Colic in Horses

Colic in horses is defined as abdominal pain, and can be caused by a wide variety of conditions. Many of these conditions are life threatening, and therefore it is essential to diagnose and treat cases of colic as quickly as possible. The most common causes of colic are gastrointestinal conditions, although it can also be caused by other abdominal conditions. In the latter case, it is often called false colic. Treatment of colic is largely dependent upon identifying the underlying reason for the pain, and treating this cause appropriately. Most commonly this is done medically, but in a small percentage of cases, surgical intervention is needed. Among domesticated horses, colic is a major cause of premature death. The incidence of colic in the general horse population has been estimated between 10 and 20 percent on an annual basis. It is important that any person who owns or works with horses be able to recognize the signs of colic, so that a veterinarian may be called promptly.

Pathophysiology

This can be divided broadly into simple obstructions, strangulating obstructions, and non-strangulating infarctions.

Simple Obstruction

This is characterised by a physical obstruction of the intestine, which can be due to impacted food material, stricture formation, or foreign bodies. The primary pathophysiological abnormality caused by this obstruction is related to the trapping of fluid within the intestine oral to the obstruction. This is due to the large amount of fluid produced in the upper gastro-intestinal tract (around 125L daily), and the fact that this is primarily re-absorbed in parts of the intestine downstream from the obstruction. The first problem with this degree of fluid loss from circulation is one of decreased plasma volume, leading to a reduced cardiac output, and acid-base disturbances.

There also occur serious effects on the intestine itself, which becomes distended due to the trapped fluid, and by gas production from bacteria. It is this distension, and subsequent activation of stretch receptors within the intestinal wall, that leads to the associated pain. With progressive distension of the intestinal wall, there is occlusion of blood vessels, firstly veins, then arteries. The difference in time to onset of occlusion is due to the relatively more rigid walls of arteries compared with veins. This impairment of blood supply leads firstly to hyperaemia and congestion, and ultimately to ischaemic necrosis and cellular death. The poor blood supply also has effects on the vascular endothelium, leading to an increased permeability. This results initially in leakage of plasma, and eventually blood into the intestinal lumen. In the opposite fashion, gram-negative bacteria and endotoxins can enter the bloodstream, leading to further systemic effects.

Strangulating Infarction

Strangulating infarctions have all the same pathological features as a simple obstruction, but the bloody supply is immediately affected. Both arteries and veins may be effected immediately, or progressively as in simple obstruction. Common causes of strangulating obstruction are pedunculated lipomas, and displacement of intestine through a hole, such as a hernia, a mesenteric rent, or the epiploic foramen.

Non-strangulating Infarction

In a non-strangulating infarction, blood supply to a section of intestine is occluded, without any obstruction to ingesta present within the intestinal lumen. The most common cause is infection with Strongylus vulgaris larvae, which develop within the (primarily cranial) mesenteric artery.

Classification

Medical Conditions

Stomach

Food engorgement

This is a life threatening condition, with a great risk of gastric rupture, and also of secondary laminitis. It is caused by excess food intake, for example, a horse that has broken into a food store.

Gastric/pyloric spasm

This commonly affects racehorses, immediately after racing, and is known colloquially as 'racehorse colic'. Typically, the animal will have had access to cold water, but this is not always the case. Although the signs of colic seen may be very violent, this condition is not associated with any risk of gastric rupture. Spasmolytic drugs are ineffective in treatment, however, naso-gastric intubation is immediately curative.

Inappropriate feed/poor mastication

Either of these may lead to a condition where the stomach is unable to efficiently empty. A common example is feeding of unsoaked sugar beet, which then expands within the stomach.

Neurological atony

A chronic motility dysfunction, leading to a slow filling of the stomach with ingesta. Inhibition of gastric outflow is not normally a feature, and therefore gastric rupture is not a risk. A mild colic may be seen, but far more common is poor condition and reduced performance. Warmblood horses are more commonly affected than other breeds, leading to the suggestion that there may be a genetic component to the disorder.

Ulceration

File:Benign gastric ulcer 1.jpg?

A benign gastric ulcer

Equine Gastric Ulcer Syndrome (EGUS) is a common cause of mild to moderate colic, and is more prevalent than had been appreciated. In racehorses, the prevalence is as high as 90%. In other performance horses, prevalence ranges from 40-60%. In foals, prevalence is approximately 25%, and probably higher in those being hospitalized for other reasons.

