Colic in horses is defined as abdominal pain, but it is a clinical sign rather than a diagnosis. The term colic can encompass all forms of gastrointestinal conditions which cause pain as well as other causes of abdominal pain not involving the gastrointestinal tract. The most common forms of colic are gastrointestinal in nature and are most often related to colonic disturbance. There are a variety of different causes of colic, some of which can prove fatal without surgical intervention. Colic surgery is usually an expensive procedure as it is major abdominal surgery, often with intensive aftercare. Among domesticated horses, colic is the leading cause of premature death. The incidence of colic in the general horse population has been estimated between 10 and 11 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 and determine whether or not a veterinarian should be called.
This list of types of colic is not exhaustive but details some of the types which may be encountered.
Pelvic flexure impaction
This is caused by an impaction of food material (Water, Grass, Hay, Grain) at a part of the large bowel known as the pelvic flexure of the left colon where the intestine takes a 180 degree turn and narrows. Impaction generally responds well to medical treatment, but more severe cases may not recover without surgery. If left untreated, severe impaction colic can be fatal. The most common cause is when the horse is on box rest and/or consumes large volumes of straw, or the horse has dental disease and is unable to masticate properly. This condition could be diagnosed on rectal examination by a veterinarian.
Spasmodic colic is the result of increased peristaltic contractions in the horse's gastrointestinal tract. It can be the result of a mild gas buildup within the horse's digestive tract. The signs of colic are generally mild and respond well to spasmolytic and analgesic medication.
The ileum is the last part of the small intestine that ends in the cecum. Ileal impaction can be caused by obstruction of ingesta. Other causes can be obstruction by ascarids (Parascaris equorum) or tapeworm (Anoplocephala Perfoliata) as mentioned below.
This is most likely to occur in horses that graze sandy or heavily grazed pastures leaving only dirt to ingest. The term sand also encompasses dirt. The ingested sand or dirt accumulates in the pelvic flexure, right dorsal colon and the cecum of the large intestines. As the sand or dirt irritates the lining of the bowel it can cause diarrhea. The weight and abrasion of the sand or dirt causes the bowel wall to become inflamed and can cause a reduction in colonic motility and in severe cases even peritonitis. Historically medical treatment of the problem is with laxatives such as liquid paraffin or oil and psyllium husk. More recently doctors are treating cases with specific synbiotic (pro and prebiotic) and psyllium combinations. Some cases may need surgery. Horses with sand or dirt impaction are predisposed to Salmonella infection. Horses should not be fed from the ground in areas where sand, dirt and silt are prevalent although small amounts of sand or dirt will still be ingested by grazing. Management to reduce sand intake and prophylactic treatments with sand removal products are recommended by most veterinarians.
Enteroliths in horses are round balls of mineral deposits often formed around a piece of ingested foreign material, such as sand or gravel. When they move from their original site they can obstruct the intestine. Enteroliths are not a common cause of colic, but are known to have a higher prevalence in states with a sandy soil and where an abundance of alfalfa hay is fed, such as California. Once a horse is diagnosed with colic due to enterolith it usually requires surgery to correct the condition.
Occasionally there can be an obstruction by large numbers of roundworms. This is most commonly seen in young horses as a result of a very heavy infestation of Parascaris equorum that can subsequently cause a blockage and rupture of the small intestine. Deworming heavily infected horses may cause a severe immune reaction to the dead worms, which can damage the intestinal wall and cause a fatal peritonitis. Veterinarians often treat horses with suspected heavy worm burdens with corticosteroids to reduce the inflammatory response to the dead worms. Blockages of the small intestine, particularly the ileum, can occur with Parascaris equorum and may well require colic surgery. Large roundworm infestations are often the result of a poor deworming program. Horses develop immunity to parascarids between 6 months age and one year and so this condition is rare in adult horses.
Tapeworms at the junction of the cecum have been implicated in causing colic. The most common species of tapeworm in the equine is Anoplocephala perfoliata. However, a 2008 study in Canada indicated that there is no connection between tapeworms and colic, contradicting studies performed in the UK.
Acute diarrhoea can be caused by cyathostomes or "small Stronglus type" worms that are encysted as larvae in the bowel wall, particularly if large numbers emerge simultaneously. The disease most frequently occurs in winter time. Pathological changes of the bowel reveal a typical "pepper and salt" colour of the large intestines. Animals suffering from cyathostominosis usually have a poor deworming history. There is now a lot of resistance to fenbendazole in the UK.
Left dorsal displacement
Left dorsal displacement is a form of colic where the left dorsal colon becomes trapped above the spleen and against the nephrosplenic ligament. It may necessitate surgery although often it can be treated with exercise and/or phenylephrine, at times anesthesia and a rolling procedure[clarification needed] must be performed to correct the condition medically. This condition can be diagnosed on rectal examination or through ultrasonography by a veterinarian.
Right dorsal displacement
Right dorsal displacement is another displacement of part of the large bowel. Although signs of colic may not be very severe, surgery is usually the only available treatment.
Various parts of the horse's gastrointestinal tract may twist upon themselves. It is most likely to be either small intestine or part of the colon. Occlusion of the blood supply means that it is a painful condition causing rapid deterioration and requiring emergency surgery.
