Page 126 - April2022

VETERINARY VIEWS
endotoxin, a component of the outer membrane of the cell wall of Gram-negative bacteria. Endotoxin is absorbed easily from devitalized intestinal lining that occurs subsequent to reduced circulation related to dehydration or infection. Endotoxin itself is not poisonous,
but rather it elicits a chain reaction of activity
of other inflammatory chemical mediators in the body that deteriorate the system. One vital sign we discussed before – mucous membranes – develop margination (purple discoloration) along the gum line in the presence of endotoxin.
A horse may stop eating because of a feeling of intestinal “fullness” due to gas and fluid sequestration in a stagnant bowel. At times, the intestines become hyper-motile in an attempt
to “squeeze” out a forming impaction with gut sounds seemingly active initially. Yet with time, intestinal sounds may become absent altogether, a dangerous condition known as ileus. This adds to decreased absorption of intestinal water and electrolytes, worsened dehydration, devitalized bowel lining, increased fermentation of intestinal contents, more endotoxin and exotoxin uptake,
a drying out of intestinal contents, and a cycle of deterioration continues. Guts that cease motility set up conditions for intestinal displacement
or twists to occur in addition to metabolic complications encountered by endotoxin circulation and ongoing dehydration.
EFFECTS OF FEEDING STRATEGIES ON INTESTINAL FUNCTION
Horses evolved to graze small amounts of fiber-rich plants for 13 to 15 hours a day, and this style of eating avoids overfilling of the stomach. Not all horses have access to pasture, and not all horse owners can be present to feed small meals throughout the day.
Feeding large meals twice a day, particularly grain, has profound effects on intestinal function. Increasing dietary grain decreases the
Endotoxin - a toxin present in bacterial cells that is released when the cell disintegrates - itself is not poisonous, but it causes a chain reaction of other inflammatory chemicals in the body that worsen the system.
amount of water in the colon, perhaps creating conditions for impaction. Horses that are fed a large grain meal twice a day experience a 15% reduction in plasma volume within 30 minutes of each meal. In contrast, there is no change in plasma volume in horses that are fed smaller amounts every few hours. Feeding grain decreases the amount of fiber in the diet, which decreases the water content of the colon and alters fermentation to produce more gas. The changes that are created by twice daily feeding of grain set up conditions for extremes in fluid exchange in the colon, which can dehydrate the ingested feed and potentially set up conditions that lead to simple or severe colic.
For every pound of feed ingested, a horse needs 2-4 pints of water for digestion. This means that a 1000-pound horse consuming 20 pounds of food each day needs a minimum
of 7.5 gallons (or 30 liters) of water to process the feed material. This is the amount necessary solely for intestinal function; additional water
is necessary for other bodily maintenance functions, and even more for athletic endeavors. Inadequate intake of water for any reason causes dehydration and drying out of fecal contents. This may occur due to lack of water availability, frozen water, or polluted or contaminated water. Also, it is noteworthy that pelleted roughage requires a lot of water for digestion and has a potential to lead to impaction if water intake is restricted for any reason.
Dehydration of colonic contents is not
the whole story, however. There are other important mechanisms that contribute to intestinal transit, things like viscosity of the food material, diameter of the ‘tube’ through which ingesta flows, and pressures within the intestine that progressively propel materials toward the rectum while retaining them in bowel sections long enough to extract nutrients. In addition, offering a large meal only twice daily may interfere with activity of intestinal microbes that are responsible for efficient digestion of fiber.
Overfeeding of indigestible material such as poor-quality hay is thought to be a significant contributing factor to the development of an impaction. Avoid mature grass or any feed composed of poorly digestible fiber. Whenever hay or grass is fed, the contents of the large intestine have two distinct phases: a solid phase, composed of undigested pieces of grass; and a liquid phase. This liquid phase is loose and can be moved independently from the solid phase, leaving behind a mass of solid particles that can form an impaction. If poor quality roughage is fed, the properties of the
Increasing dietary grain decreases the amount of water in the colon and can create conditions favorable for impaction.
Offering large meals twice daily can interfere with activity of intestinal microbes that are responsible for efficient digestion of fiber.
124 SPEEDHORSE April 2022