A change in the affected horse’s environment that minimizes their exposure to the cause is vital for both treatment and prevention of the vicious cycle of irritation and further airway destruction. Except for the case in which pasture grass pollen is the cause, affected horses may need to be kept outside and fed pasture forage or hay cubes, pellets, acid-treated hay, haylage, or silage. If loose hay must be used, it should be soaked for at least 5 minutes before being fed. This should be done by putting it in a haynet and immersing it completely in a tank of clean water, or by soaking it well with a hose before placing it inside the stall. Fungal spores released from hay are significantly reduced by soaking the hay for 5 minutes prior to feeding. If the grain is dusty, it shouldn’t be fed or should also be soaked prior to being fed. Wet feed not consumed should be replaced frequently, as it may mold. Adding up to 10% fat or oil to the diet, as described in Chapter 4, may also be of benefit in decreasing feed dust, increasing diet caloric density, decreasing diet bulk, and in providing dietary energy in the form which when metabolized produces the least amount of carbon dioxide for respiratory expiration. All feed should be fed close to the ground and not in a deep container, such as a feed trough, so that particles will tend to fall away from the horse’s nose and not be inhaled.
When the horse is stabled, it should be kept in a large well-ventilated stall with the top of an outside door or a window left open. Procedures for ensuring good stable ventilation, as described in Chapter 9, should be followed closely. Straw bedding should not be used, because it greatly increases air contamination (Table 9–7). Instead, wood chips, peat moss, shredded paper, or synthetic bedding material should be used, and the stall should be cleaned daily. Affected, and preferably all, horses should be removed from the stable during and for several hours after stalls are cleaned and bedded and hay is handled.
For these management procedures to be effective, they must be used for all horses sharing an air space with affected horses. For the occasional horse allergic to grass pollen, it must be kept off pasture during late spring, summer, and early fall. Most horses with heaves become symptom-free within 1 to 2 weeks and recover completely in 3 to 4 weeks after their exposure to the cause is minimized, although it takes longer for severe cases. A longer period of time is also required for a reduction in inflammatory secretions and, therefore, improvement in exercise tolerance and performance ability.
Horses in severe respiratory distress may be given corticosteroids, antihistamines, mucolytics, and bronchodilators to help alleviate the distress. However, in a controlled study, medical therapy using combinations of all these drugs did not improve affected horses. This emphasizes the necessity of management changes that minimize the horse’s exposure to the cause. Desensitization or immunotherapy is another option to try to prevent recurrence. In one study, it was beneficial in 66 of 99 horses with heaves.
DIARRHEA
Following, if necessary, correction of dehydration, feed should not be withheld from the diarrheic horse unless gastric distention, reflux, or bloating occurs. Feeds, and/or oral fluids either ingested or administered by stomach tube, are necessary in the gastrointestinal tract to maximize its integrity and healing ability. Lack of oral alimentation for more than 2 days, causes a loss of intestinal integrity and function that may contribute to a worsening of or decreased ability to recover from the diarrhea, and may result in disease-producing organisms and their toxins gaining access to the blood, causing septicemia, particularly in the young.
Regardless of the cause of diarrhea, small amounts of high-quality, highly digestible feeds should be fed, frequently. Overly mature and thus poorly digestible hay should be avoided.
If it has been determined that small-intestinal function is adequate, 0.5 to 0.6 lb/100 lbs (0.5 to 0.6 kg/100 kg) body wt/day of grain along with forage always available should be fed. Up to 20% vegetable oil (1 pt/5 lbs, or 20 ml/kg) may be added to the grain fed if additional dietary energy is needed for the maintenance of hydrated body weight. However, if small intestinal function, and as a result, grain utilization is greatly impaired, a primarily forage diet should be fed, as excessive grain intake may worsen the diarrhea. Grain or starch not absorbed in the small intestine pass into the large bowel where excess amounts alter microbial fiber fermentation, decreasing the nutrients derived from forages. Even when small-intestinal function is impaired, this problem can be decreased and at least some grain may be utilized by feeding small amounts frequently so that the intestinal digestive/absorptive capacity is not overwhelmed. Dietary fat, whether absorbed from the small intestine or not, improves energy digestion.
