English
Inguinal hernias, also referred to as scrotal hernias, occur when a horse’s intestine protrudes through the supporting muscles around the reproductive tract, making a noticeable bulge.
An inguinal rupture occurs where a horse’s intestine slips completely through a tear in the muscle wall, settling on the other side of the musculature that normally protects it. Both conditions can lead to severe complications if left untreated.
Hernias can be present at birth or acquired, often occurring after castration. While relatively rare, inguinal hernias are a significant concern in horses due to the risk of strangulation, where blood flow to the affected area is compromised, causing extreme pain and tissue death.
Recognizing the symptoms, such as scrotal swelling and signs of colic, increases the likelihood of early detection and treatment. Understanding the risk factors, including breed predisposition and recent physical activities, can help in preventing and managing inguinal hernias.
Inguinal Hernias in Horses
Herniation describes any instance where the intestines are able to shift out of the abdominal cavity through the protective muscles around them. Different hernias are categorized according to which part of the body they arise in.
Inguinal or scrotal hernias involve herniation through the ring of tissue that separates the abdomen from the scrotum. [1][2][3][4][5][6][7] In cases of inguinal hernia, the intestine settles either inside or outside the membrane that surrounds the testicles. [1][2]
This condition can be acquired, often after castration of male horses. Some foals are born with a congenital form of the condition which tends to be less severe. [1][2][8]
Whether in adult horses or foals, the condition is most serious when the blood flow to the intestine and the testicles is interrupted, leading to extreme pain and eventually tissue death. [3][7]
Testicular Anatomy in Stallions
To understand what happens during inguinal herniation, it is useful to know the stallion’s key anatomical structures. [1][9]
- Inguinal Canal: A passage in the horse’s lower abdominal wall that allows the spermatic cord to pass from the abdomen into the scrotum. This structure is made up of the vaginal (also known as internal) and external inguinal rings.
- External Inguinal Ring: The outer opening of the inguinal canal located in the groin.
- Vaginal (or Internal Inguinal) Ring: The inner entrance to the inguinal located in the abdominal cavity. The intestine passes through this structure during inguinal herniation. In the case of inguinal rupture, the intestine passes through a tear in the vaginal ring or vaginal tunic.
- Vaginal Tunic: A thin, double layered membrane that surrounds the testicles and spermatic cord. It provides a covering for these structures as they pass through the inguinal canal. In the case of inguinal hernia, the intestine settles inside this membrane. In the case of inguinal rupture, the intestine passes through a tear in this structure or the vaginal ring and settles outside of the vaginal tunic.
- Spermatic Cord: This tube contains the blood vessels, nerves, the vas deferens, and lymphatics necessary to support and direct the actions of the testicles. It passes through the inguinal canal to the testicles. During herniation, pressure put on this structure can interfere with the delivery of blood and oxygen to the testicles, requiring partial or complete castration.
Illustration: Dr. Ana Mesa, PhD
Direct and Indirect Hernias
The terminology used to describe inguinal hernias in humans includes direct and indirect hernias. Many researchers also use these terms to describe hernias in horses. [2][4][5][7]
Researchers describe the difference between the two types of hernias in horses as: [1]
- Inguinal hernia: Used instead of indirect hernia. The most common type of hernia in which the intestine drops through the vaginal ring and settles inside the vaginal tunic.
- Inguinal rupture: Used instead of direct hernia. A hernia where the intestine drops through a hole in the vaginal tunic or the vaginal ring and ends up in the space outside the vaginal tunic.
Symptoms
The main symptom of inguinal hernia in horses is moderate to severe colic. [1][2][7]
Common signs of colic include: [1][10][11][12][13][14]
- Lethargy
- Reduced appetite
- Biting or staring at the flanks
- Restlessness
- Teeth grinding
- Stretching, dog-sitting, crouching, or lying on the back
- Curling the upper lip (Flehmen Response)
- Tensed abdomen
- Kicking at the abdomen
- Lying down
- Rolling
- Decreased stomach noises
- Rapid breathing
- Sweating
- Bloating
- Changes in the color of the gums
- Rapid heartbeat
Physical Signs
Horses with an inguinal hernia may have a swollen prepuce (the skin surrounding the penis). [2]
The scrotum on the affected side is often: [1][2][7]
- Firm
- Cool
- Enlarged
- Painful
In the case of congenital inguinal hernia, scrotal swelling is typically the only symptom. [5]
In the rare case that a foal’s intestine becomes strangulated or experiences congenital inguinal rupture (direct inguinal hernia), additional symptoms may develop, including:[1][2][5]
- Lethargy
- Cold, moist scrotal skin
- Swelling of the prepuce and scrotum
Causes
The causes of inguinal hernia in horses are not completely understood at this time. [7]
Possible explanations for acquired inguinal herniation include: [1][2][7]
- Movement of the intestines in the body during mating or exercise
- Morphological abnormalities in the vaginal ring
- Changes in intra-abdominal pressure during exercise
Some research suggests that genetics may play a role in this condition. [7] This is because some breeds have a higher risk of this condition, in some cases due to larger than average inguinal canals. [2]
For foals born with congenital inguinal hernia, the cause is presumed to be genetic. [5]
Risk Factors
Inguinal herniation occurs mostly in male horses. The condition is extremely rare in females. [1][6] Inguinal hernias are relatively rare in intact male horses. [1]
Scrotal hernias are more common in geldings just after castration. [1][4][8] Most post-castration cases occur within 96 hours following surgery but incidents have been reported up to two weeks post-operation. [1][4]
Inguinal hernias are less common in geldings that have recovered from castration. [2] This is because the vaginal ring reduces in size once the horse is castrated. [1]
Horses with a history inguinal herniation at birth are at greater risk of developing an inguinal herniation later in life. [1]
Breeds reported to have a higher incidence of inguinal hernia include: [1][2][6][7]
- Standardbred
- Tennessee Walking Horse
- European