Ileus is a cause of colic in horses due to functional obstruction of the intestines. It most commonly seen in horses postoperatively, especially following colic surgery. Horses experiencing ileus are at risk for gastric rupture due to rapid reflux build-up, and require intense medical management with frequent nasogastric intubation. Ileus may increase adhesion formation, because intestinal segments have more prolonged contact and intestinal distention causes serosal injury and ischemia. It is usually treated with aggressive fluid support, prokinetics, and anti-inflammatories.

In primary chronic intestinal pseudo-obstruction (the majority of chronic cases), the condition may be caused by an injury to the smooth muscle (myopathic) or the nervous system (neuropathic) of the gastrointestinal tract.

In some cases there appears to be a genetic association. One form has been associated with DXYS154.

Secondary chronic intestinal pseudo-obstruction can occur as a consequence of a number of other conditions, including Kawasaki disease, Parkinson's disease, Chagas' disease, Hirschsprung's disease, intestinal hypoganglionosis, collagen vascular diseases, mitochondrial disease, endocrine disorders and use of certain medications. The term may be used synonymously with enteric neuropathy if a neurological cause is suspected.

Horses may develop pharyngitis, laryngitis, or esophagitis secondary to indwelling nasogastric tube. Other complications include thrombophlebitis, laminitis (which subsequently reduces survival rate), and weight loss. Horses are also at increased risk of hepatic injury.

Survival rates for DPJ are 25–94%. Horses that survive the incident rarely have reoccurrence.

Blind loop syndrome is a complication of surgical operations of the abdomen, as well as inflammatory bowel disease or scleroderma. Another cause is jejunoileal diverticula.

Prucalopride, pyridostigmine, metoclopramide, cisapride, and erythromycin may be used, but they have not been shown to have great efficacy. In such cases, treatment is aimed at managing the complications. Linaclotide is a new drug that received approval from Food and Drug Administration in August 2012 and looks promising in the treatment of chronic intestinal pseudo-obstruction, gastroparesis and inertia coli.

Intestinal stasis, which may lead to bacterial overgrowth and subsequently, diarrhea or malabsorption, is treated with antibiotics.

Nutritional deficiencies are treated by encouraging patients to avoid food high in fat and fibre, which are harder to digest and increase abdominal distention and discomfort, and have small, frequent meals (5–6 per day), focusing on liquids and soft food. Reducing intake of poorly absorbed sugar alcohols may be of benefit. Referral to an accredited dietitian is recommended. If dietary changes are unsuccessful in meeting nutritional requirements and stemming weight loss, enteral nutrition is used. Many patients eventually require parenteral nutrition.

Total parenteral nutrition (TPN) is a form of long-term nutritional treatment needed for patients that have severe pseudoobstruction. After a period of no improvement of intestinal function or motility the decision to start TPN will be made, and the surgical procedure to add a long-term, more permanent IV to administer TPN will occur. Types of IV catheters to be placed will be a PICC line or central line which include mediports, Broviac, or Hickman lines depending on how long the physicians believe the patient will require TPN. Patients that are deemed TPN dependent will require constant checkups to monitor the catheter is working properly, check liver enzyme levels and look for signs of blood infections, as catheter blockage, liver damage, and infections of catheters are the main complications associated with long term TPN use and can result in sepsis and/or additional surgeries if not properly monitored. TPN nutritional feeds are given over a period of several hours to all day infusions, and are a mixture of all the vitamins, minerals, and calories similar to what one would get eating orally daily as well as any other specific nutritional needs the patient has at the moment. TPN format is typically changed depending on loss/gain of weight and bloodwork results, and is specially formulated to meet each individual patient's needs.

Use of octreotide has been described.

Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. The plant cannabis has been used in clinics for centuries, and has been known to be beneficial in a variety of gastrointestinal diseases, such as emesis, diarrhea, inflammatory bowel disease and intestinal pain. Moreover, modulation of the endogenous cannabinoid system in the gastrointestinal tract may provide a useful therapeutic target for gastrointestinal disorders. While some GI disorders may be controlled by diet and pharmaceutical medications, others are poorly moderated by conventional treatments. Symptoms of GI disorders often include cramping, abdominal pain, inflammation of the lining of the large and/or small intestine, chronic diarrhea, rectal bleeding and weight loss. Patients with these disorders frequently report using cannabis therapeutically.

In a 2012 animal study, cannabichromene was shown to normalize gastrointestinal hypermotility without reducing the transit time. The study notes that this result is of potential clinical interest, as the only drugs available for intestinal dysmotility are often associated with constipation.

