Gastroscopy, or endoscopic evaluation of the stomach, is useful in chronic cases of colic suspected to be caused by gastric ulcers, gastric impactions, and gastric masses. A 3-meter scope is required to visualize the stomach of most horses, and the horse must be fasted prior to scoping.

Radiographs (x-rays) are sometimes used to look for sand and enteroliths. Due to the size of the adult horse's abdomen, it requires a powerful machine that is not available to all practitioners. Additionally, the quality of these images is sometimes poor.

Stable patients presenting to A&E (accident and emergency department) or ER (emergency room) with severe abdominal pain will almost always have an abdominal x-ray and/or a CT scan. These tests can provide a differential diagnosis between simple and complex pathologies. However, in the unstable patient, fluid resuscitation and a FAST-ultrasound are done first, and if the latter is positive for free fluid, straight to surgery. They may also provide evidence to the doctor whether surgical intervention is necessary.

Patients will also most likely receive a complete blood count (or full blood count in the U.K.), looking for characteristic findings such as neutrophilia in appendicitis.

Traditionally, the use of opiates or other painkillers in patients with an acute abdomen has been discouraged before the clinical examination, because these would alter the examination. However, the scientific literature does not reveal any negative results from these alterations.

It is important to differentiate DPI from small intestinal obstruction, since obstruction may require surgical intervention, but this can at times be difficult. Horses suffering from DPI usually have a higher protein concentration in their peritoneal fluid compared to horses with small intestinal obstruction, often without a concurrent increase in nucleated cell count. They usually have some relief and decrease in pain after gastric decompression, while horses with an obstruction often still act colicky after nasogastric intubation. Distention of the small intestine may be less than what is felt on rectal examination of horses with obstruction, especially after gastric decompression. Horses with DPJ usually produce larger volumes of reflux (usually greater than 48 liters in the first 24 hours) than those with obstruction, and are often pyretic (temperatures of 101.5–102.5) and have alterations in white blood cell levels, while those with obstructions usually have a normal or lower than normal temperature and normal leukocyte levels.

Ultrasound can also be helpful to distinguish DPJ from obstruction. Horses with small intestinal obstruction will usually have an intestinal diameter of −10 cm with a wall thickness of 3–5mm. Horses with proximal enteritis usually have an intestinal diameter that is narrower, but wall thickness is often greater than 6mm, containing a hyperechoic or anechoic fluid, with normal, increased, or decreased peristalsis. However, obstructions that have been present for some time may present with thickened walls and distention of the intestine.

DPJ can only be definitively diagnosed during surgery or at necropsy, when its gross appearance of the small intestine may be evaluated.

Diagnosis is guided by the person's presenting symptoms and laboratory findings. The gold standard imaging modality for the presence of gallstones is ultrasound of the right upper quadrant. There are many reasons for this choice, including no exposure to radiation, low cost, and availability in city, urban, and rural hospitals. Gallstones are detected with a specificity and sensitivity of greater than 95% with ultrasound. Further signs on ultrasound may suggest cholecystitis or choledocholithiasis. Computed Topography (CT) is not indicated when investigating for gallbladder disease as 60% of stones are "not" radiopaque. CT should only be utilized if other intraabdominal pathology exists or the diagnosis is uncertain. Endoscopic retrograde cholangiopancreatography (ERCP) should be used only if lab tests suggest the existence of a gallstone in the bile duct. ERCP is then both diagnostic and therapeutic.

Proximal enteritis usually is managed medically. This includes nasogastric intubation every 1–2 hours to relieve gastric pressure secondary to reflux, which often produces to 2–10 L, as well as aggressive fluid support to maintain hydration and correct electrolyte imbalances. Maintaining hydration in these patients can be very challenging. In some cases, fluid support may actually increase reflux production, due to the decreased intravascular oncotic pressure from low total protein and albumin levels, leading to loss of much of these IV fluids into the intestinal lumen. These horses will often display dependent edema (edema that collects in locations based on gravity). Colloids such as plasma or Hetastarch may be needed to improve intravascular oncotic pressure, although they can be cost prohibitive for many owners. Reflux levels are monitored closely to help evaluate fluid losses, and horses recovering from DPJ show improved hydration with decreased reflux production and improved attitude.

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used for pain relief, reduction of inflammation, and for their anti-endotoxin effects, but care must be taken since they may produce gastrointestinal ulceration and damage the kidneys. Due to a suspected link to "Clostridial" infection, anti-microbials are often administered, usually penicillin or metronidazole. Aminoglycosides should be used with extreme caution due to the risk of nephrotoxicosis (damage to the kidney). The mucosa of the intestines is damaged with DPJ, often resulting in absorption of endotoxin and risking laminitis, so therapy to combat and treat endotoxemia is often employed. This includes treatment with drugs that counteract endotoxin such as Polymyxin B and Bio-Sponge, fluid support, and laminitis prevention such as icing of the feet. Prokinetic drugs such as lidocaine, erythromycin, metoclopramide, and bethanechol are often used to treat the ileus associated with the disease.

