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Excerpt from Horse Digestion - It's Decidedly Different!


Now we move in to the hindgut where feedstuffs can remain for 36 to 48 hours. The hindgut encompasses the cecum, the large colon, the small colon, and the rectum. The cecum and large colon are the major sites of microbial fermentation and

absorption of fermentation products. 


The cecum is a fermentation vat very similar to a rumen but it has about 32 quarts in capacity compared to about 32 gallons the rumen holds, so itís about a fourth of the size. Nevertheless, it is pretty large and feed will stay in the cecum for about 7 

hours.In the cecum, billions and billions of bacteria and protozoa produce enzymes that can digest fiber.

The design of the cecum seems a little crazy, frankly. The entrance to the cecum from the small intestine is at the top and so is the exit into the large colon. The entrance and exit are also quite close together.

Picture this -- see diagram of digestive tract: You have all of this fiber that was not digested in the small intestine coming into the cecum where gravity pushes it to the bottom. The cecum is a very muscular organ that can contract and push on this forage

and mix it with water and digestive fluids and all of the bacteria and enzymes, but in order for the muscles to push the forage mixture out through the top to get to the large colon, the cecum needs to be full; it has to have enough volume of materials so 

that when it contracts, it squishes the matter out through the top. Itís like squishing a toothpaste tube on the bottom; it goes out through the top.

Imagine it this way: If the cecum is not full, then the process is hindered and the matter wonít get conducted into the large colon for the next stage of digestion. This can lead to impaction colic. Sand can also accumulate over time leading to sand colic. 

The answer? Feed the horse forage all the time, along with sufficient water. But be careful. Hindgut bacteria take time to adjust to a new feed, so make any feed changes gradually over a period of 2-3 weeks to give the bacteria time to adjust. Otherwise, 

your horse could colic. 


There are five different types of fiber Iíd like you to be aware of. Cellulose is a water insoluble fiber, as is hemicellulose. Cellulose and hemicellulose are digestible by the bacteria. Another fiber, lignin, is not. Lignin is like wood; the more mature the

grass is when itís cut to make hay, the more lignin it will contain.

If you look at your hay analysis report, it will show a number for neutral detergent fiber or NDF; this is a measurement of cellulose, hemicellulose, and lignin; this is the best measure of how digestible your hay is. If the number is high, over 60%, for

example, the hay will not provide very many calories for your horse because it will contain a lot of lignin.

There are two other kinds of fiber: pectin and mucilages. These are water-soluble fibers than form a gel which actually helsp push the fiber out of the cecum. Also if the horse has ingested any dirt or sand (a concern for sand colic) you may give him

psyllium (which is high n mucilages) for a week out of every month. that produces a gel that helps the sand move out of the cecum. Psyllium can be fed more often, even daily, depending on the soil condition in your horse's environment. A daily

dose of psyllium has also been shown to lower blood insulin by inhibiting glucose absorption.