Hernias in horses: what you need to know *H&H VIP*

A hernia is defined as the protrusion of an organ or tissue through an abnormal opening or weak spot in the surrounding muscle or connective tissue.

Hernias typically occur in the abdomen, where a piece of intestine or fat escapes from inside the abdominal cavity and comes to lie under the skin. Aside from hernias associated with incision closure from previous surgery, the most common naturally occurring types are umbilical and inguinal (groin) (pictured top) hernias.

Other internal possibilities include herniation of intestine into the epiploic foramen, a natural opening adjacent to the liver, or a diaphragmatic hernia, where abdominal structures push through into the thoracic (chest) cavity.

Tummy trouble

The umbilicus (belly button) is the lifeline of the developing foetus, connecting the growing foal and its circulatory system to its mother.

The abdominal wall surrounding the umbilicus is one of the last areas to close during the foal’s development.

Any defect in the closure of the body wall in this location will result in a hernia. Foals can be born with an umbilical hernia, or one can develop during the first few weeks of life.

In most very young foals it is possible to feel a small defect, measuring less than the tip of your little finger, which usually disappears as the umbilicus heals. A larger hole or a small hole that fails to close becomes a hernia, which can be variable in size (generally between one and four fingers’ width).

Umbilical infection and abscessation can also result in an umbilical hernia, in addition to causing severe systemic illness.

From the outside, a hernia appears as a skin sac in the midline of the underbelly. It consists of subcutaneous tissue, fat and possibly intestines. Normally, the hernia is soft and painless, and its contents can be easily pushed back up into the abdomen.

The risk with any hernia is that intestine may get stuck in the opening and start to swell. The blood supply to the trapped intestine can then be cut off, which causes the segment to die through strangulation. Obstruction of the intestine and acute colic can follow.

A strangulated hernia will be tense and painful to the touch and cannot be “reduced” by squeezing its contents back into the abdomen. This is an emergency situation requiring prompt surgical treatment.

Is treatment necessary?

Although small hernias (one or two fingers’ width) are unsightly, they don’t tend to cause significant problems and often resolve on their own within the first year.

It’s sensible to push the contents back into the abdomen daily with your fingers. This allows you to check that the hernia can be reduced and prevents the intestines from “sticking” within the sac.

Surgical repair should be considered for a large hernia, one that does not close on its own, if the intestine within the sac cannot be reduced or if there is any evidence of umbilical infection or abscess.

Ultrasound examination can be useful to evaluate the umbilical area for abnormalities. The umbilicus can look normal on the outside, even if there is infection or an abscess underneath. If this is the case, the hernia can be surgically repaired at the same time that the umbilical abnormalities are removed.

Another form of treatment involves clamping the skin and the edges of the defect over the umbilical hernia using a lamb elastrator ring. This causes tissue scarring and closure of the defect without surgical intervention and can be successful with small hernias.

Great care must be taken not to trap any intestine within the clamp. There is also a risk of infection in the skin as it dies. For these reasons, plus the fact that small hernias usually close on their own, many vets do not recommend this treatment.

One for the boys

There are two types of inguinal hernia: the “true” type and the “rupture”. Both involve the inguinal canal — the tube that passes from the abdomen to the scrotum, through which the testicles descend.

In the true inguinal hernia, a piece of intestine slips down the inguinal canal and into the scrotum. In the inguinal rupture, a segment of intestine pokes through a tear in the canal lining and dissects into the tissues between the hindlegs or into the scrotum.

Congenital inguinal hernias in foals are sometimes called scrotal hernias. These are usually found shortly after birth and tend to resolve spontaneously within three to six months, rarely resulting in intestinal strangulation.

Reduction of the hernia should be carried out daily by hand, or by applying a bandage truss. Surgical correction may be necessary if the hernia does not resolve spontaneously or enlarges.

Inguinal rupture, although less common in young foals, usually occurs within 48 hours of birth and requires immediate surgical management. Colic, depression and swelling of the prepuce and scrotum may be present, while the scrotal skin may be bruised, cold and moist.

In mature horses, inguinal hernias are more common than ruptures.

Most cases are unilateral (on one side only) and occur after strenuous activity that results in increased intra-abdominal pressure, such as covering a mare.

Inguinal hernias and ruptures have been reported in a wide range of ages and breeds of entire males. Standardbreds, draught breeds, warmbloods, Andalusians and Tennessee walking horses are particularly at risk. They rarely occur in geldings, probably because the inguinal canal reduces in size soon after castration.

Emergency surgery

In either case (hernia or rupture), intestine stuck in the scrotum may swell and strangulate — resulting in severe colic that requires urgent surgical treatment. The scrotum on the affected side is usually firm, enlarged and painful on palpation.

Ultrasound examination can be useful to identify trapped intestine. Non-surgical reduction of the hernia may be performed by external compression under general anaesthesia, but this is not always successful.

Castration is usually required at the time of surgical correction, although testicle-sparing techniques and subsequent procedures aimed at preventing recurrence of the hernia have been developed in the last few years and are available at some hospitals.

Inguinal herniation can occur following castration, when it is usually termed “evisceration”. This most frequently happens within 24 hours of castration, but has been reported to occur up to 12 days later.

Evisceration is frequently fatal.

A closed castration technique, where the inguinal canal lining is ligated (tied) during surgery, is often recommended for at-risk breeds, especially in mature stallions, or in animals with a prior history of scrotal or inguinal herniation as foals.

Ref: Horse & Hound; 30 June 2016