls of the family Anatidae (ducks and geese) but does not include wild birds hunted for food known as game or quarry. Recent genomic studies involving the four extant junglefowl species reveals that the domestication of chicken, the most populous poultry species, occurred around 8,000 years ago in Southeast Asia. [3]
People in Southeast Asia began harvesting chicken eggs for food by 1500 BCE. [2] Eggs of other birds, such as ducks and ostriches, are eaten regularly but much less commonly than those of chickens. People may also eat the eggs of reptiles, amphibians, and fish. Fish eggs consumed as food are known as roe or caviar.
A commercial chicken house with open sides raising broiler pullets for meat. Chickens farmed primarily for eggs are called layer hens. 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]
A dual-purpose chicken is a type of chicken that may be used in the production of both eggs and meat. [42] In the past, many chicken breeds were selected for both functions. However, since the advent of laying and meat hybrids, industrial chicken breeding has made a sharp distinction between chickens with either function, [ 43 ] so that certain ...
There are still huge hurdles — how to scale up manufacturing and pare back costs, experts say, and the lingering question of whether chicken without the bird is, in fact, chicken — but if you ...
Eggshell membrane is the clear film lining the chicken eggshell displayed. Eggshell membrane or shell membrane is the clear film lining eggshells, visible when one peels a boiled bird egg. Chicken eggshell membranes are used as a dietary supplement. Eggshell membrane is derived commercially from the eggshells of industrial processors.