In adult horses, ulceration commonly occurs in the non-glandular portion of the stomach, unlike in humans, where peptic ulcers are far more common. While the bacterium Helicobacter pylori is a common cause of ulcers in humans, equine gastric ulcers are not typically infectious in origin. It is thought that EGUS is often stress-related, such as after travelling or confinement, and gastric ulceration is a known potential side-effect of treatment with non-steroidal anti-inflammatory drugs. A diet consisting of a high proportion of concentrates is also considered a risk factor. In affected horses, pain is often associated with eating, and the horse typically takes one or two bites of food, then no more. A definitive diagnosis requires endoscopy. Treatment is usually effected using H₂ receptor antagonists, such as Cimetidine, or proton pump inhibitors, such as Omeprazole.

Neoplasia

A malignant squamous carcinoma can effect the cardia and upper squamous regions of the stomach, resulting in a persistent mild colic, commonly seen soon after feeding. Weight loss and general ill health are usually seen, and the prognosis is very poor, due to the high risk of metastasis.

Small Intestine

Spasmodic colic

Spasmodic colic accounts for a large proportion of colic cases seen in first-opinion practice, however, little is known about its causes. It generally produces a mild colic, due to increased peristaltic activity in the gastro-intestinal tract. Cases are usually easily resolved by treating with a spasmolytic such as Buscopan, and a mild analgesic such as phenylbutazone.

Grass sickness

Equine grass sickness, or equine dysautonomia causes a paralysis of the gastro-intestinal tract, by disruption of the autonomic nervous system. This leads to a pooling of ingesta throughout all parts of the gastro-intestinal tract. The condition may occur acutely, or progress chronically over several weeks, but all cases will eventually die. A definitive diagnosis is obtained by taking an ileal biopsy, and inspecting the intrinsic myenteric plexus. There is no effective treatment, although in the short to medium term, horses can be successfully managed by informed and attentive owners.

Caecum

Flatulent colic

Flatulent, or gas colic, occurs when caecal gases are produced faster than they can be removed by the caecum and colon, leading to a distension of the caecum. A diagnosis is strongly confirmed by a right sided abdominal distension, and auscultation/percussion of tympanitic sounds. Treatment involves withdrawal of fluid, and intra-venous fluid therapy. The distension can be relieved by trocharisation of the caecal head, via the right sub-lumbar fossa, which is ideally performed using ultrasound guidance.

Large Colon

Pelvic flexure impaction

A relatively common form of colic, that is often associated with a recent change in diet, management or exercise levels. Pain is moderate, and often persists despite adequate analgesia, a sign more commonly associated with colic of a surgical nature. However, rectal examination provides a definitive diagnosis, with a large, doughy structure occupying much of the pelvis. Treatment involves encouraging fluid output into the large colon, to help soften the impaction, firstly by ensuring adequate hydration with intra-venous fluids, and sometimes by administration of sodium chloride and sodium sulphate orally, to create an osmotic gradient. Large volumes of water, sometimes with Magnesium Sulfate with or without liquid paraffin (Mineral oil) are also given by naso-gastric tube, to help soften the impaction and encourage its movement.

Left dorsal displacement

Left dorsal displacement, or nephrosplenic entrapment, is a frequent cause of colic, where the left dorsal and ventral colon become displaced, and then trapped by the spleen laterally, the kidney medially, and the nephrosplenic ligament ventrally. It can be diagnosed by rectal examination. The first line of treatment is intra-venous phenylephrine injection, which acts to contract the spleen, so helping release the trapped colon. This is often combined with gentle exercise to encourage movement of the abdominal contents. Circling on the left rein is considered particularly helpful, as it increases the potential space between the spleen and the body wall, allowing more room for the colon to return to its normal location. If this fails, then general anaesthesia is needed. Replacement of the colon is then attempted by rolling of the horse. If this also fails then surgery is needed to correct the displacement.

Small Colon

Pelvic masses

A persistent mild colic may be found when intra-pelvic masses impinge upon the gastro-intestinal tract. Most commonly these are haematomas. Peri-anal lesions, such as melanomas may also produce these signs.

Neurological deficits

A complete or partial paralysis of the small colon and rectum may occur with polyneuritis equi, resulting in a lack of faecal expulsion, and consequent obstruction. A diagnosis is made via a neurological examination. Treatment is palliative only, although the condition can be managed for many years by manual emptying of the rectum.

