The 11 systems of the horse – The Digestive System

What is it comprised of?

The digestive system of the horse is made up of the mouth, esophagus, stomach, small intestine and large intestine, which is made up of cecum, large colon, small colon and the rectum.  The whole digestive system of the horse is around 30 metres long, mostly comprised of intestines.

How does the process work?

When a horse eats, it takes food in through it's mouth.  If it is being fed a already chopped up feed, like chaff and grain it will take it up using it's lips, if it is eating grass it will use it's front teeth or incisors to chop the grass from the ground first.  Food is then moved back in the mouth by it's very large tongue - it is roughly the size of an adult female's forearm!  It is ground up by the back teeth using the premolars and molars before being swallowed.  The muscles used are the big masseter muscles on the cheeks.

Once swallowed the feed moves through to the esophagus which is between 1.2 - 1.4 metres in length which carries the food through to the stomach.  Horses are unable to vomit due to a muscular ring called the cardiac sphincter, which is very strong and well-developed and also placed at an angle.

Horses have very small  stomachs for their size, which is why they are most suited to grazing quite continuously (up to 16 hours per day) and when they have access to vast amounts of grazing land will travel long distances to choose what they forage on.  We keep horses in a much more intense environment so have to balance their diets as best as we can.  Anyway, off track a little because if I start yapping on about nutrition then this post may never end!  So horses have very small stomachs that can fit around 15 litres in them at a time.  It is most effective when 1/2 this volume approximately is being used because the stomach will empty when it is 2/3rds full regardless of whether the horse has processed the food or not.  It is better to have access to continuous forage, like hay if there is no pasture and if you need to bulk up with a hard feed for whatever the reason (like adding supplements) then you should make them small feeds.  When the feed leaves the stomach it exits through the pyloric valve, which controls the flow of the food out of the stomach.

The next part of their digestive process occurs in the small intestine.  This alone is between 15 - 21 metres in length.  It is where most of the digestive action happens and where most of the nutrients are absorbed by the body, including, proteins, simple carbohydrates, fats and the fat soluble vitamins A, D & E.  Horses do not have a gall bladder so bile flow is constant.  The bile from the liver is what helps to digest fats.  Anything left over then moves into the large intestine for the body to process.

As I mentioned before, the large intestine is broken into a few more sections.  The cecum is the 1st section of the large intestine, commonly referred to as the 'hind gut'.  It is about 1.2 metres long and holds 26 - 30 litres. It contains bacteria that use fermentation to digest what is left.  A horse cannot cope with too sudden a change in their diets because of the bacteria that live in the cecum.  The bacteria need time to adjust and modify in order to be able to process the new feeds.  If it cannot be broken down properly in this area then a horse is likely to colic.

The large colon is between 3 - 3.7 metres in length and can hold up to 76 litres of semi liquid matter.    The main purpose of the large colon is to absorb carbohydrate.  The large colon is a common place for a horse to get an impaction colic because it is a very twisty due to it's length, also the twisted bowel colic would likely occur here.

The small colon is also 3 - 3.7 metres in length.  It can only hold around 19 litres in comparison.  This is where the majority of water in a horses diet is absorbed and is where the balls of faeces are formed prior to expulsion.

The rectum is only around 30 centimetres in length and acts only as a holding chamber before the horse expels the left over waste via the anus.

Common Digestive System Disorders

Some signs that your horse's digestive system might not be working properly are:

  • Diarrhea
  • Constipation
  • Drooling
  • Loss of Appetite
  • Changes to faeces
  • Abdominal pain
  • Loss of gut sounds
  • Bloating
  • Dehydration

As you would likely guess by now, the digestive system is super important so referral to a qualified vet at any of these signs or changes is crucial so you can get a correct and accurate diagnosis and treatment for any of these symptoms.  It may be as simple as the horse needs a dental but could be as crucial as your horse might require surgery if appropriate.  Either way, any problems with the digestive system should be treated as serious.

Diarrhea can have many causes.  It can be caused by bacterial infections, malabsorption of nutrients or a viral infection - or may simply be because they are on very fresh, rich or wet pick in the paddock.  Either way - refer to a vet - especially if it is a sudden change and you don't know the cause!

Colic in horses is a common digestive disorder. It can be caused by so many different variables: change in diet, a stressful event, a foreign matter being ingested, dehydration and so on.  The signs of it are usually that a horse cannot defecate, a decrease in appetite, a rise in temperature and loss of gut sounds.  Your horse may also want to get away from the pain and discomfort in their abdomen so will likely look at their stomach, paw at the ground or want to repeatedly roll.  The last thing that you want them to do is to roll because it can then twist the intestines which is regularly fatal for the horse.  You should be contacting the vet for any suspected cases of colic so that your horse can be treated appropriately.  The sooner you can get them help the more likely their survival is depending on what has caused the colic.

Parasites can be another common cause of digestive system upset.  It is easy for the body to be invaded by parasites through the mouth.  It is important to have a good worming program in place for your horses so they cannot develop a resistance therefore allowing parasites to enter their system more easily.  Signs that your horse may have a parasitic infection are:

  • Scratching their tail
  • Messy anus
  • Malformed faeces
  • Weight loss
  • Dull coat
  • Loss or increase in appetite
  • Bloating

There are many products on the market to assist with controlling parasites in your horses and also as always your vet is a great resource to ask on what are the best control methods you should use in your particular case.

Stomach ulcers are also a problem in horses - I don't know now who said it but, "It is not a question of if your horse has ulcers - but when they get ulcers".  I have written a whole post on Ulcers that you can read here.

There are many other factors that can affect your horses digestive system but the bottom line is - your horse has a small stomach so should have access to small feeds and forage regularly as well as a fresh supply of water at all times.  A resting horse in Winter can drink up to 20 litres of water per day!  Don't skimp on it - and make sure it's fresh - taste it yourself!  And, if anything seems not right with your horses digestive system then make sure you refer to the vet.