Regardless of the cause of diarrhea, fiber ingestion is beneficial as a source of volatile fatty acids, which, along with the amino acids glutamine and aspartate, are principle sources of energy for the intestine. Fiber may also stimulate intestinal segmental motility (which slows passage of intestinal contents) and add bulk and form to the feces. Because of these benefits, the diarrheic horse should have good-quality forage always readily available. If hydrated body weight is not maintained with forage alone, then grain may be fed in amounts up to 50% of the weight of the feed fed, or a complete pelleted feed containing both grain and forage may be fed with up to 20% vegetable oil added.
If antimicrobial drugs have been administered orally, beginning 2 to 3 days after their administration is stopped, or if there are other reasons to suspect that bacterial fermentation is abnormal, administering by stomach tube cecal or colonic fluid obtained from a horse with normal gastrointestinal function (preferably Salmonella negative), yogurt, or a commercial bacterial inoculant may be beneficial. Many of the organisms in cecal and colonic fluids are temperature sensitive; therefore, only fresh contents are likely to be of benefit, and if they need to be diluted, warm water should be used. Cecal and colonic fluids can sometimes be obtained from slaughter houses or dead horses but should be from those that did not have a digestive disturbance. If equine cecal fluid is unavailable, ruminal fluid instead may be of benefit as their microorganisms appear to be similar.
Sand-Induced Diarrhea
Sand and dirt may be ingested inadvertently with feed or purposely by some horses, particularly foals. Inadvertent consumption with feed is increased in horses on overgrazed and sandy-soil pastures, and when feed is consumed from the ground, particularly if the horses are underfed. The cause for purposeful consumption generally isn’t known. It can be, but generally isn’t, due to a nutrient deficiency (e.g., phosphorus, sodium or salt, or protein). Purposely eating dirt has been reported to occur as a result of severe intestinal parasitism, but parasitism is not present in most horses with sand-induced diarrhea. An insult to the gastrointestinal tract that alters intestinal motility, impeding the clearing of normal quantities of sand consumed with feed, may be responsible in some cases, and would explain the occurrence of single cases within a herd.
Ingested sand settles to the bottom of primarily the colon and cecum, where it causes damage and irritation-induced diarrhea. Obstructions and impactions may uncommonly occur. Most often there is a chronic diarrhea progressing over several weeks from pasty to semifluid to watery feces with chronic weight loss or poor growth and sometimes poor condition, or an inability to maintain weight compared to herdmates. For horses large enough for rectal palpation, sand may be detected on the sleeve used and may be palpated as a heavy ventral mass. In some, but not all cases, sand can be found in the sediment of a fecal emulsion with water. Although fecal sand excretion has been considered evidence of sand accumulation, a sufficient amount may not be excreted in some affected horses to suggest sand as the cause of the problem. In these cases, radiographic evidence of large amounts of sand in the gastrointestinal tract or sand excretion in response to treatment is necessary for diagnosis, although even with treatment sand excretion may not be consistently detected.
Treatment includes preventing additional sand ingestion and administering soluble-fiber bulk-inducing agents to increase fecal passage of ingested sand. Administering the soluble fiber, psyllium hydrophilic mucilloid (e.g., 3 to 4 oz/foal or 10 oz/adult horse of Metamucil—Searle Pharmaceuticals, or ½ lb or 225 g/adult horse or one-half this amount/foal of Modane—Adria Labs, twice daily) for 2 to 5 weeks in conjunction with a primarily forage diet has been found to be effective. The soluble fiber may be added to sufficient grain mix for its consumption or administered in a water emulsion by stomach tube. Sand-induced diarrhea will generally be resolved within 1 to 3 days of this management. However, treatment should be continued, as recovery may be slow due to sand accumulation, the time necessary for its passage, and chronic bowel inflammation. Infection in the abdominal cavity, but without intestinal rupture, may be present and requires appropriate antibiotic therapy.
