What causes double yolk eggs?
Double yolk eggs
Female chickens are born with fully formed ovary containing several thousand tiny ova, which form in a cluster like grapes. A follicle- stimulating hormone in the bloodstream develops these ova, which will eventually become egg yolks.
When the ova are ripe, the follicle ruptures and an ovum is released. Usually, when a chicken ovulates, one yolk at a time is released and travels down the oviduct, where it will acquire a surrounding white membrane and shell.
Occasionally two yolks are released at the same time. Double yolk eggs are no more planned than human twins. But some chickens are more likely to lay double yolk eggs. Very young and very old chickens are most likely to lay double yolks; young ones because they don’t have their laying cycle synchronised, and old ones because, generally speaking, the older the chicken the larger the egg she will lay. And for some reason, larger eggs are most subject to double yolks.
If chicken is startled during egg formation, small blood vessels in the wall may rupture, producing in the yolk blood spots – tiny flecks of blood. These eggs are perfectly safe to eat.