Written by: Dr. Jacquie Jacob, University of Kentucky
The reproductive tract of a hen is made up of two parts: the ovary and the oviduct (see the article "Avian Reproductive System—Female" for more information about the organs of the reproductive system). The ovary is where the egg yolks develop. The completed yolks are released and picked up by the oviduct for the development of the rest of the egg. If the yolk is not picked up by the oviduct, it is shed into the hen's body cavity. This phenomenon is referred to as "internal laying," and typically such yolks are absorbed by the body. But when internal laying occurs too frequently, the body cavity becomes overloaded with yolk. The hen is then said to be egg-bound and displays a distended abdomen. There is no treatment for this condition and it may be necessary to euthanize the affected hen.