Abomasal Dilation and Emptying Defect of Suffolk Sheep
David Francoz
Definition and Epidemiology
Failure of abomasal transport and abomasal dilation has been described in adult sheep.1 The disease has been reported mainly in Suffolk breed and has occurred mostly in winter months in association with lambing and feeding of concentrates.
A similar syndrome has been described in two Hampshire,2 one Dorset,3 and one Texel sheep.4 An abomasal emptying defect syndrome has also been reported in Toggenburg goats, which could suggest that this syndrome may therefore occur in goats.5Animals described in reports from several teaching hospitals were adults of both sexes.1,6 Most cases are sporadic, but at least two outbreaks have been reported.1,6 The incidence in one report was 13 of 92 mature ewes affected in the flock during one winter.6 In the other report, 5 ewes of a flock of 200 ewes were submitted for necropsy in the same day.1 In both studies, pedigree analysis of affected sheep showed no hereditary pattern. One report from a diagnostic laboratory in England described abomasal impaction in a Texel ewe and in a Suffolk ram that were simultaneously diagnosed as having scrapie.4 It remains to be seen whether any causative connection exists between the two diseases. In one study, six sheep were immunohisto chemically tested for scrapie; five results were negative and one was positive, and the affected sheep had equivocal microscopic lesions.1
Pathophysiology
The mechanisms underlying the dilation of the abomasum and the failure to transport ingesta to the intestines are unknown. None of the problems commonly associated with abomasal impaction and dilation in cattle have been identified in affected Suffolk sheep. It has been advanced that abomasal emptying defect of Suffolk sheep may be an acquired form of dysautonomia.1
Clinical Signs and Differential Diagnosis
The disease is manifested primarily by anorexia and weight loss.
Most patients eventually die. The following clinical signs have been reported in affected animals but are not always present: watery green diarrhea; ruminal tympany; pear-shaped abdominal distention; increase or decrease in or absence of ruminal contractions; a palpable (by ballottement) firm mass in the right lower abdomen; mild abdominal pain; tachycardia; duration of observed signs from days to months; partial to total anorexia; dullness and depression; marked to undetectable weight loss; and ketonuria.This syndrome should be differentiated from other wasting diseases of sheep such as malnutrition, parasitism, dental problems, Johne's disease, caseous lymphadenitis, other chronic infections, and neoplasia. Abomasal emptying defect is distinguishable by the palpable abomasum in advanced cases and the exclusion of other possible problems. Other causes of abomasal enlargement or impaction resembling those reported in cattle must also be considered. However, when a mature Suffolk sheep from a well-nourished flock shows weight loss and a palpable abomasum, this syndrome must be considered highly likely. Confirmation may require necropsy or exploratory surgery.
Ancillary Tests
Reports on cases diagnosed in North America have found CBC and systolic blood pressure to be of little benefit in the diagnosis.6 The hypochloremic metabolic alkalosis common in cattle with abomasal problems may be present2,7 but is not consistently observed in affected sheep.3,6,8,9 Increased liver enzyme levels are frequently reported in affected sheep and goats and were associated with hepatic congestion and ischemia secondary to abomasal distention.3,5,6,7 Mild hypocalcemia was observed in all cases in one report.5 Because of internal vomiting, elevated ruminal chloride ion values (34 to 130 mEq/L; normal, 8 to 15 mEq/L) are also frequently reported in published reports.2,3,6,7,9
Treatment and Prognosis
Medical therapy alone with cathartics and laxatives has been of limited benefit. Mineral oil, dioctyl sodium sulfosuccinate, and magnesium sulfate have all been used.
Neostigmine and calcium gluconate were not useful.8 Abomasotomy has led to death from complications in many affected sheep,6,8 but those that survived more than 2 days manifested recrudescence of clinical signs within 12 weeks.8 Ewes treated with metoclopramide (dosage not reported) have shown varying degrees of recovery; some of them survived for 12 weeks but continued losing weight.6 Experimental studies in cattle and sheep have failed to demonstrate any beneficial effect of metoclopramide on abomasal emptying.10,11 On the other hand, erythromycin has been shown to increase abomasal emptying rate in lambs.12 However, in a context of judicious use of antimicrobial drugs, the administration of erythromycin for its prokinetic properties is questionable and is not recommended. Despite these successes, most affected sheep die of cachexia. Because of the expense, poor response, and risks associated with abomasotomy, this treatment is reserved for valuable breeding stock.Necropsy Findings
The abomasum is greatly distended in sheep that die of this condition. The contents are either dry or liquid but most often have resembled normal ventral ruminal sac contents. Investigators always reported a patent pylorus. Normal ingesta have been observed throughout the remainder of the intestinal tract. Incidental findings have included aspiration of ruminal contents and subsequent pneumonia, abomasal ulcer with local peritonitis, passive congestion of the liver, megaesophagus, and esophageal ulcers. Reports of histopathologic findings include no lesions other than thinning of the abomasal muscle layers (presumably as a result of stretching),6 mononuclear cell infiltration of the main muscle layers of the abomasum,8 and, in one case, myxomatous changes in the abomasal branches of the vagus nerve.9 Chromatolytic and necrotic neurons without signs of inflammation within the celiacomesenteric ganglia were found in all six affected sheep examined in one study.1
Prevention and Control
Until more is known about the pathogenesis of this specific defect in abomasal function in Suffolk sheep, no useful recommendations for prevention can be made.