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United Suffolk Sheep Association |
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Abomasal Emptying Defect Michelle Kopcha, DVM, MS Large
Animal Clinical Sciences/Veterinary Teaching Hospital Many producers are all too familiar with common diseases that can adversely affect the health of their sheep such as caseous lymphadenitis, chronic pneumonia, internal parasites and Johnes. A syndrome that is not so common and not so readily recognized is abomasal emptying defect (AED). The following series of questions and answers may help owners better understand this syndrome: WHAT IS ABOMASAL EMPTYING DEFECT (AED)? This condition affects sheep that are usually 2 years of age or older. For reasons that are as yet unknown, the abomasum of an animal with AED does not empty normally. There is no mechanical obstruction to the outflow tract of the abomasums of sheep that have AED, and this failure to empty leads to gradual enlargement of the abomasum, and loss of appetite and weight. WHAT BREED(S) OF SHEEP ARE AFFECTED WITH AED? Suffolk is the predominant breed affected. This condition has also been reported in Hampshire, Dorset and Texel breeds, and affects both males and females. WHAT CLINICAL SIGNS ARE OBSERVED WITH AED? Sheep affected with AED do tend to display some very characteristic clinical signs. The condition more commonly affects individual animals, rather than occurring as a flock problem. Oftentimes, owners report that the affected individual has continued to loose weight despite multiple dewormings, and providing additional nutrition and individual attention. Also, the animal will appear “bloated” on either or both sides of the abdomen, despite the fact that it has been off-feed. Usually animals that are off-feed develop a sunken appearance on both sides of the abdomen. Typically, there is no fever. The animals do produce fecal material, but usually the amount is less than normal. The feces may be firm and pelleted, or soft and not well pelletted. These animals are usually partially or completely off-feed. WHAT CAN BE DONE TO DIAGNOSE AED? History and clinical signs as described above are the tip-offs to suspecting that an animal may have AED. There are no characteristic changes seen in complete blood counts (CBC) or serum chemistry profiles, although running these tests may help to identify other problems that an animal may have. Abdominal imaging using radiography or ultrasonography may be useful, but may be difficult to interpret. In this author’s opinion, the best live animal test is evaluation of a rumen sample for its chloride content. A rumen fluid sample may be obtained by placing a stomach tube into the rumen and attempting to aspirate fluid. Another method involves inserting a needle through the skin and into the rumen from the left side of the abdomen to aspirate rumen contents. The sample is submitted to a clinical pathology laboratory for assessment of its chloride concentration. Normally, the rumen chloride content is less than 15 mEq/L. In cases of AED, this level is at least 2 times the normal level because the chloride from the abomasum backs up into the rumen. Definitive diagnosis of AED is made by observing the enlarged abomasum without an associated obstruction of the outflow tract, either during an abdominal exploratory surgery or necropsy examination. WHAT TREATMENT IS AVAILBLE FOR AED AND WHAT IS THE PROGNOSIS? Unfortunately, there is not a good long-term prognosis associated with this condition. If the diagnosis is made early, before the abomasum has enlarged too much, the animal may respond to intensive therapy. This usually includes abdominal surgery to empty the abomasum, intravenous fluid therapy, and use of a specific drug that stimulates abomasal motility (metoclopramide). With this treatment, it may be possible to “buy some time” for the animal. For example, a pregnant ewe may be able to survive through her gestation, or a ram may be able to continue to breed through a breeding season. However, although the cause of this condition is unknown, it may be genetically linked. Given this concern, it may not be wise to pursue treatment or to breed affected animals or their offspring. HOW CAN AED BE PREVENTED? Since the underlying cause of AED is unknown, there are no recommendations for prevention other than what was suggested above regarding breeding. In summary, it is important to remember that there are numerous reasons for weight loss to occur in sheep. Determining the underlying cause(s) requires a good understanding of diseases, the ability to work through the possibilities using powers of observation, knowledge of the flock and its management, and appropriate use and correct interpretation of diagnostic tests (blood/fluid sampling, fecal examination, diagnostic imaging and necropsy). The hallmark signs of AED include 1) it affects adult sheep, 2) weight loss with decreased appetite and fecal output occur, 3) distention of the abdomen on either one or both sides will be observed, and 4) a useful diagnostic test is evaluation of the chloride level in a rumen fluid sample. Although some animals may respond to treatment, the long-term prognosis is poor. Until there is more information regarding the cause of AED, it may be a good management decision to cull AED animals from the breeding flock.
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