Equine Digestive System

The anatomy of the horse's digestive system is fairly simple and straightforward, as it is much like yours with only a few minor differences. Starting from the top, the digestive system is composed of:

• the mouth and teeth
• esophagus
• stomach
• small intestine
• cecum
• large colon
• small colon
• rectum
• anus

The major difference between the horse and you is the importance of the cecum to the horse, whereas our appendix (which is the closest thing to the horse's cecum) is almost non-functional in humans.

Almost all digestion of simple carbohydrates, protein, and fat takes place primarily in the small intestine, though it begins in the stomach. Simple carbohydrates (starches and sugars) and protein begin digestion in the stomach by being slightly broken down, and then the majority of the digestion of these nutrients occurs in the small intestine. Fats are slightly hydrolyzed by enzymes in the stomach, but the majority of fat digestion also occurs in the early small intestine.

Mouth and Teeth: 

The mouth is very important as it is where digestion begins.The teeth harvest the feed, and when the horse is grazing act as the prehensile organ, which means they bring the grass into the mouth. The upper lip is the main prehensile organ when your horse is eating grain and other loose feeds.

The teeth also break down the feed so that the horse can swallow (masticate) it, and so digestion can more easily take place later in the tract.The salivary glands also play an important role in digestion. These glands produce saliva which is essential not only to moisten the food and assist its movement through the tract, but also as the beginning of carbohydrate digestion.

Esophagus:

The esophagus is pretty simple, as it is simply a passageway from the mouth to the stomach. It has rings of muscle around it that relax and contract to move food down towards the stomach, a process known as peristalsis.

Stomach:

This is where digestion really begins. Acid (specifically hydrochloric acid) and enzymes start to break down all the various nutrients (carbohydrates, fats, proteins) in the stomach.

The stomach makes up approximately 9% of the horse’s total digestive system, making it relatively small compared to body size. In comparison, your stomach makes up approximately 17% of your total digestive tract.

This small size is important to keep in mind. It is one part of the horse anatomy that makes the digestive tract of the horse so delicate.

Small Intestine:

After the stomach comes the small intestine, where almost all absorption of nutrients occurs. Various secretions are put into tract at the beginning of the small intestine allowing the nutrients to be broken up more thoroughly than the stomach did.

The small intestine has three “sections” which altogether make up about 35% of the entire tract - the duodenum, jejunum and ileum. The jejunum and beginning of the ileum is where most nutrients are absorbed, though some are absorbed in the duodenum.

The inner lining of the small intestine is lined with little projections called villi. Villi look like a bunch of little fingers stuck to the lining, and their purpose is to increase surface area. The more surface area, the more nutrient absorption.

Cecum:

This is where your horse varies greatly from you. Your cecum is basically non-existent, while your horse’s makes up 16% of his total digestive anatomy!

The cecum is at the beginning of the large intestine and is a “blind sac” -- it only has one opening, so everything has to go back out the same opening it goes in. Feed goes in, spends time being mixed around and digested by the microbes, and exits again into the rest of the large intestine.

This is another place where the horse anatomy makes the digestive tract delicate -- if something gets stuck in there, everything gets backed up, and you end up with big problems...usually colic.

In the cecum, microbes ferment and break down the fiber that your horse consumes in his forage. This provides him with important nutrients such as volatile fatty acids and some amino acids that would otherwise be wasted.

During evolution, some mammals developed a symbiotic relationship with microbes -- the microbes break down feed that the host (your horse in this case) could not otherwise use, and in return, the microbes get a “safe” place to live inside the host. Since mammals don’t make the enzymes necessary to break down the feeds that the microbes love, the relationship works well.

Colon:

The large and small colon is where your horse reabsorbs most of the water that is present in the digestive tract. This is also where wastes from body functions are secreted in preparation for being passed out of the body.

Microbial fermentation continues along the length of the colon. The colon makes up approximately 45% of the horse’s digestive tract, compared to 17% of yours.

Since the colon is so large, it is another place where the horse anatomy makes the digestive system delicate -- there are so many twists and turns that it is easy for it to get kinked or twisted, causing various types of colic.

Rectum and Anus:

This is the last part of the horse anatomy in the digestive system. The rectum is the last section of colon that is in the pelvic area, and the anus is the opening at the end of the tract.

Digestive Quiz

1. List the types of digestive systems of horses.
2. List the components of the foregut.
3. What are the signs that a horse needs to have its teeth floated?
4. What keeps a horse from being able to belch or vomit, and what are some consequences of this?
5. What nutrients are absorbed in the small intestine?
6. List the components of the hindgut.
7. What makes up the large intestine?
8. Is it normal to hear gut sounds?
9. Where do volatile fatty acids come from, and how do they benefit the horse?
10. List some factors that can influence digestibility.

Answers

1. Ruminants, Nonruminants, Hindgut fermenters
2. Mouth, Esophagus, Stomach, Small intestine
3. Head sideways, Dropping grain, Excess salivation when chewing
4. The sphincter at the junction of the esophagus and stomach is one-way;excess gas produced can rupture the stomach and cause the horse to die.
5. Carbohydrates, Vitamins, Fat Minerals, Protein
6. Cecum, Small colon, Large colon, Rectum
7. Large colon, Rectum, Small colon
8. Yes, it is normal to hear the mixing activities of the cecum.
9. From broken down fibrous feeds; they are a source of energy
10. Type or source of feedstuff, frequency of feeding, level of feed stuff maturity, rate of passage, processing method, compounds that interfere with digestibility

Digestive Flash Cards/Online Quizzes

http://quizlet.com/6091548/horse-4-h-digestive-system-flash-cards/

http://www.proprofs.com/quiz-school/story.php?title=digestive-system-practice-quiz 

http://quizlet.com/18917584/equine-anatomy-abdomendigestive-system-flash-cards/ 

http://www.funtrivia.com/trivia-quiz/Animals/Digestive-System-Of-The-Horse-149780.html

http://www.purposegames.com/game/digestive-system-of-the-horse-game

Digestion Videos

https://www.youtube.com/watch?v=8lqk7igz9L4 

https://www.youtube.com/watch?v=sKN0p-8E1GA

Related Articles

http://equinenutritionnerd.com/2014/06/29/the-equine-digestive-system/

http://www.succeed-equine.com/equine-health/the-healthy-equine-digestive-system/