AA hernia is defined as a "protrusion of an organ or tissue through an abnormal opening." The common hernias affecting the horse involve the herniation of intestine and are inguinal, scrotal, or umbilical in location. The inguinal hernia is created when a piece of intestine slips down the area adjacent to the inguinal canal (the passage, just under the pelvis, that the stalk of the testicles travels from the abdomen to the scrotum) and dissects into the tissue between the hindlegs. The scrotal hernia is formed when the intestine slips down the inguinal canal and goes directly down into the scrotum (the sack of skin that houses the testicles). The umbilical hernia occurs when a piece of intestine protrudes down into a body wall defect in the umbilicus (the navel area).

The development of an inguinal or scrotal hernia is a crisis when the animal shows signs of colic related to the pain of the compressed and obstructed intestine. With an umbilical hernia, there might be no clinical signs because the intestine that is protruding might not be obstructed.

The umbilicus is the lifeline of the developing animal, connecting it to the outside world (and its mother). The umbilical cord contains a vein, two arteries, and the urachus (a tube-like structure that connects to the foal’s bladder and empties the bladder into the amnionic sac). The arteries and vein bring blood to or from the placenta. Upon entering the body, the vein goes forward and connects to the foal’s blood system via the liver, and the two arteries go up and around the bladder and connect to the foal’s blood system