Colic usually occurs when a section of the intestinal tract is obstructed in such a manner that food cannot be moved along by normal intestinal movements (peristalsis). As a result of this obstruction, gas and fluid accumulate in front of the obstruction leading to distention of that part of the intestine, which then leads to leads to pain. Inserting a balloon into the intestine and inflating it produces colic; this method has been used to test different pain relieving drugs.
A majority of cases of colic are associated with changes in the diet. For example, if a horse eats a lot of dry hay and fails to drink sufficient water, signs of colic occur as a result of simple constipation ("impaction"). There are many different causes of colic – most are associated with dietary factors.
The design of the equine intestinal tract is such that it is surprising that colic is not observed more frequently than it is. Although colic occurs rarely in wild horses, the constraints imposed by the necessities of human management (confinement and feeding) have made colic one of the most common medical problems with which domesticated horses are faced. The equine intestinal tract is very complex (compared with that of human beings and dogs). This complexity arose through evolution in conjunction with the fact that the horse, in its natural environment, roams the grasslands and depends solely on a diet of grass.
Like other herbivores, horses do not produce the enzymes necessary for the digestion of grass (hay). In order to obtain nutrients from grass, the horse's intestinal system serves to accommodate a large population of microorganisms that are capable of digesting grass, making those nutrients available to their host (the horse). The relationship between the horse and its intestinal microorganisms ("flora") is referred to as symbiosis. The large intestine of the horse functions in a similar manner to the bovine rumen, a series of fermentation chambers.
Through evolution, the symbiotic relationship between the horse and its flora depends on a uniform diet. Diet changes lead to changes in the flora and changes in the flora may adversely affect the horse's intestinal system. If the normal flora is presented with a changing variety of substrates (food) there will be changes in the make-up of the microbial population that may or may not not be significant. The microbial population is enormously adaptable and is able to adjust to many types of diet and changes in diet. However, if a diet change is sudden and/or involves a major contrast between dietary compositions, it is likely that the normal flora will be adversely affected and may result in a variety of problems (alteration in motility patterns or increased gas accumulation). The most common clinical manifestation of floral imbalance is colic.
It is therefore always recommended that any anticipated diet changes are made gradually so that the normal flora can adapt and not become overwhelmed. If the colonic flora is adversely changed beyond its ability to compensate, a number of adverse effects may arise, including: increased gas production, synthesis of toxins, and perturbation of normal intestinal motility (peristalsis).
Other factors that have been identified as increasing the risk for colic include parasite damage to the intestine, insufficient exercise, insufficient water consumption, ingestion of sand or soil (geosediment), and the effects of fear or apprehension. A substantial number of horses develop colic following thunder storms. It is believed that this association may represent an effect of fear or worry. Although much less common, numerous conditions of the intestine itself, including cancer and infections, may also lead to colic.
What is the Difference Between "True" Colic and "False" Colic?
The behavioral manifestations of colic are further classified based on the underlying cause. "Colic" presentations may be subdivided into true colics and false colic. True colic represents the situation in which the abnormal behavior is directly attributed to obstruction of the intestinal tract. False colic refers to the situation in which the behavioral abnormalities are associated with a non-intestinal problem. Some "diseases" that produce colic symptoms but are not associated with the intestinal tract include: Normal foaling
Dystocia (difficult foaling)
Broad ligament hematoma (middle uterine artery rupture)
Retention of placental membranes
Exertional rhabdomyolysis ("tying-up")
Polysaccharide storage myopathy (PSSM)
Pheochromocytoma – tumor of the adrenal gland (peri-renal hemorrhage)
Encephalomyelitis (e.g., rabies)
Esophageal obstruction ("choke")
Hypocalcemia in the mare
Pus-distension of the scrotum following castration
Hepatitis (liver pain and encephalopathy)
Hyperkalemic periodic paralysis
Heavy metal toxicity
Rupture of the prepubic tendon
Extensive abdominal neoplasia
These conditions should be considered when a colic case is examined: they may give rise to clinical signs (behavior) which are properly described as colic or may which may also be causing some actual abdominal pain. The term "true colic" is reserved for those obstructive afflictions of the alimentary tract which cause manifestations of abdominal pain.
Whenever a simple colic (such as an impaction) is left untreated, there exists a risk that the intestine may become twisted within the abdomen. Twisting of the intestine represents an emergency situation for which surgical treatment is often needed.
A typical situation that commonly leads to twisting of the intestine involves the development of a simple colic during the evening time after the horse has been fed and checked for the last time. If colic subsequently develops during the night and is not recognized, the horse's attempts to roll may lead to the intestine turning on itself within the abdomen. Risk of twisting is increased by the presence of both extra gas and a heavy impaction. The combination of gas and an impaction act together to destabilize the intestine such that, when the horse rolls (response to pain) the whole intestine may turn on itself.
The presence of a twist adds to the obstruction. In many cases, the presence of a twist also leads to blockage of the intestinal blood supply and causes the affected part of the intestine to die. Twisting of the intestine is therefore very serious and, for successful treatment, requires early recognition and hospitalized care (including surgery).