Intussusception is a form of colic in which a piece of intestine "telescopes" within a portion of itself. It most commonly happens in the small intestine of young horses and requires urgent surgery.
Epiploic foramen entrapment
On rare occasions, a piece of small intestine can become trapped through the epiploic foramen. The blood supply to this piece of intestine is immediately occluded. The intestine becomes trapped and surgery is the only available treatment.
Benign fatty tumors known as lipomas can form on the mesentery. As the tumor enlarges, it stretches the connective tissue into a stalk which can wrap around a segment of bowel, typically small intestine, cutting off its blood supply. The tumor forms a button that latches onto the stalk of the tumor, locking it on place, and requiring surgery for resolution.
Mesenteric rent entrapment
The mesentery is a thin sheet attached to the entire length of intestine, enclosing blood vessels, lymph nodes, and nerves. Occasionally, a small rent (hole) can form in the mesentery, through which a segment of bowel can occasionally enter. As in epiploic foramen entrapment, the bowel first enlarges, since arteries do not occlude as easily as veins, which causes edema (fluid buildup). As the bowel enlarges, it becomes less and less likely to be able to exit the site of entrapment. This problem also requires surgical correction.
Horses form ulcers in the stomach fairly commonly. Risk factors include confinement, infrequent feedings, a high proportion of concentrate feeds[clarification needed], excessive non-steroidal anti-inflammatory drug use, and the stress of shipping and showing. Most ulcers are treatable with medications that inhibit the acid producing cells of the stomach. Antacids are less effective in horses than in humans, because horses produce stomach acid almost constantly, while humans produce acid mainly when eating. Dietary management is critical. Bleeding ulcers leading to stomach rupture are rare.
Other causes that may show clinical symptoms of colic
Strictly speaking colic refers only to signs originating from the gastrointestinal tract of the horse. Signs of colic may be caused by problems other than the GI-tract e.g. problems in the kidneys, ovaries, spleen, testicular torsion, pleuritis, or pleuropneumonia. Diseases which sometimes cause symptoms which appear similar to colic include laminitis and exertional rhabdomyolysis.
Pathophysiology of equine colic
This can be divided broadly into simple obstructions, strangulating obstructions, and non-strangulating infarctions.
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[clarification needed]), 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 obstructions have all the same pathological features as a simple obstruction, but the blood supply is immediately affected. Both arteries and veins may be affected immediately, or progressively as in simple obstruction. Common causes of strangulating obstruction are intussusceptions, volvulus and displacement of intestine through a hole, such as a hernia, a mesenteric rent, or the epiploic foramen.
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.
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.
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.
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.
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.
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 as 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, as if fluid build up occurs, gastric rupture may occur, which is inevitably fatal.
The extraction of fluid from the peritoneum can be useful in assessing the state of the intestines. A sanguinous fluid represents an infarction, and usually indicates surgery is necessary. 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.
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 of the abdomen, usually performed in a four quadrant approach, can be a useful tool. Increased gut sounds are not usually found with major changes, and may be indicative of spasmodic colic. A decreased amount of sound, or no sound, may be suggestive of serious changes.
The amount of feces 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.
- Pawing and/or scraping
- Frequent attempts to urinate
- Flank watching: turning of the head to watch the stomach and/or hind quarters
- Biting/nipping the stomach
- Repeated flehmen response
- Repeated lying down and rising
- Excess salivation
- Loss of appetite
- Decreased fecal output
- Increased pulse rate
- Dark mucous membranes
The incidence of colic can be reduced by restricted access to simple carbohydrates, providing clean feed and drinking water, preventing the ingestion of dirt or sand by using an elevated feeding surface, a regular feeding schedule, regular deworming, regular dental care, a regular diet that does not change substantially in content or proportion and prevention of heatstroke. Horses that bolt their feed are at risk of colic, and several management techniques may be used to slow down the rate of feed consumption.
Turnout is thought to reduce the likelihood of colic, although this has not yet been proven. It is recommended that a horse receive ideally 18 hours of grazing time each day, as in the wild, although many times this is difficult to manage with competition horses and those that are boarded, as well as for animals that are easy keepers with access to lush pasture and hence at risk of laminitis. Turnout on a dry lot with lower-quality fodder may have similar beneficial effects
- The Illustrated Veterinary Encyclopedia for Horsemen Equine Research Inc.
- Veterinary Medications and Treatments for Horsemen Equine Research Inc.
- Horse Owner's Veterinary Handbook James M. Giffin, M.D. and Tom Gore, D.V.M.
- Preventing Colic in Horses Christine King, BVSc, MACVSc
-  Vet advice: Colic in horses
- ↑ Stephen, Jennifer (2009). The horse professional guide to colic. www.horseprofessional.com
- ↑ Oke, Stacy. "Research Ongoing for Tapeworm, Colic Link." The Horse July 2008: 20.
- ↑ K.J. Chandler, M.C.Collins, S.Love. Efficacy of a five-day course of fenbendazole in benzimidazole- resistant cyathostomes.Veterinary Record (2000) 147, 661-662.
- ↑ 4.0 4.1 Blikslager, Anthony. "Avoiding Colic Through Management." The Horse July 2008: 47-54.