Paralysis of the intestine is often termed paralytic ileus, in which the intestinal paralysis need not be complete, but it must be sufficient to prohibit the passage of food through the intestine and lead to intestinal blockage. Paralytic ileus is a common side effect of some types of surgery, commonly called postsurgical ileus. It can also result from certain drugs and from various injuries and illnesses, such as acute pancreatitis. Paralytic ileus causes constipation and bloating. On listening to the abdomen with a stethoscope, no bowel sounds are heard because the bowel is inactive.

A temporary paralysis of a portion of the intestines occurs typically after abdominal surgery. Since the intestinal content of this portion is unable to move forward, food or drink should be avoided until peristaltic sound is heard, by auscultation (use of a stethoscope) of the area where this portion lies. Intestinal atony or paralysis may be caused by inhibitory neural reflexes, inflammation or other implication of neurohumoral peptides.

The overgrowth of bacteria in the small intestine is prevented by various mechanical and chemical factors which include the constant peristaltic movement of contents along the length of the gastrointestinal tract and the antibacterial properties of gastric secretions, pancreatic secretions and bile.

It follows that a disruption of any of these factors could lead to bacterial overgrowth and indeed BLS has been found to occur in persons with anatomical anomalies that result in stagnation. BLS has also been associated with achlorhydria, dysmotility, fistulae, and strictures. Chronic or high dose opioid therapy may contribute to BLS by reducing gastric motility.

Due to the disruption of digestive processes by the overgrowth of intestinal bacteria malabsorption of bile salts, fat and fat-soluble vitamins, protein and carbohydrates results in damage to the mucosal lining of the intestine by bacteria or via the production of toxic metabolites.

The prognosis for non-ischemic cases of SBO is good with mortality rates of 3–5%, while prognosis for SBO with ischemia is fair with mortality rates as high as 30%.

Cases of SBO related to cancer are more complicated and require additional intervention to address the malignancy, recurrence, and metastasis, and thus are associated with poorer prognosis.

All cases of abdominal surgical intervention are associated with increased risk of future small-bowel obstructions. Statistics from U.S. healthcare report 18.1% re-admittance rate within 30 days for patients who undergo SBO surgery. More than 90% of patients also form adhesions after major abdominal surgery.

Common consequences of these adhesions include small-bowel obstruction, chronic abdominal pain, pelvic pain, and infertility.

Risperidone, an anti-psychotic medication, can result in megacolon.

Toxic megacolon is mainly seen in ulcerative colitis and pseudomembranous colitis, two chronic inflammations of the colon (and occasionally, in the other type of inflammatory bowel disease, Crohn's disease). Its mechanism is incompletely understood. It is probably due to an excessive production of nitric oxide, at least in ulcerative colitis. The prevalence is about the same for both sexes.

In patients with HIV/AIDS, cytomegalovirus (CMV) colitis is the leading cause of toxic megacolon and emergency laparotomy. CMV may also increase the risk of toxic megacolon in non-HIV/AIDS patients with IBD.

It is a serious medical disorder and the mortality rate can be as high as 30%. The high mortality rate is likely a measure that this syndrome is seen in critically ill patients, rather than this syndrome being in itself lethal, although it can also present in otherwise healthy individuals (especially if the disorder was induced by pharmacologic agents). Drug induced megacolon (i.e. from Clozapine) has been associated with mortality as high as 27.5%.

The prevalence of diverticulosis progressively increases with age. Approximately 50% of people over the age of 60 and 70% of people over the age of 80 have diverticulosis. This disease is common in the U.S., Britain, Australia, Canada, and is uncommon in Asia and Africa. Large-mouth diverticula are associated with scleroderma. Diverticular disease is more common in collagen disorders such as Ehlers Danlos Syndrome.

Colitis is inflammation of the colon. Acute cases are medical emergencies as the horse rapidly loses fluid, protein, and electrolytes into the gut, leading to severe dehydration which can result in hypovolemic shock and death. Horses generally present with signs of colic before developing profuse, watery, fetid diarrhea.

Both infectious and non-infectious causes for colitis exist. In the adult horse, "Salmonella", "Clostridium difficile", and "Neorickettsia risticii" (the causative agent of Potomac Horse Fever) are common causes of colitis. Antibiotics, which may lead to an altered and unhealthy microbiota, sand, grain overload, and toxins such as arsenic and cantharidin can also lead to colitis. Unfortunately, only 20–30% of acute colitis cases are able to be definitively diagnosed. NSAIDs can cause slower-onset of colitis, usually in the right dorsal colon (see Right dorsal colitis).