Horses are withheld food until reflux returns to less than 1–2 L of production every 4 hours, and gut sounds return, often requiring 3–7 days of therapy. Parenteral nutrition is often provided to horses that are withheld feed for greater than 3–4 days. It is suspected to improve healing and shorten the duration of the illness, since horses often become cachexic due to the protein losing enteropathy associated with this disease.

Surgery may need to be performed to rule out colic with similar presenting signs such as obstruction or strangulation, and in cases that are long-standing (> 7 days) to perform a resection and anastomosis of the diseased bowel. However, some horses have recovered with long-term medical support (up to 20 days).

If a horse is suspected of choke, a veterinarian will often pass a stomach tube down the animal's esophagus to determine if there is a blockage. Failure to access the stomach with the tube indicates a complete obstruction; difficulty passing the tube may represent a stenosis, or narrowing; or a partial obstruction. Radiography and endoscopy are also used in refractory cases.

Choking horses should be deprived of food and drink pending veterinary attention, so as not to increase the obstructive load within the esophagus. The veterinarian will often sedate the horse and administer spasmolytics, such as butylscopolamine, to help the esophagus to relax. Once the muscles of the esophagus no longer force the food down the throat (active peristalsis), it may slip down on its own accord. If spasmolytics do not solve the problem, the veterinarian will usually pass a stomach tube through one of the nostrils and direct it into the esophagus until the material is reached, at which point "gentle" pressure is applied to manually push the material down. Gentle warm water lavage (water sent through the stomach tube, to soften the food material) may be required to help the obstructing matter pass more easily, but caution should be exercised to prevent further aspiration of fluid into the trachea.

Refractory cases are sometimes anesthetised, with an orotracheal tube placed to prevent further aspiration and to allow for more vigorous lavage. Disruption of the impacted material can sometimes be achieved via endoscopy. If these methods still do not lead to results, the horse may require surgery to remove the material.

Some workers have advocated the use of oxytocin in choke, on the grounds that it decreases the esophageal muscular tone. However, this technique is not suitable in pregnant mares, as it may lead to abortion.

It is unclear whether those experiencing a gallstone attack should receive surgical treatment or not. The scientific basis to assess whether surgery outperformed other treatment was insufficient and better studies were needed as of a SBU report in 2017. Treatment of biliary colic is dictated by the underlying cause. The presence of gallstones, usually visualized by ultrasound, generally necessitates a surgical treatment (removal of the gall bladder, typically via laparoscopy). Removal of the gallbladder with surgery, known as a cholecystectomy, is the definitive surgical treatment for biliary colic. A 2013 Cochrane review found tentative evidence to suggest that early gallbladder removal may be better than delayed removal. Early laparoscopic cholescystectomy happens within 72 hours of diagnosis. In a Cochrane review that evaluated receiving early versus delayed surgery, they found that 23% of those who waited on average 4 months ended up in hospital for complications, compared to none with early intervention with surgery. Early intervention has other advantages including reduced number of visits to the emergency department, less conversions to an open surgery, less operating time required, reduced time in hospital post operatively. The Swedish agency SBU estimated in 2017 that increasing acute phase surgeries could

free multiple in-hospital days per patient and would additionally spare pain and suffering in wait of receiving an operation. The report found that those with acute inflammation of the gallbladder can be surgically treated in the acute phase, within a few days of symptom debut, without increasing the risk for complications (compared to when the surgery is done later in an asymptomatic stage).

Right upper quadrant abdominal ultrasound is most commonly used to diagnose cholecystitis. Ultrasound findings suggestive of acute cholecystitis include gallstones, fluid surrounding the gallbladder, gallbladder wall thickening (wall thickness over 3 mm), dilation of the bile duct, and sonographic Murphy's sign. Given its higher sensitivity, hepatic iminodiacetic acid (HIDA) scan can be used if ultrasound is not diagnostic. CT scan may also be used if complications such as perforation or gangrene are suspected.

Colic is diagnosed after other potential causes of crying are excluded. This can typically be done via a history and physical exam, and in most cases tests such as X-rays or blood tests are not needed. Babies who cry may simply be hungry, uncomfortable, or ill. Less than 10% of babies who would meet the definition of colic based on the amount they cry have an identifiable underlying disease.

Cause for concern include: an elevated temperature, a history of breathing problems or a child who is not appropriately gaining weight.

