What is Colic?

Colic is responsible for 1 in 3 emergency equine veterinary call-outs and is a major cause of death or euthanasia in horses. Here at Newnham Court Equine, we have teamed up with the University of Nottingham and The British Horse Society to bring you a series of informative articles about this important condition. Topics covered include:

  • What is colic?
  • Types of colic
  • Recognising colic
  • Colic: Causes and prevention
  • Colic: What to do
  • Colic: What will happen when the vet comes
  • Critical colic cases
  • Colic: The decision to refer
  • Colic: Costs and insurance cover

In this article, we talk about what colic is and how the horse’s digestive system works. Understanding the structure and function of this system is useful in understanding how to prevent colic.

What is colic?

Photo of a horse with the abdomen area surrounded by a dotted line

Figure 1. The dotted line marks the outer margins of the abdomen

The word ‘colic’ simply means ‘pain in the abdomen (belly)’. So although we tend to think of colic as a single condition, there are actually lots of different types of colic.

The horse’s abdomen – which is where colic occurs – is the area enclosed by the blue dotted line in Figure 1. The abdomen contains almost all the organs associated with digestion (stomach, intestines, etc.) as well as a number of others. Disease of any of the organs in the abdomen can lead to colic. However, generally, colic is caused by pain in some part of the digestive system and this series of articles concentrates solely on colic associated with this system.

Structure and function of the equine digestive system

Diagram of the equine digestive system showing stomach, small intestine, small colon, large colon and caecum

Figure 2. The equine digestive system

The major function of any animal’s digestive system is to extract nutrients from the food that is eaten. Horses have evolved to eat grass and have developed a highly specialised digestive system that allows them to break down plant material and use the products for energy. Figures 2, 3 and 4 show the parts of the equine digestive system that are in the abdomen.

Diagram of the equine digestive system in position, righthand side

Figure 3. The equine digestive system in position

Once food has been swallowed, it travels down the oesophagus to the stomach. The food then moves to the small intestine before entering the parts of the intestine that are specialised for digestion of plants: the caecum and large colon. Once digestion has been completed, what is left of the food is expelled via the small colon, rectum and anus.

Diagram of the equine digestive system in position, lefthand side

Figure 4. The equine digestive system in position

The tables below give information about each part of the digestive system, along with some colic-related facts.

Stomach Colic-related facts
• Starts digestion of non-fibrous food
• Relatively small (8–15 litres/1.8–3.3
• Cannot hold large amounts of food
• Unable to vomit • May rupture if contents swell (e.g., unsoaked sugar beet) or if small intestine is blocked because it has twisted or moved into an abnormal position (displacement) causing fluid to back up into stomach
• Secretes acid continuously • Susceptible to ulcers
Small intestine
• Completes digestion of non-fibrous food, including starch and sugars (unless starch/sugar content of diet is excessive) • Excessive starch/sugar may pass to the caecum and large colon without being digested
• ~22 metres (72 feet) long*
• Long tube that hangs off the bottom of a sheet of membrane, a bit like a large, mobile Cumberland sausage hanging off the bottom of a net curtain that is bunched together at the top • Can move within the abdomen
• May twist or move (displace) to an abnormal position
• Secretes ~100 litres (22 gallons) of fluid per
day (most of which is reabsorbed)
• Requires constant, plentiful supply of fluid – hence horse needs constant access to fresh water
• Feed material moves fairly rapidly (~5
hours for stomach and small intestine
• Blockage or obstruction of the small intestine can rapidly lead to problems