Prolapses from the cloaca can be a serious and often life-threatening condition in birds. These may originate from the cloacal
wall, reproductive tract, or intestine. Cloacal prolapse may occur secondary to chronic straining from masturbation, egg laying,
space-occupying abdominal masses, and inappropriate weaning and social behavior. Prolapsed tissues are at risk of trauma,
desiccation, infection, and ischemia. Affected birds should receive immediate medical attention. Prognosis depends on properly
identifying the prolapsed tissue and initiating appropriate therapy in a timely manner.
Anatomy
The cloaca (Latin for sewer) is the common opening for the urinary, reproductive, and gastrointestinal tract of birds. It is divided into three chambers:
the coprodeum, urodeum, and proctodeum (from proximal to distal, the first letters spell "CUP"). The coprodeum is the chamber
into which the rectum empties. It is the largest chamber of the psittacine cloaca. It has flat, avillous mucosa and extensive
vasculature. It is separated from the second chamber, the urodeum, by an encircling sphincter-like ridge, the coprodeal fold.
This fold can completely close off the coprodeum from the other chambers of the cloaca, preventing contamination of eggs or
semen during egg laying or ejaculation.
The urodeum is the smallest cloacal chamber in psittacines. It receives the ureters, the oviduct (females), and ductus deferens
(males). The ureters enter the urodeum on either side of the dorsal midline. In females, the oviduct has a rosette-like opening
on the left dorsolateral wall. In males the ductus deferens enters the urodeum on symmetrical, raised papillae located on
the left and right dorsolateral walls. It is separated distally from the proctodeum by the uroproctodeal fold. The urodeal
mucosa is smoother and less vascular than that of the coprodeum. The urodeum exhibits retroperistalsis, pushing urates and
urine cranially into the coprodeum and rectum, where water and solutes are further resorbed, thus maximizing water conservation.
The proctodeum is the final cloacal chamber and is slightly larger than the urodeum in most birds. It is the most frequent
site of papillomas in psittacines. It gives rise to the bursa of Fabricus on the dorsal midline, just caudal to the uroproctodeal
fold. The bursa is the site of B-lymphocyte production in young birds. In mature birds the lymphoid tissue involutes, but
the bursal chamber frequently persists and can be viewed during cloacoscopy.
The vent is the final structure of the cloaca. It is the transverse opening in the ventrocaudal body wall, through which body
wastes and reproductive products are expelled. It is comprised of dorsal and ventral lips, and surrounded by voluntary muscles
that form a sphincter.
Clinical presentation
Because of their stoic nature, affected birds often behave normally. Birds with advanced lesions may present depressed, fluffed,
and less vocal. Affected birds may exhibit inappetence, inactivity, or dyspnea signified by tail-bobbing or open-mouth breathing.
There may be scant feces or droppings streaked with blood. Birds may appear to strain, groom excessively, or pick at the vent
region, and there will be an intermittent or persistent mass protruding from the vent. Feathers around the vent will almost
always be soiled with feces or urates. With concurrent Clostridium infection, there may be gas and offensive odor.
Etiology
The proximate cause for cloacal prolapse in most cases is straining and/or loss of normal cloacal sphincter tone. Factors
that potentially lead to cloacal prolapse include poor nutrition, obesity, cloacal papilloma, cloacitis, constipation, diarrhea,
peritonitis, abdominal mass, abnormal egg, chronic egg laying, and behavioral abnormalities.
