Cystic right oviduct is a reproductive disease affecting mainly older laying hens. It is caused by the incomplete regression of the what would be, normally nonfunctional right oviduct. It can also be the result of an underlying illness such as infectious bronchitis virus.
Cystic right oviducts range in size from small 2 cm diameter, elongated cysts to a large fluid-filled sac up to 10 cm in diameter and greater. When cysts grow large, they compress the abdominal viscera and can result in the appearance of a disproportionally enlarged abdomen.
Certain breeds and strains (usually inbred) of egg laying hens are more susceptible to developing cystic right oviduct, such as the Rhode Island Red, White Plymouth Rock, Black Australorp, and Fayoumi.