Atresia Ani in Horses

Atresia Ani in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

Most common symptoms

Pain / Swelling


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Most common symptoms

Pain / Swelling

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Atresia Ani in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

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What is Atresia Ani?

If your horse has any type of atresia ani, he will be in obvious pain within 12 hours due to the fact that it cannot defecate. Body waste will build up in the intestine until it ruptures if it is not treated right away. Any of these types are serious and must be treated by a veterinary professional who specializes in horses. Surgery is needed to create the anal opening and connect the rectum to where it belongs, but there are many complications. Some of these complications are colonic atony, recurring cystitis (urinary tract infection), anal stricture (narrowing of the anal canal), persisting megacolon (severe constipation and inflammation of the colon), and fecal incontinence (inability to control fecal matter).

Atresia ani in horses is an uncommon congenital defect in which the anus and rectum are not formed properly. The word atresia means absence of a natural opening and ani means anus, which is where it got the name atresia ani. This condition is a birth defect causing serious colic and retention of feces because there is no anal opening for the horse to defecate from. Veterinary experts describe this as the hindgut failing to connect with the perineum correctly to create the rectum and anus. This is a serious and dangerous condition that requires immediate surgery for your horse to survive. There are four types of atresia ani, which are congenital narrowing of the anal canal without a formed opening for the anus, imperforate anus less than 1.5 centimeters from a blind rectal pouch, imperforated anus more than 1.5 centimeters from a blind rectal pouch, and a blind rectal pouch with a normal rectum.

Symptoms of Atresia Ani in Horses

The symptoms of atresia ani may differ due to the four different types. However, the general signs that your horse is suffering from atresia ani are:

  • Swelling of the abdomen that continues to get bigger
  • Abdominal pain that can become excruciating as it progresses
  • Absence of bowel movements
  • Lack of response to enema
  • In females, the feces may come from the vulva (vaginal opening)


  • Type I (membrane atresia) - A membrane or diaphragm blocks the intestinal opening

  • Type II (cord atresia) - The ends are joined by a cord of tissue.
  • Type III (blind end atresia) - An intestinal section is entirely in blind end atresia which leaves two blind ends and a V-shaped intestinal defect.

  • Type IV (multiple atresia) - More than one small bowel atresias of any of the above types

Causes of Atresia Ani in Horses

  • All the types of atresia ani are genetic birth defects
  • The anus and rectum are not formed properly
  • Colic and retention of feces will occur
  • Waste will build up in the intestine until it ruptures
  • This condition causes a need for corrective surgery

Diagnosis of Atresia Ani in Horses

Diagnosing atresia ani in your horse is usually easy for the equine veterinarian to do by palpating the abdomen, which will most likely be extremely swollen due to the fecal backup. However, diagnosing this defect is just the first step. Your veterinarian will also have to determine which type of atresia ani your horse has so a treatment plan can be made. You should bring your pet’s medical and vaccination records if you have any. In most cases, the defect is noticed within the first several days if the defect is completely blocking the rectum from being able to empty. Be prepared to tell the veterinarian exactly what symptoms you noticed that brought you to the decision of seeing a veterinarian.

First, your veterinarian will perform a complete thorough physical examination, which includes body temperature, weight, blood pressure, respiration rate, capillary refill time, a body condition score based on your pet’s body weight, lameness check, and pulse. Also, a quick examination of the skin, teeth, nasal cavity, ears, and eyes will be done. Radiographs (x-rays) with contrast dye and enema can show where the colon ends and any other defects. Abdominal and rectal palpation will be done to help determine the extent of the problem. A laparotomy (surgical incision to diagnose or prepare for a surgical performance) will be done while your horse is under general anesthesia to see exactly what needs to be done and what can be done.


Treatment of Atresia Ani in Horses

Unfortunately, in some cases, there is nothing that can be done to save the horse and euthanasia will be suggested to stop the suffering. You are more than welcome to get a second opinion or to see a specialist that studies atresia ani, but the longer you wait, the longer your horse is in excruciating pain. Some of the treatment plans include:


The first step will be to give your horse an intravenous line with ringer lactate solution and electrolytes to rehydrate your pet. This also makes it easier for the physician to administer medications when needed. Flunixin meglumine may be given for pain.


A midline laparoscopic operation is performed to repair the defect. The details vary depending on the type of atresia ani.

Type I -  The veterinarian will use balloon dilation to expand the anal canal so the fecal matter can pass more easily.

Type II and III -  The veterinarian will have to do at least two operations for these more serious types of defect. The first (colostomy) is done by creating a small opening in the skin and muscles of the abdominal wall. A colostomy bag will be attached for the fecal matter to drain into until the horse is big enough for the second surgery, which is about six months. In the second (and hopefully final) surgery, the veterinarian will move the colon to a different spot and the rectal pouch will be put into place where a new anal opening will be made.

Type IV -  With this serious type of atresia ani, the abdomen will need to be completely opened up to isolate and attach the distal colon and rectum.

Recovery of Atresia Ani in Horses

Horses with type I atresia ani have a good chance of a full recovery and long life. With types II and III, the prognosis really is contingent upon which part of the colon is affected, but the success rate is low so the prognosis is poor. If your horse has type IV, the chances are grave, but possible.

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Atresia Ani Average Cost

From 585 quotes ranging from $3,000 - $15,000

Average Cost


Atresia Ani Questions and Advice from Veterinary Professionals

Atresia Ani Average Cost

From 585 quotes ranging from $3,000 - $15,000

Average Cost