Metabolic Diseases

Bloat

Ruminal tympany, or bloat, is less common in goats than in cattle and sheep. When it occurs, however, it must be con­sidered a medical emergency, as in other ruminant species.

Etiology and Pathogenesis

Gas production is a normal outcome of rumen fermentive activity. Ordinarily, gas rises to the dorsal sac of the rumen and is discharged by the orderly process of rumination and eructation. Frothy bloat derives from nutritional causes. Under certain dietary conditions, such as the feeding of legumes or finely ground grains, gas bubbling through the rumen content can no longer freely coalesce in the dorsal sac, but rather is trapped in a stable foam in the liquid phase of the rumen content. Stable foam cannot be freely eructated, and a progressive distension of the rumen ensues as additional gas becomes trapped. This progressive ruminal distension can be fatal as a result of subsequent

respiratory and cardiovascular compromise. Experimentally in goats it has been documented that ruminal insufflation leads to decreased cardiac output, increased blood pres­sure, and increased total peripheral resistance due to obstruction of venous return by the distended rumen (Reschly and Dale 1970).

Free gas or secondary bloat occurs when gas accumulat­ing normally in the dorsal sac of the rumen cannot be expelled because of extraruminal obstructions to outflow. When free gas cannot be eructated, progressive ruminal distension ensues, with consequences similar to those just described.

Epidemiology

Bloat occurs in goats throughout the world. All goats with a mature functional rumen are at risk. Factors that have been identified as predisposing goats to frothy bloat include unaccustomed ingestion of lush legumes such as clover or alfalfa, either as green feeds or as new hay, recent turnout to legume pastures, and even turnout to grass pastures if they are wet.

Free gas bloat occurs only sporadically in goats, usually secondary to esophageal choke. Pieces of apple or carrot are common foreign bodies. A cud can lodge in the esopha­gus, particularly in debilitated or sick animals and in ani­mals with inadequate water supply. Thymomas or internal abscesses in the anterior abdomen or mediastinum associ­ated with caseous lymphadenitis or other causes can also produce secondary or free gas bloat by compression of the cardia or esophagus.

Clinical Signs

Frothy bloat can occur within hours of exposure to the offending feed or feeding situation. Many cases of bloat are first recognized by finding animals dead at pasture. In the initial stages of the disease, affected animals become anx­ious and uncomfortable and stop eating. The most charac­teristic sign is a progressive distension of the abdomen, particularly apparent on the left side and high in the left paralumbar fossa. Percussion of this area reveals the tight, tympanic feel of the distended rumen and a drum-like sound. As the distension progresses, animals become more uncomfortable, stamping their feet, vocalizing, salivating, urinating frequently, and moving with a stilted gait. Without intervention, these animals become recumbent, exhibit marked labored respiration, and die within one hour.

In free gas bloat, signs are similar. Salivation is more pro­nounced if the esophageal obstruction is high and com­plete and saliva cannot be passed to the rumen. If intraluminal obstruction is not complete, or if the pressure of accumulating gas in the rumen can override an extralu­minal obstruction, gas is intermittently expelled and the abdominal distension caused by the rumen may be less pronounced, with less severe tympany.

Clinical Pathology and Necropsy

Because of the acute nature of bloat, laboratory investiga­tions are not performed. Necropsy is commonly employed in the diagnosis of bloat because the condition often pro­ceeds to the fatal stage without detection. In a fresh nec­ropsy of a case of frothy bloat, the ruminal distension is obvious and large amounts of froth are present within the rumen. In free gas bloat, rumen distension is present, but the rumen does not contain froth. Careful inspection of the alimentary tract and surrounding structures from the mouth through the forestomachs should identify the source of secondary obstruction leading to free gas bloat. When animals are found several hours after death, diagno­sis becomes more problematic, particularly in warm weather. Rumen distension with gas caused by the contin­ued fermentive action of rumen flora after death eventu­ally produces bloat in all carcasses. Froth also breaks down after death, causing frothy bloat to appear as free gas bloat. Examination of the carcass may help to establish the pres­ence of antemortem bloat. In bloat cases, there is conges­tion of tissues in the anterior portions of the carcass and blanching or paleness of tissues in the caudal portions, reflecting peripheral vascular changes induced by the dis­tended rumen. A line of demarcation (“bloat line”) may be noted between red congested esophageal mucosa in the cervical region and pale mucosa in the thoracic esophagus.

Diagnosis

Bloat is easily confirmed by physical examination. It is important to determine whether the condition is primary or secondary, because this affects treatment and subsequent management decisions. The difficulty in the diagnosis of bloat comes when animals are found dead. Because bloat may be a normal postmortem change, it is necessary to rule out all possible causes of sudden death under the circum­stances in which the animal is found.

Treatment

Timely intervention is essential. Simple passage of a stom­ach tube, though often effective in relieving free gas bloat, does not correct frothy bloat unless the foam is first broken down. Cooking oils or mineral oil given orally in a dose range of 100-200 cc can be effective, but may not work as rapidly as some of the commercial anti-frothing agents available. If given as a drench, care must be taken to avoid aspiration pneumonia. Linseed oil should not be used, because it is associated with indigestion in goats. Oil of tur­pentine is a common home remedy. Though effective, it can taint meat and milk for five days after use.

