Causes. Overloading of the rumen is especially common as the result of a sudden access to rich or tempting food to which the animal has been unaccustomed. Accidental admittance to the cornbin, breaking into a field of rich grass, clover, alfalfa, corn, sorghum, vetches, tares, beans, peas, or grain, or into a barrel of potatoes or apples will illustrate the common run of causes. A pre-existing or accompanying torpor or paresis of the stomach is a most efficient concurrent cause, hence the affection is especially common in animals debilitated by disease or starvation, but which have become convalescent or have been suddenly exposed to the temptation of rich food. For the same reason it is most likely to occur with food which contains a paralyzing element, as in the case of the following when they have gone to seed but are not yet fully ripened: Rye grass, intoxicating rye grass, millet, Hungarian grass, vetches, tares and other leguminosæ, and to a less extent, wheat, barley, oats and Indian corn. The same may come from the paralyzing products of fungi or bacteria in musty fodder or of such chemical poisons as lead, and the cyanides.
A catarrhal affection of the rumen, and the congestion produced by irritant plants, green food with an excess of chlorophyll, and the whole list of irritants and narcotico-acrids, will weaken the first stomach and predispose to overdistension.
Anything which lessens the normal vermicular movements of the rumen and hinders regurgitation and rumination tends to impaction, and hence an aliment which is to a large extent fibrous, innutritious, and unfermentable, such as hay from grass that has run to seed and been threshed, the stems of grasses that have matured and withered in the pastures, fodder that has been thoroughly washed out by heavy rains, sedges, reedgrass, rushes, chaff, finely cut straw, and in the case of European sheep, the fibrous tops of heather contribute to this affection. Lack of water is one of the most potent factors, as an abundance of water to float the ingesta is an essential condition of rumination. Hence pasturage on dry hillsides, prairies or plains, apart from streams, wells or ponds is especially dangerous unless water is supplied artificially, and the winter season in our Northern states, when the sources of drinking water are frozen over, and when the chill of the liquid forbids its free consumption, is often hurtful.
Gerard attributes the affection to constant stabulation. This, however, has a beneficial as well as a deleterious side. It undermines the health and vigor, and through lack of tone favors gastric torpor and impaction, but it also secures ample leisure for rumination, which is so essential to the integrity of the rumen and favors the onward passage of its contents. With dry feeding and a restricted water supply it cannot be too much condemned, but with succulent food and abundance of water the alleged danger is reduced to the minimum.
Active work and over exertion of all kinds must be admitted as a factor. At slow work the ox can still ruminate, but in rapid work or under heavy draft this is impossible, and the contained liquids may pass over from rumen to manifolds conducing to impaction of the former, or fermentations may take place, swelling up the mass of ingesta and distending the walls of the first stomach. Similarly, cattle and sheep that are hurried off on a rapid march with full stomachs are greatly exposed to both tympany and impaction.
In speaking of dry, fibrous food and lack of water as factors, we must avoid the error of supposing that succulent or aqueous food is a sure preventive. In a catarrhal condition of the rumen or in a state of debility, impaction may readily occur from the excessive ingestion of luscious grass, wheat bran, potatoes, apples, turnips, beets, or cabbage.
Finally defects in the anterior part of the alimentary tract may tend to impaction. Salivary fistula or calculus cutting off the normal supply of liquid necessary for rumination, tends to retention and engorgement. Diseased teeth and jaws interfering with both the primary and secondary mastication has the same vicious tendency. Old cows, oxen and sheep in which the molar teeth are largely worn out, suffer in the same way, especially when put up to fatten or otherwise heavily fed. In this case there is the gastric debility of old age as an additional inimical feature.
Symptoms. These vary with the quantity and kind of ingesta also to some extent with the previous condition of the rumen, sound or diseased. They usually set in more slowly than in tympany. On the whole the disease appears to be more common in the stable than at pasture. The animal neither feeds nor ruminates, stands back from the manger, becomes dull, with anxious expression of the face, arching of the back and occasional moaning especially if made to move. The abdomen is distended but especially on the left side, which however hangs more downward and outward and tends less to rise above the level of the hip bone than in tympany. If it does rise above the ilium this is due to gas and it is then elastic, resilient and resonant on percussion at that point. The great mass, and usually the whole of the paunch is nonresonant when percussed, retains the imprint of the fingers when pressed, and gives the sensation of a mass of dough. The hand applied on the region of the paunch fails to detect the indication of movements which characterize the healthy organ. The ear applied misses the normal friction sound, but detects a crepitant sound due to the evolution of bubbles of gas from the fermenting mass. This is especially loud if the impaction is one of green food or potatoes, even though the gas remains as bubbles throughout the entire fermenting mass, instead of separating to form a gaseous area beneath the lumbar transverse processes.
The respiration is hurried, labored and accompanied with a moan, the visible mucosæ are congested, the eyes are protruded and glassy from dilatation of the pupils, the feet are propped outward, and the head extended on the neck. There may be signs of dull colicy pains, movements of the tail and shifting of the hind feet, in some cases the patient may even lie down but never remains long recumbent. There may be occasional passages of semi-liquid manure, though usually the bowels are torpid and neither passages nor rumbling sounds on the right side can be detected. When moved the animal usually grunts or moans at each step, and especially when going down hill, owing to the concussion of the stomach on the diaphragm. In cases due to green food the irritation may extend to the fourth stomach and intestines and a crapulous diarrhœa may ensue. The temperature remains normal as a rule. The disease is more protracted than tympany, yet after several hours of suffering and continual aggravation the dullness may merge into stupor, the mucosæ become cyanotic and death ensues from shock, asphyxia, or apoplexy.
Course. Termination. Many cases recover in connection with a restoration of the contractions of the rumen, the eructation of gas, in some rare cases vomiting or spasmodic rejection of quantities of the ingesta, and the passage of gas by the bowels. This may be associated with a watery diarrhœa, and loud rumbling of the right side, which may continue for twenty-four hours or longer. With the subsidence of the diarrhœa there comes a return of health, or there may remain slight fever, inappetence, suspended or impaired rumination, dullness, listlessness, and a mucous film on the fæces. This indicates some remaining gastro-enteritis.