The term colic refers to pain in the abdomen of horses. It is not a single disease, but is the manifestation of a considerable number of diseases: all of which produce pain, and some of which are potentially deadly. Making a specific diagnosis to determine the actual cause of the colic can be extremely difficult for veterinarians at times.
Because of the multitude of possible causes, it is of value to examine several excellent recent research reviews which looked closely at the classification of colics, and at the causative factors, incidence and mortality associated with these diseases.
The majority of cases of colic occur due to unknown causes, but are primarily presumed to be associated with intestinal muscle spasm or the accumulation of abnormal amounts of gas in a portion of the intestine. In general, colic results due to the distension of the bowel by ingesta, fluid, gas, or due to a functional impairment of the normal intestinal motility. In more severe cases, abdominal pain may be the result of damage to the intestinal wall by reduced blood supply (ischaemia), inflammation, death of tissue (infarction) or oedema (swelling and increased fluid).
The causes of colic can be classified by well recognised pathological categories, including obstruction, strangulation, enteritis/colitis, peritonitis, as well as by the site involved – stomach, small intestine, caecum, large colon, small colon, peritoneum, and other organs including liver, spleen and kidney Rather than simply listing the types of colic which can occur, it is now of value to look at what we do actually know about causes, prevalence and risk factors, as well as strategies to prevent colics.
Nathaniel White, DVM, of the Marion Dupont Scott Equine Medical Center, Virginia, reviewed the risk factors in the USA in 2002, in his publication “Prevalence, demographics and Risk Factors for Colic, www. ivis. org, with the following comments and observations; Out of 100 horses in the general population, 4-10 cases of colic are expected in one year. About 10-15% of the colics are repeat cases, with some horses having 2-4 colic episodes yearly. Horses that have had a previous colic are three times as likely to have a second colic compared to a horse that has never had colic.
Most colic signs were simple colic or ileus (no contractions of the gut) with no specific diagnosis entered in 80-85% of cases. In one study, 30% of horses with colic were identified by owners but never seen by vets because the colic was short lived or resolved by the owner. Studies of colic cases seen by vets reported a predominance of simple obstruction or spasmodic colic. Impaction colics made up about 10% of cases, and obstruction or strangulating diseases requiring surgery made up from 2-4% of cases.
Universities report that simple colic and impaction colics are the most commonly reported. When a specific gut location can be identified by veterinarians, the large colon is the most commonly affected, followed by small intestine, caecum and small colon respectively. Diseases which cause strangulation (twisted bowel) have the highest fatality rate- with the large colon torsions being more common than small intestine torsions. Colic is responsible for more deaths in horses than any other disease except old age.
In normal farm horse populations, horse mortality from all types of colic was 0. 7 deaths per 100 horse-years, with a colic case fatality rate of 6. 7%. Risk Factors For Colic In some colic cases the cause may be evident, such as in grain overload, but even in these cases, the exact mechanism which initiates the problem is often unknown. By looking at known risk factors we can begin to reduce the incidence by eliminating possible risk factors. There are internal and external risk factors for colic: Breed
While no breed is immune to colic, several studies suggest that Arabian horses have more colic episodes, while some other studies suggest that Thoroughbreds have more. Standardbreds and Warmbloods tend to have more inguinal hernias due to the increased size of their inguinal ring. Age Young and older horses appear to be less at risk of simple colic, so middle aged horses are most at risk. Weanlings and yearlings are most likely to suffer ileocaecal intussusceptions. Diet Diet has long been blamed for colic.
Course roughage with low digestibility or particularly coarse fibre is observed to cause impaction colic. Grain overload significantly increases the risk of colic and laminitis. Feeds such as lush clover and lush pasture have been implicated in causing bloat. Information on feeding here When investigated by controlled studies, increased amounts of grain, and changes in the type of hay and grain fed during the year both increased the odds of colic compared to horses without grain or changes in feed. One study also reported that daily feeding of concentrate from 2. to 5kg/day and >5kg/day to adult horses increased the risk of colic by 4. 8 and 6. 3 times respectively, compared to horses fed no concentrate. Interestingly, controlled studies confirm that pellet feeds and sweet feeds were associated with an increased risk of colic compared to no grain fed or single grain diets. Grain diets are also known to decrease the water content in the colon contents due to a decrease in fibre which binds to water in the colon. Grain diets are also known to travel through the stomach much more rapidly than fibrous diets.
