Different areas of the horse’s gut carry out different actions in the process of digesting their feed. The total process from the mouth to the rectum can take 40 to 70 hours.
The Horse’s Mouth
It starts with the mouth where the teeth break up the feed and the saliva moistens it. While there is no digestion process, the saliva does act as a buffer to the acid in the stomach. It then passes down the oesophagus to the stomach where the next phase begins. The combination of the mouth, the oesophagus and the stomach are often referred to as the Foregut. To be sure the mouth is working efficiently, the teeth should be checked regularly by a professional.
The Horse’s Stomach
The horse has a small stomach when compared to the size of the horse. Unlike a human, the stomach has acid running 24/7. This is why it is so important that the horse has access to a regular intake such as grazing pasture and small additional feeds if required. The digestive process is able to adapt to different feeds, grasses , legumes , grain and processed food.
While minimal amounts of nutrients are absorbed from the stomach, there is some processing taking place. The muscular movement continues the breaking down of the food making it easier to pass on. Also, an enzyme called Pepsin is released and that acts on the protein and starts to change the structure.
The acid of the stomach (HCL) does not have any effect on the digestion but instead kills pathogens (bad bugs) that might be taken in with the food. The stomach stores the food for about 3-5 hours and then slowly releases it into the small intestine.
The Horse’s Small Intestine
It is here the process of the breaking down of the feed to create a state of absorbable nutrients begins. Enzymes are released, three types that act on starch, oil/fats and protein. They convert the starches into glucose, the fats into glycerol and fatty acids and the protein into amino acids. This breakdown converts food into nutrients that can pass through the gut wall and into the bloodstream.
The problem with the small intestine is that although it is about 21 metres long, food passes though quite quickly, approximately one hour. If there is a large quantity of starch (from grass, hay or grains), it is common that unprocessed starches and sugars are moved out of the small intestine and into the hind gut. This speedy movement also means that the absorption of important nutrients is reduced. Therefore, it is important that small feeds are given, and that horses are allowed access to grazing (or hay) 24 hours a day, little and often is the best management. Giving a horse a supplement with digestive enzymes will also help to prevent undigested feed moving to the hind gut where it causes pain and discomfort and therefore negative reactions by the horse.
The Horse’s Hindgut
From the small intestine, the feed passes into the hind gut. This is made up of the cecum, the large and small colons and finally the rectum. In the cecum ( a large sac) and large colon is where most of the microbial digestion takes place. Billions of beneficial bacteria and protozoa (known as microbes) assist the digestion by means of fermentation. Using a large volume of water, this action is primarily to break down the fibre content basically to VFA – volatile fatty acids that are an energy source. However, this process is disrupted if amounts of under processed carbohydrates have passed through from the small intestine and start to ferment. This creates a reaction that upsets the Ph as lactic acid is produced. This reaction is called Hindgut Acidosis and is painful and therefore a pain reaction from the horse occurs. For example touchy, grumpy, unwilling, negative and even colicky.
The other effect from the change in pH is that it actually kills off the beneficial bacteria reducing the effectiveness of the digestion process. Dying bacteria release a toxin that moves into the bloodstream and have the potential to trigger laminitis. Also, a low pH can favour pathogenic (bad) bacteria which can trigger serious diseases. Learn more here
B Vitamins and some amino acids are produced in the cecum and large colon, but these too are impacted if acidosis occurs.
The final part of the hindgut is the small colon whose main function is to reabsorb water, the digestion process has taken place and the indigestible remains are formed into balls and passed out via the rectum. Observation of the excretion will indicate a problem within the gut. Too dry and firm, or too loose and even showing diarrhoea is a sure sign of a poor digestive process.
Assisting the Digestion of the Horse
There are ways to help the horse with what they eat and how they eat.
Firstly, it is very important to allow access to green fodder, fibre in the forms of grass and legumes. If additional feed is required, then they should be small and fed two or three times during the day. No more than 2 Kg of a processed or grain-based feed at a time and always with some fibre source such as chaff.
Carbohydrates need to be digested in the small intestine so slowing down the speed of the passage will help to result in an efficient absorption. Together with supplementing with enzymes that assist with the breakdown of the starches and sugars. This will help prevent hindgut acidosis.
When difficulties in digestion have become apparent it is likely that loss of the microbiome ( the collection of microbes and protozoa) can be rectified with supplementing with a mix of pre and probiotics. This supplementing should also occur when a horse has been on a course of antibiotics (they kill good and bad bacteria). Or has been stressed or ill for a time.