Some many deal with the issue of internal laying. I don't know a great deal about it since not many vets treat chickens and share their knowledge. There are a few different issues with the reproductive tract causing similar symptoms. Below are some excerpts from The Merck Veterinary Manual defining some of the terms used:
Internal Layer (Poultry)
In these hens, partially or fully formed eggs are found in the abdominal cavity. Such eggs reach the cavity by reverse peristalsis of the oviduct. If they have no shell, they are often misshapen because of partial or complete absorption of the contents. Frequently, only empty shell membranes are present. No control or treatment is known. This condition is related to erratic ovulation and defective egg syndrome (see
Defective or Abnormal Eggs in Poultry).
False Layer (Poultry)
These hens ovulate normally, but the yolk is dropped into the abdominal cavity rather than being collected by the oviduct because of inflammation and resulting obstruction of the oviduct after infection with
Escherichia coli or
Mycoplasma gallisepticum. The yolk is absorbed from the abdominal cavity. The hen looks like a normal layer but does not produce eggs. Hypoplasia of the ovary and oviduct has been associated with infectious bronchitis virus infections (see
Infectious Bronchitis) at an early age (1–2 wk). Atresia or even atrophy of the ovary are caused by severe stress, chronic infections, insufficient feed intake, inadequate feeder space, and feed refusal due to mycotoxins in the feed.
Egg Peritonitis in Poultry
Egg peritonitis is characterized by fibrin or albumen-like material with a cooked appearance among the abdominal viscera. It is a common cause of sporadic death in layers or breeder hens, but in some flocks may become the major cause of death before or after reaching peak production and give the appearance of a contagious disease. It is diagnosed at necropsy. Peritonitis follows reverse movement of albumen and
Escherichia coli bacteria from the oviduct into the abdomen. If the incidence is high, culture should be done to differentiate between
Pasteurella (fowl cholera) or
Salmonella infection. Antibiotic treatment of peritonitis caused by
E coli infections is usually ineffective. Management of body weight and uniformity, reproductive development (ovary follicle growth and maturation), and drinking water sanitation are the best preventive strategies.
When hens have too many large ovarian follicles, a problem described as erratic oviposition and defective egg syndrome (EODES) is seen in broiler breeders. This condition is accompanied by a high incidence of double-yolked eggs, prolapses of the oviduct, internal ovulation, and/or internal laying that often results in egg peritonitis and mortality. EODES is prevented by avoiding light stimulation of underweight pullets too early and by following guidelines for body weight and uniformity, and lighting recommendations for each breeder strain. Overweight hens may also have a higher incidence of erratic ovulations and mortality associated with egg peritonitis.