There are a number of commercial, surface-acting (sur­factant) agents that are also effective in degrading foam and results may be seen within minutes. Poloxalene is available as a concentrate to be diluted for use as a drench. It is dosed at a rate of 100 mg of poloxalene per kg bw. Dioctyl sodium sulfosuccinate (DSS; 15-30 mL dose), polymerized methyl silicone (10-15 mL dose), and docu­sate sodium (1.4 g dose) are other effective compounds. When large numbers of animals are affected and treatment time becomes a critical factor, anti-frothing agents can be injected directly into the rumen through the distended left paralumbar fossa using an 18-gauge needle, rather than administering them orally by stomach tube. Polymerized methyl silicone works more effectively than poloxalene when given by this route. The newer, alcohol ethoxylate detergent products are more effective in controlling frothy bloat associated with grain ingestion than are poloxalene and the other products, which perform best with legume- induced bloat.

Forced exercise after administering oils or surfactants helps break down foam and promotes expulsion of gas. If animals are recumbent, rolling the goat or massaging the rumen may help distribute the oil and break down the foam.

Trocharization of the rumen through the left paralumbar fossa can be lifesaving in goats in the terminal stages of bloat. However, this invasive treatment should be reserved for the most advanced cases, due to the potential sequelae of peritonitis and prolonged rumen dysfunction. Goats tro- charized for relief of bloat should be placed on a 3-5-day course of broad-spectrum antibiotic therapy after the procedure.

Control

Because goats are generally not managed in feedlots, con­trol of feedlot bloat is not a major concern. When goats are fed grain, concentrate feeds should not be too finely ground and should not be abruptly introduced into the ration. For goats that show a tendency to bloat when fed grain, top dressing of the grain with vegetable oils can be helpful, as can the addition of poloxalene to mineral supplements or mineral blocks.

If grazing of legume pastures is an integral part of the goat management system, the risk of bloat can be high. A number of interventions have been described for cattle and/ or sheep to reduce that risk. They include daily drenching of individual animals with oils before turnout, including anti-frothing agents such as poloxalene in feed or mineral supplements, feeding the ionophores monensin or lasalocid or administering a sustained-release monensin capsule, and spraying oils or fats directly onto pasture. Managing the pasture itself can also be of value; interventions include sowing grasses with legumes, using forage types high in condensed tannins, strip grazing, and swathing and wilting alfalfa for 24 hours before turning animals out onto pasture. All these techniques and interventions are discussed in more detail elsewhere (Constable et al. 2017).

The most fundamental intervention for controlling pas­ture bloat in goats is to adapt them gradually to pastures in spring, turning them out initially for short periods on a full stomach of hay to limit pasture consumption.

Rumen Impaction

Rumen distension secondary to impaction has been caused in the goat by sand ingestion and by prolonged feeding of low-energy, high-fiber diets, such as horse feed containing more than 25% oats in conjunction with poor-quality grass hay (Guss 1977). It has also been associated with the feed­ing of bread, pollard, pellets, wheat, corn, or barley in excessive proportions of the total ration (King 1980c). In northern India, rumen impaction in goats and other rumi­nants is more common in the hot, dry summer season when green fodders are unavailable, water is scarce, and the diet is composed mainly of low-grade, dry roughages (Prasad and Rekib 1979). The distension is primarily on the left, in the ventral abdomen, and ballotment reveals a firm, doughy consistency to the rumen content.

In recent years, the global proliferation of plastic bags in commerce and their careless disposal in the environment have become an important cause of ruminal impaction in goats. This is particularly the case in developing countries, where flocks of goats may be brought to trash bins or gar­bage dumps to forage, or when drought drives goats to eat items in the environment not normally consumed. Reports of rumen impaction due to plastic bags in goats have come from Nigeria (Otesile and Akpokodje 1991; Remi- Adewunmi et al. 2004), Jordan (Hailat et al. 1998), the Sudan (Abdel-Mageed et al. 1991), and South Africa (Donkin and Boyazoglu 2004). There is some indication that goats develop pica for plastic bags and consume them preferentially (Abdel-Mageed et al. 1991). Other foreign materials reported in association with rumen impaction in goats include cloth, leather, twine, and rope.

In addition to developing a firm, distended rumen, ani­mals with rumen impaction become dull and listless, appe­tite is reduced, and milk production falls off. Cud chewing ceases, there may be mild bloating, and the feces may become scant, dry, and mucus covered. Progressive weight loss and debilitation ensue if the condition is not recog­nized and treated.

For sand impaction, one week of daily drenching with 60 g of magnesium sulfate is recommended. Each drench should be followed by manual kneading of the lower left abdomen to break up impaction. If impaction persists, rumenotomy may be required. Up to 9.1 kg of sand has been removed from a goat rumen (King 1980b). Animals should be fed in racks or troughs off the ground when pos­sible. For fibrous impactions, daily oral dosing with min­eral oil and DSS may soften impactions, but rumenotomy may be necessary. When fibrous impactions are diagnosed, the ration needs to be evaluated and corrected to provide more digestible energy and less fiber. Rumenotomy is required for the treatment of goats with rumen impaction due to plastic bags.