"Red flag" indicating that further investigations may be needed include:

- Vomiting (vomit that is green or yellow, bloody or occurring more than 5/day)

- Change in stool (constipation or diarrhea, especially with blood or mucous)

- Abnormal temperature (a rectal temperature less than or over

- Irritability (crying all day with few calm periods in between)

- Lethargy (excess sleepiness, lack of smiles or interested gaze, weak sucking lasting over 6 hours)

- Poor weight gain (gaining less than 15 grams a day)

Problems to consider when the above are present include:

- Infections (e.g. ear infection, urine infection, meningitis, appendicitis)

- Intestinal pain (e.g. food allergy, acid reflux, constipation, intestinal blockage)

- Trouble breathing (e.g. from a cold, excessive dust, congenital nasal blockage, oversized tongue)

- Increased brain pressure (e.g., hematoma, hydrocephalus)

- Skin pain (e.g. a loose diaper pin, irritated rash, a hair wrapped around a toe)

- Mouth pain (e.g. yeast infection)

- Kidney pain (e.g. blockage of the urinary system)

- Eye pain (e.g. scratched cornea, glaucoma)

- Overdose (e.g. excessive Vitamin D, excessive sodium)

- Others (e.g. migraine headache, heart failure, hyperthyroidism)

Persistently fussy babies with poor weight gain, vomiting more than 5 times a day, or other significant feeding problems should be evaluated for other illnesses (e.g. urinary infection, intestinal obstruction, acid reflux).

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.

Traditionally, nothing by mouth was considered to be mandatory in all cases, but gentle feeding by enteral feeding tube may help to restore motility by triggering the gut's normal feedback signals, so this is the recommended management initially. When the patient has severe, persistent signs that motility is completely disrupted, nasogastric suction and parenteral nutrition may be required until passage is restored. In such cases, continuing aggressive enteral feeding causes a risk of perforating the gut.

Several options are available in the case of paralytic ileus. Most treatment is supportive. If caused by medication, the offending agent is discontinued or reduced. Bowel movements may be stimulated by prescribing lactulose, erythromycin or, in severe cases that are thought to have a neurological component (such as Ogilvie's syndrome), neostigmine. There is also evidence from a systematic review of randomized controlled trials that chewing gum, as a form of 'sham feeding', may stimulate gastrointestinal motility in the post-operative period and reduce the duration of postoperative ileus.

If possible the underlying cause is corrected (e.g. replace electrolytes).

In someone suspected of having cholecystitis, blood tests are performed for markers of inflammation (e.g. complete blood count, C-reactive protein), as well as bilirubin levels in order to assess for bile duct blockage. Complete blood count typically shows an increased white blood count (12,000–15,000/mcL). C-reactive protein is usually elevated although not commonly measured in the United States. Bilirubin levels are often mildly elevated (1–4 mg/dL). If bilirubin levels are more significantly elevated, alternate or additional diagnoses should be considered such as gallstone blocking the common bile duct (common bile duct stone). Less commonly, blood aminotransferases are elevated. The degree of elevation of these laboratory values may depend on the degree of inflammation of the gallbladder.

Biliary sludge is typically diagnosed by CT scan or transabdominal ultrasonography. Endoscopic ultrasonography is another more sensitive option. However, the gold standard is considered to be direct microscopy of aspirated gallbladder bile. This method is much more sensitive, although it is less practical.

Treatment for colitis-X usually does not save the horse. The prognosis is average to poor, and mortality is 90% to 100%. However, treatments are available, and one famous horse that survived colitis-X was U.S. Triple Crown winner Seattle Slew, that survived colitis-X in 1978 and went on to race as a four-year-old.

Large amounts of intravenous fluids are needed to counter the severe dehydration, and electrolyte replacement is often necessary. Flunixin meglumine (Banamine) may help block the effects of toxemia. Mortality rate has been theorized to fall to 75% if treatment is prompt and aggressive, including administration of not only fluids and electrolytes, but also blood plasma, anti-inflammatory and analgesic drugs, and antibiotics. Preventing dehydration is extremely important. Nutrition is also important. Either parenteral or normal feeding can be used to support the stressed metabolism of the sick horse. Finally, the use of probiotics is considered beneficial in the restoration of the normal intestinal flora. The probiotics most often used for this purpose contain "Lactobacillus" and "Bifidobacterium".

Management of colic is generally conservative and involves the reassurance of parents. Calming measures may be used and include: swaddling with the legs flexed, holding the baby on its side or stomach, swinging the baby side to side or back and forth while supporting the head, making a shushing sound, and breast feeding or the use of a pacifier. Eye contact, talking, and holding an infant are also reasonable measures, though is not entirely clear if these actions have any effect beyond placebo.

