The GI tract of the horse is the fuel line that pulls and breaks down essential nutrients from feed — nutrients that are required for energy and optimal performance — and delivers them to the rest of the body. In this way, it also provides the basis of good overall health, physical development, muscle condition, external appearance and mental attitude.
In other words, your horse’s digestive health may be the key to everything that matters to you most.
Here’s a step-by-step guide to how the digestive tract functions in the course of digestion.
Just like you, horses use their teeth to grind, chop and break feed into smaller pieces. This physical breakdown is the first step of digestion. Chemical breakdown also occurs in the mouth thanks to saliva, secreted in response to chewing. The feed matter, called “ingesta,” is swallowed, carried down the esophagus to the stomach. Unfortunately, much of today’s processed grain or pelleted feed is consumed quickly by the horse. This results in less chewing, reducing saliva production and pre-digestion.
Ingesta enters the stomach, which contains a solution of the protein-digesting enzyme pepsin and hydrochloric acid. Saliva and fiber can help buffer the acid.
The stomach of the horse is relatively small, representing only about 5% to 10% of the entire capacity of the digestive tract. Because of this, feed only remains in the stomach for a short period — as little as 15 minutes. Feeding large meals of primarily grain, which are often consumed quickly, can result in insufficient contact with the gastric secretions in the stomach.
The small intestine is a long tube, approximately 70 feet long, where most feed nutrients are digested and absorbed. The small intestine is divided into three sections — the duodenum, the jejunum and the ileum. Various enzymes further break down the feed into component nutrients, and bile from the liver helps emulsify fats, breaking them into smaller units. These nutrients are then absorbed through the wall of the intestine to the blood stream and delivered throughout the body. In spite of the length, ingesta can move through the small intestine rapidly, especially with a high starch, low fiber diet, thus reducing the absorption of starches from these feeds.
Villi, tiny finger-like extensions, line the intestinal wall at an almost microscopic level. These villi increase the surface area of the intestinal wall — tissue known as mucosa — for maximum contact with the ingesta, to enhance the absorption of nutrients. Specialized cells within the mucosa of the small intestine, called enterocytes, have the specific function of carrying nutrients through the mucosal lining and into the bloodstream.
Because the enzyme amylase is in relatively short supply in a horse, the ability to digest starch in the small intestine is limited. As a result, the risk of undigested starch reaching the hindgut is significant in horses, especially those fed high grain diets.
Any material not digested in the small intestine is carried into the large intestine, which consists of the colon and the cecum. Combined, this represents most of the hind gut of the horse. It also makes up the majority of the capacity of the digestive tract — about 130 quarts.
The cecum is a large sac filled with millions of digestive microbes — bacteria and other micro-organisms that consume and ferment nutrients. In a normal equine diet rich in fiber, the digestive microbes in the cecum serve primarily to convert structural carbohydrates into various nutrients, including essential volatile fatty acids (VFAs) which provide a significant share of the horse’s energy. These nutrients are then absorbed in the colon.
When starch reaches the hindgut, it is fermented to produce lactic acid. This may increase the acidity of the gut (called “hindgut acidosis”), upsetting the balance of pathogenic bacteria. This may lead to lethargy, irritability, difficulty in bending or collecting, and general discomfort in the horse.
Learn how a Functional Feed™ program can support the health of the entire equine digestive tract. |