Treatment involves administration of large volumes of intravenous fluids, which can become very costly. Antibiotics are often given if deemed appropriate based on the presumed underlying cause and the horse's CBC results. Therapy to help prevent endotoxemia and improve blood protein levels (plasma or synthetic colloid administration) may also be used if budgetary constraints allow. Other therapies include probiotics and anti-inflammatory medication. Horses that are not eating well may also require parenteral nutrition. Horses usually require 3–6 days of treatment before clinical signs improve.

Due to the risk of endotoxemia, laminitis is a potential complication for horses suffering from colitis, and may become the primary cause for euthanasia. Horses are also at increased risk of thrombophlebitis.

Horses are withheld feed when colic signs are referable to gastrointestinal disease. In long-standing cases, parenteral nutrition may be instituted. Once clinical signs improve, the horse will slowly be re-fed (introduced back to its normal diet), while being carefully monitored for pain.

DPJ is most commonly seen in the Southeastern US, although cases have been reported throughout the United States and Canada, as well as sporadically in the United Kingdom and Europe. Horses in the Southeastern US tend to have a more severe form of the disease relative to other locations. Age, breed, and gender appear to have no effect on disease prevalence.

Causes of large bowel obstruction include:

- Neoplasms / cancer

- Diverticulitis / Diverticulosis

- Hernias

- Inflammatory bowel disease

- Colonic volvulus (sigmoid, caecal, transverse colon)

- Adhesions

- Constipation

- Fecal impaction

- Fecaloma

- Colon atresia

- Intestinal pseudoobstruction

- Endometriosis

- Narcotic induced (especially with the large doses given to cancer or palliative care patients)

With early intervention, morbidity and mortality of cases of intestinal obstruction is low. The outcome is in part dependent upon congenital comorbidities and delays in diagnosis and management.

The condition is diagnosed most often in infancy and early childhood. It strikes about 2,000 infants (one in every 1,900) in the United States in the first year of life. Its incidence begins to rise at about one to five months of life, peaks at four to nine months of age, and then gradually declines at around 18 months.

Intussusception occurs more frequently in boys than in girls, with a ratio of approximately 3:1.

In adults, intussusception represents the cause of approximately 1% of bowel obstructions and is frequently associated with neoplasm, malignant or otherwise.

The predisposition to diverticulosis for specific individuals is likely explained by a genetic component, a theory which is supported by studies examining the rates of diverticulosis among twins. The heritability of diverticulosis is estimated to be approximately 40%.

Laparotomy for other forms of volvulus, especially anal volvulus.

Causes of intussusception are not clearly established or understood. About 90% of cases of intussusception in children arise from an unknown cause. They can include infections, anatomical factors, and altered motility.

- Meckel's diverticulum

- Polyp

- Duplication

- Appendix

- Hyperplasia of Peyer's patches

- Idiopathic

An earlier version of the rotavirus vaccine that is no longer used was linked to intussusception, but the current versions are not clearly linked. Due to a potential risk, they are thus not recommended in babies who have had intussusception.

Fecal vomiting, also called feculent vomiting and stercoraceous vomiting is a kind of vomiting wherein the material vomited is of fecal origin. It is a common symptom of gastrojejunocolic fistula and intestinal obstruction in the ileum. Fecal vomiting is often accompanied by an odor of feces on the breath and other gastrointestinal symptoms, including abdominal pain, abdominal distension, dehydration, and diarrhea. In severe cases of bowel obstruction or constipation (such as those related to Clozapine-treatment) fecal vomiting has been identified as a cause of death.

Fecal vomiting occurs when the bowel is obstructed for some reason, and intestinal contents cannot move normally. Peristaltic waves occur in an attempt to decompress the intestine, and the strong contractions of the intestinal muscles push the contents backwards through the pyloric sphincter into the stomach, where they are then vomited.

Fecal vomiting can also occur in cats.

Fecal vomiting does not include vomiting of the proximal small intestine contents, which commonly occurs during vomiting.

In a cecal volvulus, the cecum may be returned to a normal position and sutured in place, a procedure known as cecopexy. If identified early, before presumed intestinal wall ischemia has resulted in tissue breakdown and necrosis, the cecal volvulus can be detorsed laparoscopically.

Neonatal bowel obstruction (NBO) or neonatal intestinal obstruction is the most common surgical emergency in the neonatal period. It may occur due to a variety of conditions and has an excellent outcome based on timely diagnosis and appropriate intervention.

Fecal impaction and attempts at removal can have severe and even lethal effects, such as the rupture of the colon wall by catheter or an acute angle of the fecaloma (stercoral perforation), followed by septicemia. A small fecalith is one cause of both appendicitis and acute diverticulitis. It may also lead to stercoral perforation, a condition characterized by bowel perforation due to pressure necrosis from a fecal mass or fecaloma.