Sand or dirt consumption, and thus the risk of sand-induced diarrhea, may be minimized by feeding psyllium daily and ensuring that adequate quantities of a diet consisting of 50 to 100% forage is fed up off the ground, or that the horse’s pasture is not overgrazed. Having trace-mineralized salt mixed with equal parts of bone meal available for free-choice consumption may also be helpful in decreasing voluntary sand consumption. In addition, the horses should be kept on a good deworming program as described in Chapter 9, and affected horses should be checked for intestinal parasites and treated accordingly. As with other oral vices or behaviors, as described in Chapter 20, decreasing confinement and providing increased exercise and companionship may be helpful in decreasing purposeful dirt consumption.
INTESTINAL IMPACTION
Normally small intestinal contents are semi-liquid. Intestinal contents become firmer in the large intestine where water is absorbed. If intestinal contents get too dry, they become doughy then firm. If the intestine can’t move this mass, or ingested foreign material (e.g., twine, rubber fencing material, etc.), an obstruction occurs resulting in pain from stretching of the intestinal wall by the mass and the intestinal build-up of bacteria-produced gas behind it. This is one of the most common causes of abdominal pain or colic, with colic being the most common medical problem of adult horses. Poor teeth that prevent proper chewing of feed, poor or high fiber feed, inadequate water intake, and ingestion of foreign material are causative factors.
Impaction with ingested feed is one of the most common forms of intestinal-obstruction-induced causes of colic in horses. Sand and intestinal calculi may also be responsible in some cases. Epsom salts (magnesium sulfate), and mineral oil administered by stomach tube are common treatments for feed-induced impactions in horses. Epsom salts has been shown to be an effective laxative in horses. Mineral oil, however, may coat but not penetrate the impacted mass, preventing water from gaining access to and thus disrupting the mass. Gentle manual massage through the intestinal wall of an impacted mass that can be reached by rectal palpation may disrupt the mass so it can be passed. The last, but sometimes necessary, resort is its surgical removal.
To assist in preventing impactions, ensure proper dental care as described in Chapter 9, that fresh palatable water is always readily available and that the horse gets regular exercise and a sufficient quantity of good quality feed. Following successful treatment of impaction, to prevent recurrence, high-fiber, poorly digestible feeds, such as mature forages and straw, should be avoided. Instead, feed low-fiber, highly digestible forages. A growing grass or legume is preferred, as they often produce a soft stool. A low-fiber, complete pelleted or extruded feed (Table 4–11) containing ground alfalfa may also soften the stools. Another alternative is to feed a diet consisting of one-half grain, which for maintenance would be 0.5 to 0.6 lb/100 lbs body wt (or 0.5 to 0.6 kg/100 kg) daily. If necessary to maintain a soft stool, 3 to 4 oz (90 to 120 g) of epsom salts (magnesium sulfate) and regular salt (sodium chloride may be added to the 1100-lb (500-kg) horse’s diet daily. Psyllium added to the diet as described in the previous section on sand-induced diarrhea may also be helpful.
INTESTINAL CALCULI (STONES)
Intestinal calculi or stones (enteroliths) cause impactions and colic and generally must be removed surgically. They form in the large intestine by mineral deposition around a nidus consisting of metal, cloth, or most commonly pebbles, and are composed primarily of magnesium ammonium phosphate (struvite). Their occurrence may be more common in Arabians and Morgans and in western and southern states, particularly California, Florida and Louisiana, although increased occurrences in Indiana and Illinois have also been reported. Their incidence is also high in some herds of zebras. Diets high in wheat bran—and thus high in phosphorus, calcium, magnesium, and protein—and alfalfa hay have been incriminated in their formation although conclusive evidence is lacking. However, several studies have indicated that when wheat bran was removed from the diet, the incidence of intestinal calculi decreased. Alfalfa also promotes alkalinity in the rumen and thus may do the same in the horse’s large intestine, which enhances calculi formation. Intestinal calculi have occurred in sufficient size to cause intestinal obstruction in horses as young as 11 months of age, although the mean age of occurrence is 10 years. Thus, intestinal calculi can grow to a size sufficient to cause intestinal obstruction within less than 1 year.
