A fully formed egg may lodge in the shell gland or vagina because the egg is too big (eg, double-yolked) or because of hypocalcemia Calcium Metabolism Problems in Hens Various problems related to calcium, including hypocalcemia, sudden death, osteoporosis, and cage layer fatigue, have been observed in hens. Pullets or hens with insufficient dietary calcium... read more , calcium tetany, or previous trauma (usually pecking) to the vent or vagina that obstructs oviposition (see ).
This condition may be more prevalent in young hens that are brought into production before body development is adequate or in hens that are overweight or obese. It occurs more often during spring and summer months because of overstimulation of birds by increasing light intensity and day length, which can be compounded by rapid increases in the amount of feed or excessive protein (lysine).
Impacted oviducts are usually recognized only during necropsy in commercial poultry.
When impaction occurs, eggs that continue to form create layers of albumen and yolk material, and the oviduct becomes very large. Some eggs are refluxed to the abdominal coelom (abdominal laying; internal lay Internal Laying in Poultry In internal laying, partially or fully formed eggs are found in the abdominal cavity (see ). Such eggs reach the cavity by reverse peristalsis of the oviduct. If they have no shell, they are... read more ), and affected hens assume a penguin-like posture.