| Clinical signs of colic may arise due to obstruction, inflammation, or strangulating obstruction of the small intestine. The prognosis for conditions affecting the small intestine is often guarded. Hence, rapid diagnosis and appropriate treatment are critical. |
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Ileal Impaction: |
| The most common condition producing simple obstruction of the lumen of the small intestine is ileal impaction. It is most common in the southeastern USA, Germany, and The Netherlands. Although high-fiber hays may be important in the pathogenesis, a cause and effect relationship has not been proved. The results of recent clinical studies in the UK indicate that infection with the intestinal tapeworm
Anoplocephala
perfoliata
and ileal impaction are strongly associated. In a similar study performed in the USA, 2 risk factors for ileal impaction were identified—the lack of administration of pyrantel pamoate, an anthelmintic with some efficacy against
A
perfoliata
, within 3 mo and the feeding of Coastal Bermuda hay. Further, it has been suggested that the impaction develops secondary to spastic contractions of the ileal musculature against ingesta. |
| Clinical signs include the onset of mild to severe abdominal pain, followed by reduced intestinal sounds, gastric reflux, and tachycardia. Although early rectal examination may permit identification of the impaction in the ileum low in the right caudal abdominal quadrant, subsequent distention of the jejunum may make this identification difficult or impossible. The most common differential diagnosis is proximal jejunitis, and distinguishing the 2 conditions can often be
difficult. Because the horse’s condition initially may remain stable and the degree of abdominal pain may be mild, many horses with this condition are not referred for intensive care or surgery for >18 hr. The protein concentration of the peritoneal fluid may increase if the impaction has persisted for this long. |
| Treatment most often requires surgery, although it has also been reported that the condition responds to treatment with fluids and mineral oil, if identified early. If surgery is indicated, the impacted mass may be mixed with saline or carboxymethylcellulose and massaged into the cecum, or an enterotomy may be performed in the distal jejunum and the ingesta removed through the incision. Ileus may develop after surgery. Depending on the degree of damage to the serosal surface of
the small intestine at the time of surgery, complications may develop several weeks after surgery due to intra-abdominal adhesions (see below). |
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Adhesions: |
| Intra-abdominal adhesions generally affect the small intestine and usually cause obstruction of the intestinal lumen, although they may cause strangulating obstruction. These adhesions develop in response to peritoneal injury and, most often, are the result of previous small-intestinal surgery, chronic small-intestinal distention, peritonitis, or larval parasite migration. The tissue response to ischemia, traumatic tissue handling, foreign material, hemorrhage, or dehydration
results in the formation of fibrinous (and subsequently fibrous) adhesions. Clinical signs are seen if the adhesion causes kinking, compression, or stricture of the intestine. |
| Adhesions should be considered if the horse has had prior abdominal surgery and a more recent history of recurrent abdominal pain. Clinical signs associated with intra-abdominal adhesions range from mild, recurrent colic to severe unrelenting pain. Most commonly, intra-abdominal adhesions cause clinical signs within 90 days of the initial surgery if they are going to be a significant problem for the horse. |
| Surgical treatment involves transection of the adhesion, resection of the affected intestine, and anastomosis to achieve normal flow of ingesta. Therapeutic agents purported to reduce the subsequent formation of additional adhesions then are used. These include the systemic administration of antimicrobials, NSAID, and instillation of sterile carboxymethylcellulose into the abdomen at the time of closure. The owner should be informed that adhesions are likely to recur and that
the longterm prognosis for horses with extensive adhesions is poor. |
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Ascarid Impaction: |
| Young horses, particularly those on farms with inadequate parasite control programs, may develop ascarid impactions of the small intestine. These impactions are seen after administration of an anthelmintic with high efficacy against
Parascaris
equorum
. The anthelmintics most commonly associated with this condition are ivermectin, piperazine, and organophosphates. These drugs paralyze the ascarids, resulting in accumulation of masses of the worms in the small-intestinal lumen. It has been suggested that disruption of the surface of the ascarid releases antigenic fluids that inhibit intestinal muscular activity, thereby increasing the likelihood of intestinal obstruction. |
| Clinical signs range from mild to severe abdominal pain, evidence of toxemia, and gastric reflux that may contain ascarids. Ascarid impaction should be suspected if the affected horse is a weanling or yearling, in poor condition, and has a recent history of deworming. Medical treatment with fluids and intestinal lubricants may be successful in some cases. Other horses may require surgical intervention and removal of the ascarids through multiple enterotomies. The prognosis is