Intestinal calculi cause varying degrees of obstruction and pain depending on the amount of distention and vascular compromise caused. With partial obstruction, the horse will continue to pass scanty amounts of liquid feces, gas, or orally administered mineral oil. The first effect often noticed is a decrease in feed intake, which may become complete. Sometimes the calculus can be palpated rectally, particularly with the horse facing up a slope, allowing the intestinal tract to move back. They vary in location and may be single or multiple stones.
Because the incidence of enteroliths in horses is low and sporadic, and the incidence of recurrence unknown, the need for a diet to prevent their formation isn’t known. In species in which magnesium-ammonium-phosphate calculi commonly occur in the urinary tract, such as the dog and cat, feeding a diet low in protein (a source of ammonium), phosphorus and particularly magnesium that results in the maintenance of an acid urine has been shown to prevent their formation and to cause their dissolution. A similar type of diet may be of benefit for preventing formation of the same type of calculi in the intestinal tract of horses, although this hasn’t been demonstrated. A diet for the horse low in protein, magnesium and phosphorus may be obtained by feeding a grass forage and grain. Legumes, wheat bran, and, unless needed, protein supplements should be avoided. The horse’s water should also be low in magnesium and phosphorus or total solids.
Grass forages and cereal grains tend to be lower in magnesium (0.10 to 0.25% and 0.12 to 0.17%, respectively) than legumes (0.3 to 0.5%). Soybean meal contains about one-half as much magnesium as other oil seed meals (0.3 versus 0.6%). Wheat bran is relatively high in both magnesium and phosphorus (0.6 to 0.7% and 1.2 to 1.3%, respectively).
Feeding apple cider vinegar may also be of benefit, as it may acidify intestinal contents, which increases the solubility of these calculi. Adding ½, cup (110 ml) of apple cider vinegar per feeding of grain has been reported to acidify cecal fluid in ponies. At least twice this amount would be expected to be necessary to have the same effect in mature horses, and anecdotal reports indicate that when this amount is given twice daily, the incidence of intestinal calculi is decreased. Feeding a high-grain diet also acidifies intestinal fluid and thus would be expected to be of benefit. Thus, feeding a diet consisting of one-half grain (0.5 to 0.6 lb/100 lb body wt, or 0.5 to 0.6 kg/100 kg for maintenance), with 1 cup of vinegar added to it twice daily, and grass hay, while avoiding wheat bran and alfalfa, may be beneficial in preventing intestinal calculi formation in horses.
INTESTINAL REMOVAL OR DYSFUNCTION
Surgical removal of devitalized small or large intestine may at times be necessary and is compatible with resumption of a normal life if appropriate diets are fed.
Large-Colon Removal or Dysfunction
Immediately following removal of portions of the large colon, although fasting to allow bowel rest is often recommended, horses usually are able to eat high-quality feeds within 12 to 24 hours of surgery without adverse effects. The diet for the first month following surgery should be relatively high in protein (over 12%) and phosphorus (0.4%), and low in fiber (less than 28%) to compensate for a decrease in their apparent digestibility, which occurs for up to several weeks after surgical removal of the large bowel or inadequate blood flow to the large bowel without resection. A diet of this type can be provided by feeding a good weanling-type diet (Table 4–9). In addition, ensure that water is always easily available, as water losses and, therefore, needs are increased. Vitamin K administration may also be needed because of the loss of its production by cecal and colonic microflora. If the horse’s prothrombin, activated partial thromboplastic or blood clotting times are prolonged, vitamin K should be given.
The diet described should be continued for horses with extensive removal of both the left and right colons, as their apparent digestibility of protein, phosphorus, and fiber remains impaired. However, digestive ability and nutritional requirements return to normal in horses with removal of only the left colon or the cecum, and they are able to maintain adequate body condition on even a relatively low protein (6 to 8%) grass hay fed free choice.
