The Significance Of Gut Sounds

As we continue to explore basic vital signs that help you and your veterinarian assess a horse’s health, let’s examine another critical parameter: intestinal activity. This is evaluated by listening to gut sounds using a stethoscope placed in the flank area on both sides of a horse, in each of four quadrants. Normal intestinal sounds are much like human stomach growls that are audible when we are hungry. Normally, two or three waves of intestinal contractions, called borborygmi, can be heard each minute in each quadrant. Intestinal sounds represent the mixing of intestinal contents and its progressive movement down the intestinal tract at a controlled rate, with some resistance to flow to allow absorption of nutrients and fluid in various portions of the bowel.

Changes in Intestinal Sounds

Depressed bowel activity is accompanied by diminished intestinal sounds. Instead of being digested, feed sits in one place and ferments, setting off a domino effect of problems. Although there may
not necessarily be a physical blockage of intestinal contents, a quiet bowel experiences a functional obstruction created by lack of effective intestinal motility. 

Other issues create specific sounds: 

• Gas in the bowel sounds similar to the tinkle of a pebble falling down a well.
• Squeaking noises indicate an attempt at peristaltic contractions with no progressive movement of material through the bowel.
• Increased activity of the colon is often associated with constipation or an impaction. 
• An excess amount of intestinal noise may indicate spasms or hyperactivity due to irritation in the bowel, or efforts to correct an obstruction. 

It is possible to “hear” the movement of sand by placing a stethoscope on the abdominal midline at the level of the girth, near the sternum. Sounds heard are similar to the sound of rolling surf on a sandy beach, or sand moving in a paper bag.

The Effects of Reduced Bowel Function

Gut sounds may only diminish in one portion of the abdomen rather than being absent altogether, hence the reasoning behind listening to all four quadrants. Stagnant intestinal activity reduces the absorption of intestinal water and nutrients from the bowel. Then vital fluids are sequestered in the gut, leading to whole body dehydration. Fluid is leached out of the intestinal contents of a stagnant bowel, potentially leading to an impaction. Feces may become sparse in frequency or amount. Or, mucoid strands may coat firm fecal balls, indicating stagnation of the large intestine, which could later lead to impaction colic. In some instances, the bowel may be irritated sufficiently to develop diarrhea which occurs as a consequence of a flaccid colon that offers no resistance to flow of ingesta down the “tube.”

Fermenting feed in a stagnant bowel changes the pH adversely to kill off normal intestinal flora, allowing for overgrowth of intestinal bacteria. With overgrowth of some comes death of others, with release of 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 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 solid phase change (e.g., larger particle size, increased particle stiffness) in a way that makes formation of a hard mass (i.e., an impaction) even more likely. 

Poor dentition also increases the risk of impaction by compromising mastication, which leads to a situation similar to what is seen with ingestion of poor-quality roughage: poor chewing results in intake
of larger particles. Thus, regular dental care is recommended.

Life-Style Effects on Intestinal Function

Alterations in motility, the water content within the colon, and changes in exercise are all considered as possible risk factors for colic. Events associated with an impaction include recent management change within two weeks prior to signs. One of the most frequently reported management changes is sudden restriction of exercise due to a musculoskeletal injury including hospitalization or restriction of exercise after surgery. Recent stall confinement is associated with about 54% of impaction colic cases; another study notes that 62% of colon impactions occur within two weeks of significant management changes, such as stall confinement or transport.  

Confinement may have multiple adverse effects on equine intestinal function. Stall-confined horses often experience inconsistencies in feeding intervals and amounts relative to previous management habits. The period of increased risk occurs when an active horse that has had regular exercise or turn out is suddenly confined to a stall. Ingestion of indigestible non-feed material such as shavings, sand, gravel, hard seeds, hair, pieces of rope or twine, rag and pieces of rubber can also lead to GI impaction. Although most horses would not eat these materials, some may develop vices or may be prone to strange eating behaviors due to conditions such as prolonged stall confinement or hunger. Thus, the time horses are kept in stalls should be minimized.

Ideally, horses confined to a stall should not be fed grain, as energy is rarely needed.  During periods of confinement or transport, use of bran mashes or other diet alterations has not been proven to prevent impactions. Additionally, feed modifications and diet changes have been incriminated in causing colic.  

Exercise incurs multiple benefits by increasing metabolism and improving intestinal motility. When possible, free choice exercise is best for horses, as some exercise appears to favor normal digestive processes with frequent intake of small amounts of feed over time. Just as changing the diet can be a challenge to some horses’ digestion, horses with sudden decreases in activity should be monitored closely for digestive problems that can lead to colic. Light physical activity like walking stimulates GI motility. Fiber digestibility increases by up to 20% in exercised horses, promoting greater retention of the fluid part of the diet and shortened retention of the more formed, particulate part of the feed. Progressive movement of particulate materials down the intestinal tract promotes efficient digestion while not allowing it to linger to form dehydrated intestinal contents.

Feeding in the period surrounding exercise is not without its own set of problems. Rigorous exercise just prior to feeding may decrease feed digestibility while blood remains shunted to working muscles, away from the intestinal tract. Strenuous exercise will shut down intestinal motility, so it makes sense to limit the amount of feed in the stomach or small intestine during exercise. Feeding forage at intervals during moderate or light exercise is appropriate. Take proper measures to adequately cool out a hot horse before feeding large meals, particularly grain.

Maintaining Normal Motility: Summary

Optimal equine health is based on normal intestinal activity and motility. 

• Feeding a diet of at least 50-60% fiber (hay, roughage, pasture) achieves optimum intestinal function. 
• Minimize the amount of grain or supplements fed, as these tend to be highly fermentable materials as well as contributing to possible consequences of gastric or colonic ulcers, laminitis, and poor behavior. 
• Deworm on a regular basis based on fecal egg counts to minimize the intestinal parasite load. 
• Provide plenty of clean water at all times.
• Regular exercise encourages drinking, appetite, and intestinal motility. 
• Take care of dental needs once or twice a year so a horse adequately chews his feed to derive the most nutrients and to minimize intestinal irritation.
• Monitor a horse’s daily manure output as well as feed intake. Observe the form, consistency, and quantity of the fecal balls, and know what is normal for each individual. 

Catching a problem while it is yet a small issue helps to prevent it surfacing into a full-blown colic.

Next Time

In the next installment, we will discuss Muscle Disorders. Stay tuned.