Causes. Certain anatomical and physiological conditions contribute to this disease in the horse. The ingesta as it leaves the stomach is liquid or pultaceous and throughout the small intestines it remains so, so that they are little liable to impaction. But by the time the cæcum is reached much of the liquid has been absorbed, and as the contents pass into the double colon they are usually a soft solid, which gradually becomes dried as it advances through the double and floating colon. The sacculation of cæcum and colon tends to delay the masses and favors absorption. The pelvic flexure, the narrowest part of the double colon, is formed by an acute bend of the viscus on itself so that the dried masses advancing from in front are especially liable to become arrested and impacted at this point. Impaction may, however, occur at any part of the large intestine.
Any debility or atony of the intestines predisposes to the condition. The ingesta accumulates in the portion which does not contract sufficiently to pass it onward, and this soon becomes distended to a state of absolute paresis. All conditions of debility, and all prolonged ill health tend to operate in this way by lessening vermicular movement.
Again in cases of nausea or intestinal disorder the supervention of antiperistaltic movements, will tend to accumulate the ingesta at one point and favor impaction (Ernst).
As in the case of other indigestions the imperfect preparation of the food is an active factor. Diseased teeth, jaws or salivary glands, act in this way and a functionally weak stomach contributes to this as to other intestinal disorders.
An excess of food and especially indigestible food will contribute to impaction. Heating grain, like corn, wheat, buckwheat, passed rapidly through the stomach in an imperfectly digested condition, tends to accumulate in the larger intestines. Hard, fibrous fodders like hay and straw that have run to seed, or which have been washed out by rains, bleached or heated, rye-straw, the stalks of beans, peas, vetches, which have been similarly spoiled, and clover hay affected with cryptogams or other ferments act in the same way. Even clover eaten green, produces in foals impactions to which the hairs of the leaves and chalices materially contribute (Verrier). The allied plants alfalfa and sainfoin when passed rapidly through the stomach tend to impaction of the large intestines. But any fibrous, indigestible and innutritious fodder, taken in excess to make up the deficiency of nutriment is liable to act in this way.
Other conditions that contribute to impaction are lack of water, especially at night when much hay is consumed, and lack of exercise which tends to torpor of both liver and bowels.
Finally verminous aneurisms and embolism of the intestinal arteries induce congestion, paresis, spasms, and other disorders which tend to aggregation and impaction. Also tumors, strictures and obstructions of all kinds tend to impaction.
Symptoms. A certain amount of impaction is not incompatible with ordinary health, but as this increases all grades of colic may be met with from the most simple and transient to the most persistent and severe.
In the milder forms slight and transient colics come on after meals, for days in succession, before any serious attack is sustained. These are especially marked under dry bulky fodder (hay), less so on grain, and less on green food or roots. The animal paws, moves the hind limbs uneasily, looks at the flanks, he may even kick at the abdomen, lie down and roll, rise, pass a little manure or flatus, and seeming relieved may resume feeding, until the next attack. The intermissions may last a few minutes, a quarter of an hour or longer, and they gradually become more prolonged until they disappear for the time. Sooner or later, however, the obstruction becomes more complete and the colic more severe and persistent. To the ordinary symptoms of violent abdominal pain there are added symptoms which point to bowel impaction or obstruction. There is a special tension of the right side of the abdomen, with flatness on percussion. When down there is a tendency to sit on the haunches to relieve pressure on the diaphragm and lungs. When standing there is a disposition to stretch the fore limbs out forward and the hind ones backward. Fæces may be passed at first in a few small round balls at a time, but this soon ceases, and very little or none can be obtained even by the use of enemas. The straining is usually so violent as to expel the enemata as soon as introduced. The hand introduced into the rectum can easily detect the solid impacted pelvic flexure of the colon pressing backward into the pelvis or impinging on the right pubis. Another common symptom is the frequent passage of urine in dribblets, due to the irritation of the bladder by the pressure upon it of the impacted colon during straining. In cases of this kind the colon and cæcum become tympanitic as first shown by a resonant distension of the right flank obliterating the hollow in front of the ilium, and later by a similar condition of the left flank.
The abdominal pain is usually less acute than in simple spasmodic colic or intestinal congestion. The face is less pinched and anxious, the eye less frightened, the kicking at the belly less violent, and the lying down more deliberate and careful. Very commonly the patient merely rests on his belly or side without attempting to roll.