Small-Intestinal Removal or Dysfunction
Following small-intestinal removal, the horse should be fasted for 1 to 3 days (1 if horse is in poor condition and up to 3 if in good body condition) to minimize the risk of disrupting suture lines and because of abnormal intestinal motility, although small amounts of a liquid diet may be offered or administered by stomach tube beginning the first day after surgery. The first day of feeding, give no more than one-quarter of that needed for maintenance, with a maximum of 2 lbs (1 kg) of good-quality hay, or a complete pelleted feed, per feeding every 2 to 4 hours. Gradually increase the amount fed over the next 2 to 3 days until estimated needs are met.
If less than one half of the small intestine has been removed or is dysfunctional, nutritional needs are not increased; whereas, they are if the amount is greater than this. Since grain is digested and absorbed primarily in the small intestine, and forage in the large intestine, a primarily forage diet should be fed, whether decreased small-intestinal function is due to its removal or to disease and dysfunction. The forage fed should be of high quality so that it is easily fermentable. Good-quality alfalfa or growing forage is usually best. Feeding small amounts of grain and fat may be beneficial if additional energy for maintenance of body weight and condition is needed. Calcium absorption, which is primarily from the small intestine, may be decreased, although supplementation is unlikely to be needed if a legume forage is being consumed because of legume’s high calcium content (Appendix Table 6). Alternatively a complete pelleted feed may be fed. Complete pelleted feeds fed in small amounts frequently maintained body weight and health of ponies with 70% of their lower small intestine removed. Fat-soluble vitamins A, D and E injections may be necessary if removal of the lower part of the small intestine results in sufficiently poor fat absorption.
RECTAL/VAGINAL SURGERY OR LACERATIONS
Decreasing fecal volume, pressure, and straining to defecate may be helpful following rectal or vaginal surgery or laceration repair in order to minimize pressure on the suture line. Defecation and stool volume can be nearly eliminated by tube-feeding a human commercial liquid diet. A lesser decrease in fecal volume, which is generally quite adequate following most rectal or vaginal surgery or lacerations, can be accomplished while still meeting the horse’s nutritional requirements by feeding a low-fiber (16 to 20%), high-energy complete pelleted diet (Table 4–11) along with up to 1 pint of vegetable oil/5 lbs of feed (20 ml/kg). This pellet-oil mix provides about 1.7 Mcal/lb (3.7 Mcal/kg), and thus 0.9 lbs/100 lbs (0.9 kg/100 kg)/day will meet the horse’s caloric needs for maintenance. Although a complete pelleted feed may be preferable, instead grain with up to the same amount of vegetable oil added may be fed as one-half of the horse’s total dry feed intake. For maintenance this would be about 0.6 lbs/100 lbs (0.6 kg/100 kg) body weight/day of both the grain-oil mix and forage. The forage may be a good-quality alfalfa hay or pellets, or green growing grass. Although fecal volume can be reduced by feeding less than needed, this isn’t recommended, at least not for more than a few days, as the resulting nutritional deficiencies it causes, if sufficient, will impair wound healing, and ability to resist disease.
LIVER DISEASE
Liver disease may result in central nervous system effects and behavioral alterations. These alterations and effects can be minimized by feeding diets adequate to meet dietary energy and protein needs, but without excess protein, and protein high in certain amino acids (branched chain) and low in others (aromatic).
Without adequate dietary energy intake, body glycogen, fat, and protein are utilized. Peripheral body fat mobilization, particularly in the animal with decreased liver function, may increase fat deposition in the liver, causing a further decrease in liver function. Body, like dietary, protein utilization for energy produces ammonia, which, if there is a decrease in its conversion to urea by the liver, increases plasma ammonia concentration. Sufficient body protein utilization, along with decreased liver production of plasma proteins, may result in decreased blood plasma protein concentration. If this is sufficiently severe, it results in edema (stocking up) or fluid in the abdominal or thoracic cavities, which may be worsened by high salt (sodium) intake and lessened by low salt (sodium) intake. To prevent or alleviate these effects, the diet for the animal with decreased liver function should meet the following criteria:
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