Grain in the diet increases gas production, and is much more likely to produce an environment needed for bloat and intestinal displacements. The horse stomach is relatively small, and is designed to take in small quantities of food often. Horses are herbivores, and naturally spend a large part of the day grazing, continually taking in small quantities of food. When more intensive management, including work and training programs, stabling, and feeding 2-3 times daily, occurs, the normal feeding habits of horses are disrupted to varying degrees.
Intensive stabling and work often require higher energy levels in feedstuffs to allow the horse to cope with increased work requirements. The higher energy levels are provided by high grain and concentrate components in the ration, often at the risk of reducing roughage and fibre levels to inadequate volumes. The horse digestive system is designed to utilise roughage and fibre, and any deficiency of fibre will result in digestive disturbances, including colics. It is highly important to continue regular feeding habits of horses, maintaining regular feed volumes and feeding intervals.
Do not work horses hard after a full feed. Never give large quantities of food to a horse not accustomed to it. Make feeding changes gradually. Do not allow an overheated horse to drink cold water until it has cooled off sufficiently, or the cold water will almost certainly predispose the horse to colic. Water horses before feeding. Allow access to water again immediately after feeding. Horses prefer clean, fresh water available at all times. A horse will drink anywhere from 22 to 68 litres of water daily, depending on weather conditions, diet and workload.
Do not feed horses directly off the ground, especially in sandy or fine gravel regions, as the uptake of sand will predispose horses to sand colics and impactions. Avoid sudden feed changes. These will rapidly induce colic in most horses. Mouldy feeds, such as hay, are potentially deadly to horses, and regularly cause colic. Check hay thoroughly, especially any lush, moist hay which may have been baled while too wet. Never feed mouldy hay to horses. Environment & Management Housing and confinement on farms in the Virginia study were not risk factors for colic.
It does however seem logical that changes in diet or feeding routine are associated with risk of colic. Certainly large horse properties report that the routine of feeding grain after being brought in from pasture to stables increases the colic risk – specifically for bloat and displacements. Altering this routine by keeping horses turned out after feeding grain decreases the rate of colic. Similarly, when hay is available to horses on lush pasture, the hay will be consumed as part of the diet and colic rate is decreased.
Sand colic and impactions are seen where horses graze on pastures grown on sandy soils, or where horses are forced to eat off the ground with predominantly sand or fine gravel. Previous colic Horses with a history of colic are at higher risk for more colic episodes Parasites Internal parasites are related to increased colic risks in many studies. Gut obstructions due to ascarids in foals, tapeworm related colic and strongyle infections have all been reported as causing colics. Many reports confirm a decrease in colic after controlling small strongyle infections on properties with previously high colic incidences.
Tapeworm infestations have been related to increased colic, specifically with colic associated with diseases of the ileum and caecum including increasing the rate of serious intussusception at the ileocaecal region. The general use of ivermectin over the last 20 years has seen a reduction in reports of colic associated with thrombosis of the cranial mesenteric artery due to Strongylus vulgaris larvae. Pregnancy Mares are reported to have a higher risk of colic by colon displacement during late pregnancy and lactation, particularly from 60 to 150 days after foaling.
The actual reasons for this are not known, but calcium levels and alterations in diet including increases in energy due to the higher levels of concentrates in the diet to support lactation may be related to the increased risk. Exercise Racehorses, event horses and endurance horses all have an increased risk of gastric ulceration which can be linked to some colic episodes. These horses are often on high grain/low roughage diets which tend to produce gut acidosis and predispose to colics. Transport and Traveling Transport increases the risk of colic in several studies.
Many vets commonly administer a laxative to horses prior to transport to prevent colic from impactions. These colics may be due to variations in feeding routine, fluid intake, dehydration, etc. Weather Many veterinarians frequently associate weather changes with increased frequency of colic, but many studies can find no confirmation of this. Prognosis and Strategies to Prevent Colic In a second paper, “Prognosis and Strategies to Prevent Colic”, Nathaniel White discussed the survival issues with colic cases, stating that predicting survival in horses with colic is often challenging.
