Double-yolk

Vitellogenesis

Double-yolk eggs occur when ovulation occurs too rapidly, or when one yolk becomes joined with another yolk. These eggs may be the result of a young hen’s reproductive cycle not yet being synchronized. Some hybrid breeds of hens also produce double-yolk eggs by default. Such eggs are produced in India. Heavier poultry breeds such as the buff Orpington have been known to lay triple yolk eggs in their lifetime. Although heredity causes some hens to have a higher propensity to lay double-yolked eggs, they occur more frequently as occasional abnormalities in young hens beginning to lay. Double-yolked eggs usually only lead to observed successful hatchlings under human intervention, as the chickens interfere with each other’s hatching process and die.

Eggs without yolk are called ‘dwarf’ or ‘wind’ eggs. Such an egg is most often a pullet’s first effort, produced before her laying mechanism is fully ready. In a mature hen, a wind egg is unlikely, but can occur if a bit of reproductive tissue breaks away, stimulating the egg producing glands to treat it like a yolk and wrap it in albumen, membranes and a shell as it travels through the egg tube. An archaic term for a no yolk egg is a ‘cock’ egg. Since they contained no yolk and therefore can’t hatch, it was traditionally believed that these eggs were laid by roosters.

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