Surgical Conditions

Small Intestine

Impaction

Association with ascarid infection

Intussusception

This is a condition in which one part of the intestine "telescopes" inside another. Usually this obstructs the blood flow to the inner part, and so forms a strangulating obstruction. Intussusception can occur within the small intestine, and also between small intestine and caecum (ileo-caecal intussusception). The latter is predisposed by Anoplocephala perfoliata tapeworm infection. When working up an acute abdominal case, it must be borne in mind that this form of colic is serious and necessitates surgery, however, peritoneal fluid changes will not usually be seen, as will often be found in a surgical colic. This is because the strangulated portion of gut (the inside of the "telescope"), is contained within an intact piece of intestine, so leaking fluid and protein is contained from the peritoneal cavity.

Herniation/entrapment

• Inguinal canal
• Umbilical hernia
• Epiploic foramen
• Mesenteric rents/tears
• Diaphragmatic hernia
• Mesodiverticular bands
• Gastrosplenic ligament

False colic

Signs of colic may be caused by abdominal pain not associated with the gastro-intestinal tract, for example, pain associated with uterine or testicular torsion, or originating from the kidneys, liver, ovaries, spleen, pleuritis, or pleuropneumonia. Other diseases which sometimes cause symptoms which appear similar to colic include laminitis and exertional rhabdomyolysis.

Diagnosis

Many different diagnostic tests can be used to diagnose the cause of equine colic, which may have greater or lesser value in certain situations. The most important distinction to make is whether the condition should be managed medically or surgically. If surgery is indicated, then it must be performed with utmost haste, as delay is a dire prognostic indicator.

History

A thorough history is always taken, including age, sex, recent activity, diet, any recent dietary changes, and routine anthelmintic treatment. However, the most important factor is time elapsed since onset of clinical signs, as this has a profound impact on prognosis, and the type of treatment that will be undertaken.

Cardiovascular Parameters

Heart rate rises with progression of colic, in part due to pain, but mainly due to decreased circulating volume, decreased preload, and endotoxemia. The rate should be measured over time, and its response to analgesic therapy ascertained. A pulse that continues to rise in the face of adequate analgesia is considered a surgical indication. Mucous membrane colour can be assessed to appreciate the severity of haemodynamic compromise. Reddening of membranes reflects worse prognosis, and cyanotic membranes indicate a very poor chance of a positive outcome.

Laboratory tests can be performed to assess the cardiovascular status of the patient. Packed Cell Volume (PCV) is a measure of hydration status, with a value 45% being considered significant. Increasing values over repeated examination are also considered significant. The total protein (TP) of blood may also be measured, as an aid in estimating the amount of protein loss into the intestine. Its value must be interpreted along with the PCV, to take into account the hydration status. Blood lactate levels are useful in determining severity of disease, and as a prognostic indicator; levels between 1-2mmol/L are considered normal, while levels above 5.7mmol/L are considered significant. "Colic scores" that combine several parameters can be relatively accurate prognostic indicators, although most laboratory tests have limited use in terms of specific diagnosis.

Rectal Examination

Repeated rectal examinations are a cornerstone of colic diagnosis, as many large intestinal conditions can be definitively diagnosed by this method alone. Other non-specific findings, such as dilated small intestinal loops, may also be detected, and can play a major part in determining if surgery is necessary.

Naso-gastric Intubation

Passing a Naso-Gastric Tube (NGT) is useful both diagnostically and therapeutically. Fluid is refluxed from the stomach, and any more than 2 litres of fluid is considered to be significant. Increased fluid is generally a result of backing up of fluid through the intestinal tract, due to a downstream obstruction. This finding is important as it represents a relatively advanced stage of colic, and is often a surgical indication. Therapeutically, gastric decompression is important, since horses are unable to vomit. If fluid build up occurs, gastric rupture may occur, which is inevitably fatal.

