THE BASICS: THE DIGESTIVE SYSTEM
From chew to poo and everything in between!
|Horses have strong, mobile lips that can sort through food and allow grazing close to the ground. The incisor teeth break off the food and the molars grind it down as it is chewed. Chewing produces saliva which acts as a lubricant. The tongue passes the bolus of food to the back of the throat where it is swallowed into the oesophagus.|
|The OESOPHAGUS is a muscular tube leading from the mouth to the stomach. the lining of the oesophagus secretes mucus to help the movement of the bolus of food. The peristaltic movement of the muscles pushes the food down the oesophagus.|
|In a 16hh horse the STOMACH is about the size of a rugby ball and can stretch to hold about 8.5L. The upper part of the stomach is populated by bacteria which begin the job of fermenting sugars, starches and plant fructans. The lower part of the stomach produces gastric juices which contains hydrochloric acid. this acid neutralises bacteria an activates pepsin, an enzyme that acts on protein. The content of the stomach then passes into the small intestine.|
|Digestion of simple carbohydrates, fats and proteins is mostly completed in the SMALL INTESTINE. The length of the small intestine is approx. 20-27m and can hold 55-70L. it runs from the stomach to the caecum and is divided into 3 sections:DUODENUM (approx. 1m long); JEJUNUM (approx. 20m long); ILEUM (approx. 1-1.5m long). Peristaltic movement mixes the food with intestinal and pancreatic juices and bile. Amino acids, glucose, fatty acids and glycerol are absorbed through the lining.|
|From the small intestine, contents pass into the CAECUM. With a capacity of approx. 25-35L, fibrous parts of the food are mixed with digestive micro-organisms. When food enters the caecum this triggers the expulsion of the existing content into the colon, which stimulates intestinal activity all along the colon.|
|Once content is expelled from the caecum, it enters the LARGE COLON which can hold approx. 100L. This is the area where hind gut fermentation occurs. The large colon hosts billions of micro organisms that digest the fibrous parts of the horse's food, the cellulose and hemicellulose from plant matter. The hind gut also absorps vitamins, salt and water.|
|RECTUM: Horses poo an average of 10-12 times a day. Changes from normal consistency can indicate a short term adaptation or a more serious problem.
Loose, semi formed stools can be a result of stress, a diet change, turn out onto spring grass, a mare on heat. Often this only last for the short term.
|!!! Dental problems can interrupt this very first stage of digestion. Sore, sharp teeth can cause pain which can impact on chewing. Dropped food is often a sign that it is time to call the dentist.|
|!!! If food becomes stuck in the oesophagus this is known as choke.|
|!!! Horses are 'trickle' feeders, their system is designed to have a regular amount of forage passing through. Regular chewing produces saliva which contains bicarbonate, this helps neutralise stomach acid. Horses on restricted grazing, or who have their main feed intake in spaced meals, may be more prone to stomach ulcers, as they are doing less regular chewing and producing less acid buffering bicarbonate.|
|!!! Aged horses may be at risk of hypochlorhydria which is an underproduction of gastric acid, which would cause an incomplete digestion of protein, and for mineral supplements not to dissolve properly.|
|!!! Motility can become sluggish without the stimulation effects of food entering into the large intestine. Various locations in the bowel can act as a 'bottleneck' (where it narrows or makes a tight turn), and with sluggish motility contents in these areas can become too dry, which can lead to impaction.|
|!!! The micro organisms in the large colon are very susceptible to dietary changes. Disrupting the balance of micro organisms can lead to diarrhoea, colic and laminitis.|
|!!! The large colon can move around quite a bit in the abdomen so it needs to be weighed down with a normal degree of fibrous material to reduce the likelihood of displacement or twisting - common causes of colic.|
|!!! Dry, very firm balls of manure can indicate constipation.|
|!!! Diarrhoea is very liquid and often explosive and should be a cause for concern.|