guarded if surgery has to be performed. The owner should be advised that other young horses on the premises should be treated with anthelmintics that have lower efficacy against ascarids, such as fenbendazole. These initial treatments can then be followed with more efficacious compounds. |
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Proximal Enteritis-jejunitis: |
| This poorly understood disease affects the proximal portion of the small intestine and has various names including proximal enteritis-jejunitis,
anterior enteritis, and duodenitis-jejunitis. The condition initially was recognized in the southeastern USA but has been reported to occur in the northeastern USA, England, and on the European continent. The cause is unknown. The affected intestine contains lesions varying from hyperemia to necrosis and infiltration of the submucosa with
inflammatory cells. Often, there is edema and hemorrhage in the various layers of the intestinal wall. |
| Varying degrees of abdominal pain, ranging from mild to severe, are characteristic. When the prevalence of the condition peaked in the 1980s, it was characterized by voluminous amounts of gastric reflux, progression from pain to depression, and moderate to severe distention of the small intestine on rectal examination. In addition, the distended duodenum often was palpated as it coursed around the base of the cecum. The peritoneal fluid often contained an increased
concentration of protein (>3 g/dL) with a normal number of WBC, but this finding did not consistently distinguish the condition from other causes of small-intestinal disease. Based on anecdotal reports, the prevalence and clinical severity of the condition have decreased in the past decade, at least in regions of the country where the condition characteristically had a more severe course and was accompanied by a high incidence of laminitis. |
| Treatment may be either medical or surgical. Medical treatment includes continued gastric decompression until the gastric reflux abates, IV fluids, and analgesics, as required. Many clinicians administer penicillin and low doses of flunixin meglumine; some also administer neostigmine, lidocaine, or metoclopramide to stimulate small-intestinal motility. Some surgeons, particularly in the UK, believe exploratory laparotomy and intestinal decompression result in a more rapid
recovery. The survival rate associated with proximal enteritis-jejunitis is reported to be 44%. |
| The feet should receive particular attention because acute laminitis has been reported as a common complication; the prevalence of acute laminitis in horses with proximal enteritis-jejunitis has been reported to be ~25%. |
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Intussusception: |
| Most intussusceptions that develop in horses are jejuno-jejunal, ileal-ileal, or ileocecal. The length of intestine that has become invaginated (the intussusceptum) into the more distal segment of intestine (the intussuscipiens) may range from a few centimeters to as much as a meter. Although the precise cause of most intussusceptions remains speculative, alterations in peristalsis due to enteritis, surgical trauma, parasite damage, anthelmintics, and
Anaplocephala
perfoliata
infection have been suggested. Horses <3 yr old are affected most commonly.
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| Abdominal pain may be either acute due to complete obstruction of the intestinal lumen or chronic due to partial occlusion of the lumen. If the occlusion of the intestinal lumen is complete, the horse is acutely painful and has gastric reflux, and distended loops of small intestine are palpable per rectum. It may be possible to palpate the turgid intussusception, especially if the ileum is involved. Because the strangulated intussusceptum is contained within the
intussuscipiens, the WBC count in the peritoneal fluid may not reflect the degree of intestinal damage. |
| Treatment requires surgery to reduce the intussusception, if possible, followed by resection and anastomosis. Due to the edema and hemorrhage in the wall of the affected intestine, it may be difficult to assess the viability of the bowel. Additionally, the damage to the intussusceptum may result in the development of adhesions. If the jejunum is involved, a jejuno-jejunal anastomosis must be performed. If the intussusception involves only the ileum, the affected intestine must
be resected and a jejuno-cecal anastomosis performed. If the ileum has invaginated into the cecum, the terminal portion of the ileum should be transected close to the cecum and a jejuno-cecal anastomosis performed. The prognosis for survival is good if surgery is performed before the intussusception has become irreducible. The prognosis is fair to poor in the latter case due to the development of peritonitis, ileus, adhesions, and abscess formation. |
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Volvulus: |
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A small-intestinal volvulus is seen when the intestine rotates on its mesenteric axis >180°. As the degree of the rotation increases, the vascular supply to the intestine is lost. Presumably because of its attachment to the cecum, the distal aspect of the volvulus is the ileum in most cases. |
| Horses with small-intestinal volvulus are acutely painful, and have an increased heart rate, a prolonged capillary refill time, and gastric reflux. Due to the loss of fluid into the intestine and stomach, these horses are dehydrated and have increased PCV and plasma protein concentrations. The horse’s status may deteriorate rapidly due to hypovolemia and endotoxemia. Rectal examination generally reveals turgid distended loops of small intestine, and the peritoneal fluid
contains increased numbers of WBC and protein. |