Abdominocentesis

The extraction of fluid from the peritoneum can be useful in assessing the state of the intestines. A sanguinous fluid can be caused by an infarction, which indicates surgery is necessary. However, sanguinous fluid can also be caused by external trauma (e.g. rib fractures), middle uterine artery rupture in post-foaling mares, or by inadvertent bleeding caused by the procedure itself. A cloudy fluid is suggestive of an increased number of white blood cells, which indicates the disease is relatively advanced. The protein level of abdominal fluid can be analysed, and may also give information as to the integrity of intestinal blood vessels. Elevated lactate levels in the sample can also give an indication of the degree of compromise to bowel, particularly as a peritoneal:peripheral lactate ratio. Peritoneal fluid that contains food material can indicate rupture of the gastro-intestinal tract, although care should be taken that intestine has not been punctured inadvertently. A normal peritoneal fluid sample does not rule out a strangulating lesion. For example, in the case of a diaphragmatic hernia, the strangulating gut is contained within the thoracic cavity, so will not affect fluid within the abdominal cavity. A similar situation is true of intussuception, where the strangulating gut is contained with another piece of non-strangulating gut.

Abdominal Distension

Any degree of abdominal distension is usually indicative of a condition affecting the large intestines, as distension of structures upstream of here would not be large enough to be visible externally.

Auscultation

Auscultation of the abdomen, usually performed in a four quadrant approach, can be a useful tool. Auscultation of the ventral abdomen can also be useful in regions where sand impaction is common. Increased gut sounds are not usually found with major changes, and may be indicative of spasmodic colic, or impending diarrhea. A decreased amount of sound, or no sound, may be suggestive of serious changes. Trapped gas, particularly in the caecum, can often be heard by "pinging", where a flick of the finger against the skin over the affected area causes a sharp sound audible through the stethoscope. This sound is sometimes compared to the ringing sound made by a rubber ball hitting a solid surface.

Faecal Examination

The amount of faeces produced, and its character can be helpful, although as changes often occur relatively distant to the anus, changes may not be seen for some time. In areas where sand colic is known to be common, or if the history suggests it may be a possibility, faeces can be examined for the presence of sand, often by immersion in water, or simply by its texture. The presence of diarrhoea is common in sand colic, and can be seen in horses with enteroliths. Otherwise, diarrhoea is usually indicative of a non-surgical condition, although it can be associated with life threatening conditions such as salmonellosis.

Abdominal Ultrasound

Ultrasonographic evaluation of the abdomen is extremely useful in characterizing certain components of the disease process. The amount and character of free abdominal fluid can be determined, as well as the determination of a specific place for safe, high-yield abdominocentesis. The appearance of small intestine, including distension, wall thickness and motility (or lack thereof, often seen as sedimentatioon of digesta) can be extremely important in the decision for surgical or medical therapy. The large colon and cecum can be evaluated for wall thickness (particularly useful in cases of right dorsal colitis), fluidy contents (colitis/diarrhea), and sometimes displacement. The presence of mesenteric vessels associated with the large colon is generally associated with displacement. The normal anti-mesenteric vessels of the cecum can be used to trace its course. Ventral displacement of the spleen with obscuring of the left kidney is associated with nephro-splenic displacement. Visualization of sacculated large bowel immediately ventral to the liver or spleen, or non-sacculated large bowel in the ventral abdomen suggests displacement. The stomach can be evaluated for distension and abnormalities of the wall. Abdominal ultrasound is useful in detecting diaphragmatic or inguinal herniation. Abnormalities of the liver or kidneys, both potential causes of false colic, are often detectable with ultrasound.

Clinical signs

• Pawing and/or scraping
• Stretching
• Frequent attempts to urinate
• Flank watching
• Pacing
• Repeated flehmen response
• Repeated lying down and rising
• Rolling
• Groaning
• Bruxism
• Excess salivation
• Inappetance
• Decreased faecal output
• Increased pulse rate
• Dark mucous membranes

Epidemiology

Incidence

Colic occurs relatively frequently in horses, with an incidence estimated at 0.1-0.2 episodes per horse-year. In context, this would mean an average holding of 100 horses could reasonably expect to see 10-20 cases every year.

Classification

Approximately 90% of colic episodes can be succesfully managed using medical treatments, with the remainder requiring surgery. Assuming surgical and medical cases of colic are accurately distinguished, survival rates of 95% and 80% are considered normal for medical and surgical colic, respectively.

Post-operative Survival

Studies have shown that there is an increased risk of death with certain factors:

• Abnormal Packed Cell Volume (PCV) on presentation
• Increased length of intestine resected
• Increased duration of surgery
• Elevated peripheral lactate
• Elevated peritoneal fluid lactate

Colic in Horses

See Also

• Equine gastrointestinal anatomy
• Equine nutrition