Anal prolapse, rectal prolapse and Procidentia in Horses

Image of Prolapsed Rectum on a Mule

This article was written at the suggestion of my friend, Colleen.

Prolapse literally means "to fall out of place." In medicine, prolapse is a condition where organs, such as the uterus, fall down or slip out of place. It is used for organs protruding through the vagina or the rectum or for the misalignment of the valves of the heart. A spinal disc herniation is also sometimes called "disc prolapse." Relating to the uterus, prolapse condition results in an inferior extension of the organ into the vagina, causing weakened muscles.

In the horse, procidentia is a natural occurrence at the time of each bowel movement. What is procidentia? Procidentia is a condition in which the rectum literally turns "inside out" and then returns to its natural state unless there is a rectal prolapse. Rectal prolapse is a condition in which part of the wall or the entire wall of the rectum falls out of place. In some cases, the rectum may stick out of the body (protrusion). Rectal prolapse occurring in horses and mules would be better termed anal prolapse, as it only involves mucous membrane moving posteriorly to form a circular protrusion outside the anus. The condition is not painful. In mares after parturition, it is described as a 10 to 60 mm mucous protrusion.

In young mules and foals, anal prolapse occurs with a frequency similar to that of Gasterophilus haemorrhoidalis. In extensive breeding conditions, the disease is only recognized after some days, leading to intense edema of prolapsed tissues and necrosis of the mucous membrane.

Early cases should be treated with the application of hygroscopic substances like powdered sugar followed by purse-string suturing. When prolapsed tissues are edematous and necrotic, amputation is performed. The prognosis is fair as the removes tissues do not contain any important organs or large blood vessels.

There are multiple causes of rectal prolapse. Straining to have bowel movements, stresses involved in birthing, weakening of the anal sphincter muscle, and/or weakening of the tendons that support the rectum are frequent causes, trauma to that area, congenital problems, genetic susceptibility, infections, any condition that chronically increases the amount of pressure within the abdomen such as COPD/Heaves or obesity. Neurological problems, such as spinal cord transaction or a spinal cord disease, can also lead to prolapse. In rare cases there may be a genetic predisposition. In most cases, though, no single cause can be identified.

• Leakage of stool
• The passage of small amounts of stool
• Bleeding, itching and irritation
• Tissue that protrudes from the rectum

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