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The stomachs of ruminants are closely associated anatomically and functionally, and disease of one usually affect the others. Bacterial digestion and fermentation, and physical maceration by contraction of the stomach walls are the two main functions of the forestomachs and the two are interdependent. Thus abnormality of one leads to abnormality of the other and of the two the motility is most readily examinable. Ruminal motility is therefore used as an index of digestive function in the ruminant.
Both afferent and efferent fibers are carried in the vagus nerves and damage to one or other branches of the nerve causes interference with normal movements and produces the syndrome of vagus lndlgestion.
Much mixing of the contents of the rumen and reticulum takes place during ruminal movements which occur at the rate of 1 to 3 per minute, the more rapid rate occurring soon after feeding.
During each reticular contraction fluid and food particles, particularly heavy grain, pass into the reticulo-omasal orifice and into the omasum and abomasum. It is this passage of heavy grain directly into the abomasum, without in many instances proper digestion in the rumen, which may lead to over loading of the abomasum and resultant displacement or torsion of this organ. It may also be important in the pathogenesis of enterotoxemia caused by Clostridium perfringens Type D.
Simple indigestion is caused by atony of the forestomachs and is characterized clinically by anorexia lack of ruminal movement and constipation.
The disease is common in dairy cattle because of the variability in quality and the large amounts of the food consumed. It is not commonly observed in beef cattle or sheep probably because they are less heavily fed. The common causes are dietary abnormalities of minor degree including indigestible roughage, particularly when the protein intake is low, mouldy, over-heated and frosted feeds, and moderate excesses of grain and concentrate intake. Gross overfeeding usually occurs when cattle or sheep gain accidental access to large quantities of grain or are suddenly introduced to high grain diets in feed-lots. Indigestion is more common when heavily fed cows are fed a little more concentrate than they can digest properly. Sudden change to a new source of grain, especially from oats to wheat or barley may have the same effect. Indigestible roughage may include straw, bedding or scrub fed during drought periods. Depraved appetite may also contribute to the ingestion of coarse indigestible material. Although good quality ensilage cannot be considered an indigestible roughage, cases of indigestion can occur in cattle which are allowed unlimited access to it. It is not uncommon for Holstein cows to eat 90 to 100 lb. of ensilage daily in such circumstances and the high intake of acetate and acetic acid may be sufficient to depress their appetite. Prolonged or heavy oral dosing with sulphonamides or antibiotics may cause indigestion due to inhibition of the normal ruminal flora.
Changes in the pH of its contents markedly affect the motility of the rumen and in cases caused by overeating on grain an increase in acidity is probably of importance. High protein diets including the feeding of excessively large quantities of legumes or urea, also depress motility because of the sharp increase in alkalinity which results. The simple accumulation of indigestible food may physically impede ruminal activity. Putrefaction of protein may also play a part in the production of atony. The toxic amides and amines produced may include histamine which is known to cause ruminal atony when given intravenously and to be reversed by the administration of anti-histamine drugs.
Affected cattle usually show a pronounced fall in milk yield caused probably by the sharp fall in volatile fatty acid production in the atonic rumen.
A reduction in appetite is the first sign and is followed closely in milking cows by a slight drop in milk production. Both occur suddenly, the anorexia may be partial or complete but the fall in milk yield is relatively slight. The animal's posture is unaffected but there is mild depression and dullness. Rumination ceases and there is constipation with scanty, firm feces in most cases although diarrhea may occur on damaged feeds. Ruminal movements are depressed in frequency and force or are absent. There may be moderate tympany, especially with frozen and damaged feeds or in allergy but the usual finding is a firm, doughy, rumen without obvious distension.
There is no systemic reaction and the pulse, temperature and respiration rates are unaffected. Pain cannot be elicited by percussion of the abdominal wall. Most cases recover spontaneously or with simple treatments in about 48 hours.
Examination of the urine for ketone bodies is usually necessary to differentiate indigestion from acetonaemia.
The major problem is to differentiate indigestion from acetonaemia and traumatic reticuloperitonitis. Acetonaemia occurs during the first two months after calving and is characterized by marked ketonuria. Traumatic reticuloperitonitis is manifested by a sharper fall in milk yield, a mild elevation of temperature and pain on percussion of the ventral abdomen. Vagus indigestion is not usually accompanied by fever but runs a protracted course and may be accompanied by abdominal distension and hypermotility or hypomotility of the rumen. Abomasal displacement usually occurs immediately after parturition, is accompanied by ketonuria and abomasal sounds in the lower left flank, and runs a protracted course, often for months. The initial states of some cases of abomasal torsion may be difficult to distinguish clinically from indigestion but they always terminate fatally. Acute ruminal impaction is a much more serious disease and is accompanied by signs of dehydration and nervous derangement. A history of engorgement on grain is usually forthcoming.
Secondary ruminal atony occurs in many diseases, especially when septicaemia or toxaemia are present but there are usually additional clinical signs to indicate their presence. Parturient paresis of cattle and allergic and anaphylactic states are usually accompanied by ruminal stasis but do not cause a syndrome of indigestion, motility returning to normal as soon as the cause is corrected.
Without knowledge of the aetiology, treatment is symptomatic, consisting primarily of the use of drugs.
Parasympathetic stimulants are widely used as Rumenatorics but have the disadvantage of creating undesirable side-effects and being very transitory in their action. Large doses depress rumen activity but small doses repeated at short intervals increase ruminal activity and promote violent emptying of the colon. Carbamylcholine chloride, physostigmine and neostigmine are most
commonly used. The last is the most effective and should be given at a dose rate of 2.5mg. per 100 lb. body weight.
Epsom salt (1 to 2 pounds) and other magnesium salts are reasonably effective and have the merit of simplicity and cheapness. Anthraquinone purgatives in doses of 8 to 15 9. are commonly used with apparent good results, and strychnine preparations (containing up to 65 mg. of strychnine as a single dose for an adult cow) enjoy a good reputation.
More rational therapy should include the use of alkalis, such as magnesium hydroxide or carbonate when the rumen contents are excessively acid, or of an acid, such as acetic acid or vinegar, when the reaction is alkaline. A sample of rumen fluid can be readily obtained and the Ph determined approximately by the use of reagent paper. If there is inspissation of ruminal contents 3 to 4 gallons of normal saline should be administered by stomach tube.
Case of indigestion which have run a course of more than a few days, and animals suffering from prolonged anorexia due to any cause suffer an appreciable loss of ruminal microflora, especially if there have been marked changes in pH. Reconstitution of the flora by the use of rumen transplants is highly effective. An abattoir is the best source of material but it can be obtained from living animals by reaching into the mouth or kneeing the animal in the ribs as a bolus is regurgitated. The transplant material should be mixed with water, strained and administered as a drench or by stomach tube. Repeated dosing is advisable. The infusion will keep for several days at room temperature.
When affected animals resume eating they are best tempted by good, stalky meadow or cereal hay. Good quality alfalfa or clover hay, green feed and concentrate may be added to the diet as the appetite improves.
