A large proportion of the cases have been found in horses that have died of colic, or which have been cast for operation, and the recent character of the lesions has often shown that we must look upon them as the result of the tumultuous peristalsis, and the lying, rolling, sitting and other sudden and unwonted movements performed. A heavily loaded portion of bowel, occupying a position slightly lower than a lighter portion or parallel to it, suddenly moves by gravitation when their relative positions are altered as in rolling, decubitus, or rising, and it thereby becomes twisted upon itself. Or a portion of intestine filled with liquid or gaseous contents is suddenly emptied by the passage of these onward into another and the latter portion of intestine or some other lodged alongside it, in moving to fill the place, rotates upon itself and establishes a volvulus.
Hard worked horses which are subjected to stimulating feeding are much more frequently attacked than those which have light work and feeding. In the same way newly harvested hay or oats, spoiled or otherwise indigestible food have apparently been productive causes. Cold drinks, and exposure to cold draughts have been similarly charged. Indeed any cause of indigestion and colic may be held to predispose to volvulus.
Lesions. Seat. Twisting of the small intestine is impossible in the duodenum, and for the floating portion it is far more common in the ileum and terminal portion of the jejunum where the mesentery is long than in the anterior jejunum where it is short.
The double colon from the sternal portion to the pelvic flexure being free from any restraint by omental or mesenteric bands is especially liable to torsion. Palat found four cases of torsion of the colon to one of the small intestine, and Schutze gives the ratio as 56 of the first to 13 of the second.
The cæcum has been frequently found twisted upon itself with a portion of the small intestine rolled round it.
The floating colon like the small intestine is rolled around its mesenteric axis, but cases are much more rare than in the case of the small intestine.
In a recent and complete twisting with obstruction of the bowel, the loop of intestine is distended with gas the result of fermentation of its contents, and its walls may be thin and pale. Much more commonly and when the lesion is of longer standing there is hyperæmia, and infiltration and thickening with inflammatory products, and blood extravasations. At the seat of torsion the compressed intestine is congested, covered with petechiæ, and its peritoneal surface with fibrinous exudate tending to bind the parts together. Later there may be seen spots of necrosis and perforating sores and semi-detached sloughs, or the whole mass of twisted bowel may be gangrenous. The patient usually dies before this last stage has been reached. If the animal survives long enough the lesions of infective peritonitis are constantly present.
Symptoms. The disease usually sets in suddenly with intense severity. In exceptional cases there is an insidious onset, the twist being at first but partial and gradually increasing and for a time the contents pass on in a restricted but still physiological manner. Colics at first slight become by degrees more and more intense until all the symptoms of obstruction and acute inflammation are developed.
More commonly symptoms of extreme gravity appear at once, the patient stops, paws, kicks at his belly, tries to lie down, strains to defecate or urinate, lies down, rolls, sits, gets up and moves round uneasily trying to lie down again. He looks at the flank with anxious eye and countenance and has all indications of the most violent colic. Pain is constant, but worse at one time than another, the pulse is from 50 to 90 and becomes weak and even imperceptible as the case advances, and hyperthermia, at first slight or absent rises with the onset of inflammation. Finally great prostration, depression and stupor, sunken, glazed eye with dilated pupil, and cold sweats and extremities bespeak collapse or general infection.
Diagnosis is rarely certain. The sudden onset, extreme violence of the symptoms, and rapidly fatal progress are significant and in exceptional cases rectal exploration will detect obstruction in the rectum or floating colon, or a tympanitic condition of the pelvic flexure.