The digestive tract starts at the mouth and ends at the anus. So it is a tube running through the body from the mouth to the anus. This tube’s contents are outside the body – like the hole in the doughnut.
The lining of the digestive tract keeps out the harmful and even deadly things to the horse. But it also allows in materials for fuel and maintenance of the various parts of the body. Selective absorption is the difference between the gut lining and the skin, which are otherwise the same.
Inside the digestive tract are a combination of acid, enzymes and bacteria. These are essential for the digestion of food and the horse’s survival. Attached is the liver, which is critical to many horse functions and deserves a separate chapter, but it is primarily a part of the digestive tract. It produces bile to digest fats, but because a horse doesn’t consume fat as part of the diet, it is unnecessary to make a lot and store it in a gall bladder. In addition, horses eat not in meals but in a steady intake for a major portion of the day. Therefore all horses are born without a gall bladder.
The digestive tract is a one-way street with all food pushed in one direction using muscular contractions (peristalsis) moving from the throat (esophagus) to the anus. Each section is divided into areas with specific purposes with specific acids, enzymes and gut bacteria. Suppose any of these materials are moved to a different location (change in pH, dysbiosis), produced in excess (increased acid production) or restricted (lack of an enzyme). In that case, a compromised digestive process occurs. Further, if the tube integrity becomes compromised, the unwanted contents will move across this membrane into the body (leaky gut syndrome).
Inflammation of the gut lining is a major concern with horses today. Many human researchers suggest that up to 90% of our immune system is located in the gut making the rest of the body weak against attacks from other invaders (viruses, bacteria). This high activity is because there is a lot of inflammation of the gut system as it receives foreign raw materials to handle. The result is a change in the gut’s normal materials (called dysbiosis), especially the resident bacteria, leading to the epidemic of horses with ulcers of the stomach, the small intestines and the colon.
To discuss the GI tract without discussing nutrition is pointless, so there will be a lot of overlap here and in the nutrition section under the CARE of the horse. The most serious issue in the digestive tract is colic, which strikes fear in horse owners. So many have lost at least one horse to this disease. However, I see many equally disturbing problems with the digestive tract, including diarrhea (squirts, free fecal water), stomach and colon ulcers, misbehavior and many metabolic issues. I will look at as many GI tract issues as I can, but you may hear a common cause – stop feeding the horse foods they were never supposed to eat: grain, grain byproducts, pointless minerals, vitamins and supplements. At best, you are wasting money getting an uncooperative horse. At worst, you are causing them to become ill and even die.