| Treatment involves surgical correction of the volvulus via a ventral midline celiotomy. If the intestine is nonviable, it must be resected and an anastomosis performed. The prognosis for survival depends on the duration of illness and amount of intestine that must be resected. Prognosis is good with early detection and surgery. Horses with a longer period of illness preoperatively, or postoperative ileus and peritonitis, are at increased risk for adhesion formation. It has been
suggested that euthanasia is warranted if >50% of the length of the small intestine must be removed. However, results of an experimental study in ponies indicated that removal of 70% of the small intestine did not result in malabsorption provided the ponies were fed several (8) small pelleted meals each day. |
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Pedunculated Lipomas: |
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Colic due to pedunculated lipomas is seen in horses >10 yr old. Pedunculated lipomas are suspended from the mesentery by a stalk or pedicle, which wraps around a segment of intestine, occluding the lumen of the intestine and interfering with its blood supply. The lipoma frequently forms a knot with the pedicle. |
| Clinical signs range from depression to severe abdominal pain, gastric reflux, and rapid deterioration in metabolic status. Distended loops of small intestine are palpable on rectal examination; the lipoma can also be felt per rectum in selected cases. The peritoneal fluid contains an increased number of WBC and RBC and an increased protein content. |
| Treatment requires transection of the pedicle and, if necessary, resection of the devitalized intestine. The prognosis depends on the time between onset of clinical signs and surgery. If surgery is performed early, the prognosis is good; however, if surgery is not performed until signs of cardiovascular deterioration are present, the prognosis for survival is fair to poor. |
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Internal Incarceration: |
| The most common sites for internal incarcerations are mesenteric rents and the epiploic foramen.
Mesenteric rents are defects in the small-intestinal mesentery. Problems develop when a segment of small intestine passes through the mesenteric defect, and the intestine becomes incarcerated. Because the intestine distends with fluid and blood, volvulus of the affected segment frequently occurs. Mesenteric rents are seen in horses of all ages. |
| The
epiploic foramen is a natural opening bounded by the caudate lobe of the liver, the portal vein, and the caudal vena cava. The distal jejunum and ileum are the most common portions of the intestine that become incarcerated through the epiploic foramen. Although generally the intestine passes from right to left to enter the omental bursa, it may pass in the opposite direction pushing the omentum ahead of it. Although it has been reported that horses >7 yr old are
affected most frequently, the results of recent studies indicate that the condition often develops in horses <7 yr old. |
| Clinical signs may be vague and similar to those of horses with proximal enteritis or pedunculated lipomas. The diagnosis may have to be made at surgery. Furthermore, in some cases, because of the position of the affected intestine within the omental bursa, the peritoneal fluid available for analysis may be normal. |
| Treatment of horses with either mesenteric rents or epiploic foramen entrapments is surgical. The affected segment of intestine must be exteriorized, its viability evaluated, and, if necessary, a resection and anastomosis performed. The prognosis for survival depends on the time between onset and surgery. If surgery is performed early in the course of the disease, the prognosis is good. However, because the clinical signs may be vague, the decision to perform surgery may be
delayed, worsening the prognosis. |
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Inguinal Hernia: |
| Inguinal hernias generally develop in stallions after breeding a mare, trauma, or a hard workout. Hernias appear to be most common in Tennessee Walking Horses, American Saddlebreds, and Standardbreds. In most cases, the hernia results in acute colic. The intestine descends through the vaginal ring in most cases and lies next to the testis and epididymis. Physical examination reveals a swollen testis that is firm and cool to the touch. If the hernia has occurred within hours,
the intestine may be palpated in the inguinal canal. In this situation, an attempt may be made to reduce the hernia by pulling down on the testis to tighten the boundaries of the inguinal canal and then forcing the intestine up toward the vaginal ring. Once the incarcerated intestine, which frequently includes the ileum, has become edematous, it is not possible to reduce the hernia manually. Rectal examination will reveal distended loops of small intestine, with one of the loops
tracing to the vaginal ring on the affected side. There will be gastric reflux, and the horse’s condition will deteriorate rapidly. Peritoneal fluid generally reflects the degree of ischemia. |
| Surgery involves a ventral midline celiotomy and inguinal approach to reduce the hernia. Often, the testicle on the affected side must be removed, and the affected intestine resected. The prognosis for survival seems to be breed-dependent, with Standardbred horses having a good prognosis and Tennessee Walking Horses having a fair to poor prognosis. Presumably, this reflects the fact that many Tennessee Walking Horse stallions with inguinal hernias show little evidence of pain. |
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