Any horse which does not respond to initial therapy may be regarded as having a much more serious prognosis. In an effort to assist veterinary practitioners and owners, White attempted to apply previous knowledge of outcomes for specific diseases. Case fatality for specific colic diseases varies from a few deaths in cases of simple colic to as much as 75% in some forms of strangulated intestine. Simple obstructions of the large colon such as displacements and impactions have low fatality rates (<10%) whereas simple obstructions or impactions of the small intestine are somewhat higher at up to 30%.
In recent years reports of fatalities to colic have changed with earlier horse referral to veterinary surgeries, improved surgical techniques, better anesthesia, and much improved critical care of surgical patients. A recent report states short term fatality of small intestinal strangulation has decreased from 75% in 1983 to 25% in 2000. The likelihood of fatality following successful surgery is highest in the 10 days after surgery and discharge. Prevention of Colic Consider two factors when trying to prevent colic; (a) Farm factors (b) Horse factors
Farm factors include management, use, feeding and environment. The associated risks on properties with high rates of colic include poor parasite control, high concentrate levels in the diet, multiple sources of concentrate feeds – including supplements with high levels of soluble carbohydrates, chronic water deficiency, excessive use of NSAID’s (non-steroidal anti-inflammatory agents such as phenylbutazone), rapid changes in hay or grain diet, and horses in work that are fed large amounts of carbohydrate and reduced amounts of roughage.
Based on these known factors, colic prevention should start by ensuring horses have a constant fresh water source, ensure that forage makes up at least 60% or more of the diet (horse digestion is designed to utilise forage, not concentrates), and that concentrates (soluble carbohydrates) are fed at the minimal level required to maintain weight and performance. Changes in feed should be completed over a 7-10 day period, and parasite control must be regular and effective.
If you have a property with a high incidence of colics, careful monitoring of the daily management, plus close measurement of energy, protein and fibre in the diet should be urgent steps in reducing colic incidence. It would be extremely valuable to have an independent dietary evaluation conducted to confirm that the diets you are feeding are applicable and adequate, as carbohydrate overloads are much more common than most people would consider. Many owners do not consider, for example, that bran can have a very high soluble carbohydrate content.
If bran is fed simply as a laxative in a regular grain diet, the soluble carbohydrate level in a horse’s diet can rapidly be doubled to dangerous levels. Other known factors which affect individual horses include confinement due to injury, lack of opportunity to turn out and graze/exercise, gastric ulceration, crib biting and excessive air intake during similar vices. These issues are often related to simple colics. Some difficult horses may only respond to being on pasture 24 hours a day with a total forage diet, and this arrangement may not fit in with demands for performance.
A 1999 publication by Cohen, Gibbs and Woods: “Dietary and Other Management Factors Associated with Equine Colic”, AAEP Proceedings 1999, Vol. 45:pp96 investigated the association of dietary changes with colic by asking veterinarians. The following factors in this study were associated with increased risk of colic: Recent changes in diet, Recent changes in type of hay History of previous colic Recent change in weather conditions Recent change in stabling Arabian breed Use of an anthelmintic in previous 7 days Failure to regularly deworm Age over 10 years
Regular exercise (versus pastured at all times). The finding that a change in diet during the 2 week period when colic occurred is a consistent finding with other studies. Often, a change in the specific type of hay was the only dietary change (hay of poorer quality is often less digestible, thereby predisposing to colic impactions. It is also possible that changes in hay cause alterations pH levels in the colon, volatile fatty acid production, and even in the microflora populations in the large intestine, predisposing the horse to disorders of intestinal function resulting in colic).
Colic was regularly associated with recent deworming, irrespective of the product used. In foals, recent deworming may cause colic associated with intestinal obstruction resulting from rapid death of ascarids in the gut, as well as with hatching of large numbers of larval cyathostomes (small strongyles) from cysts in the gut wall after deworming kills all adults in the gut. Recent changes in stabling were frequently associated with increased colics in this study