Atresia Ani

Also Known As

Anal atresia, Blockage (anus)


Atresia ani is a congenital anomaly affecting the anus and anal canal of the foal. An atresia is a blockage that can affect various areas along the intestinal tract. The condition is rare in foals.

Affected animals usually develop signs of colic during the first 24 hours of life. Depending on the location of the atresia, little or no mucus, meconium or feces will be passed by the foal.


  • Absence of anus or rectum
  • Presence of a membranous septum with no external opening or a very small exterior opening
  • Absence or minimal amounts of mucus, meconium, and feces
  • Colic-like symptoms
  • Distended abdomen


Atresia ani is a congenital condition that may be inherited. The condition is rare and little relevant literature is available.


Although no absolute method of prevention is known, careful selection of breeding stock by eliminating mares or stallions that have produced foals with atresia ani may be helpful. Certainly, a veterinarian should be consulted if there are questions relative to the condition.


Treatment of the condition is considered to be possible by some veterinarians if the problem is caused by a simple blockage of the rectum or anus by the cloacal membrane or the presence of a membranous septum. In the case of the absence of the anus and associated structures, surgery becomes very complicated and the success rate in saving the life of the foal is very low.

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