The differential diagnoses of acute abdomen include but are not limited to:

1. Acute appendicitis

2. Acute peptic ulcer and its complications

3. Acute cholecystitis

4. Acute pancreatitis

5. Acute intestinal ischemia (see section below)

6. Acute diverticulitis

7. Ectopic pregnancy with tubal rupture

8. Ovarian torsion

9. Acute peritonitis (including hollow viscus perforation)

10. Acute ureteric colic

11. Bowel volvulus

12. Bowel obstruction

13. Acute pyelonephritis

14. Adrenal crisis

15. Biliary colic

16. Abdominal aortic aneurysm

17. Familial Mediterranean fever

18. Hemoperitoneum

19. Ruptured spleen

20. Kidney stone

21. Sickle cell anaemia

In humans, enteroliths are rare and may be difficult to distinguish from gall stones. Their chemical composition is diverse, and rarely can a nidus be found. A differential diagnosis of an enterolith requires the enterolith, a normal gallbladder, and a diverticulum.

An enterolith typically forms within a diverticulum. An enterolith formed in a Meckel's diverticulum sometimes is known as a Meckel's enterolith. Improper use of magnesium oxide as a "long-term" laxative has been reported to cause enteroliths and/or medication bezoars.

Most enteroliths are not apparent and cause no complications. However, any complications that do occur are likely to be severe. Of these, bowel obstruction is most common, followed by ileus and perforation. Bowel obstruction and ileus typically occur when a large enterolith is expelled from a diverticulum into the lumen. Perforation typically occurs within the diverticulum.

Most human enteroliths are radiolucent on plain X-rays. They sometimes can be visualized on CT scans without contrast; presence of contrast in the lumen may reveal the enterolith as a void. Most often, they are visualized using ultrasound.

Although recent surveys of enterolith composition are lacking, one early review notes struvite (as in equines), calcium phosphate, and calcium carbonate and reports choleic acid. Deoxycholic acid and cholic acid have also been reported.

At necropsy, edema and hemorrhage in the wall of the large colon and cecum are pronounced, and the intestinal contents are fluid and often blood-stained. Macroscopic and microscopic findings include signs of disseminated intravascular coagulation, necrosis of colonic mucosa and presence of large numbers of bacteria in the devitalized parts of the intestine. Typically, the PCV is >65% even shortly after the onset of clinical signs. The leukogram ranges from normal to neutropenia with a degenerative left shift. Metabolic acidosis and electrolyte disorders are also present. There is leucopenia, initially characterized by neutropenia, which might evolve in neutrophilia. Moreover, haemoconcentration is noted with an increase in the packed cell volume; total proteins are initially increased, but changes into a lower than normal value. The most significant laboratory finding in colitis X is the increase of total cortisol concentration in blood plasma. Histopathologically, the mucosa of the large colon is hemorrhagic, necrotic and covered with fibrohemorrhagic exudate, while the submucosa, the muscular tunic and the local lymphonodes are edematous.

Colic (from Greek κολικός "kolikos", "relative to the colon") or cholic is a form of pain that starts and stops abruptly. It occurs due to muscular contractions of a hollow tube (colon, ureter, gall bladder, etc.) in an attempt to relieve an obstruction by forcing content out. It may be accompanied by vomiting and sweating. Types include:

- Baby colic, a condition, usually in infants, characterized by incessant crying

- Renal colic, a pain in the flank, characteristic of kidney stones

- Biliary colic, blockage by a gallstone of the common bile duct or cystic duct

- Horse colic, a potentially fatal condition experienced by horses, caused by intestinal displacement or blockage

- Devon colic, an affliction caused by lead poisoning

- Painter's colic or lead poisoning

For patients without symptoms, no treatment is recommended. If patients become symptomatic and/or develop complications, cholecystectomy is indicated. For those who are poor surgical candidates, endoscopic sphincterotomy may be performed to reduce the risk of developing pancreatitis.

In simple cases of obstruction, where there are no complications, a variety of non-surgical and surgical techniques are used to remove the enterolith. These include crushing the enterolith and milking it back to the stomach or forward to the colon, surgical removal via an uninvolved segment of the gastrointestinal tract, and resection of the involved segment.

There is considerable research into the causes, diagnosis and treatments for FGIDs. Diet, microbiome, genetics, neuromuscular function and immunological response all interact. Heightened mast cell activation has been proposed to be a common factor among FGIDs, contributing to visceral hypersensitivity as well as epithelial, neuromuscular, and motility dysfunction.

Diagnostic workup varies by the stone type, but in general:

- Clinical history and physical examination

- Imaging studies

- Some stone types (mainly those with substantial calcium content) can be detected on X-ray and CT scan

- Many stone types can be detected by ultrasound

- Factors contributing to stone formation (as in #Etiology) are often tested:

- Laboratory testing can give levels of relevant substances in blood or urine

- Some stones can be directly recovered (at surgery, or when they leave the body spontaneously) and sent to a laboratory for analysis of content