A boil or abscess is a localized accumulation of infectious tissue and fluid in response to a bacterial infection. The most common infection in sheep is caseous lymphadenitis (CL), which localizes in the lymph nodes.
A variety of bacteria may cause an abscess, but the cause (CL) is corynebacterium pseudotuberculosis. It often causes multiple abscesses in the lymph nodes around the head, neck and shoulders. It may also affect internal organs, such as the liver, kidneys and lungs. It may result in chronic weight loss or death in extreme cases. Caseous lymphadenitis can spread between animals. When an external boil ruptures, the bacteria are dispersed. This can be a particular concern at shearing time. It may take several months for lesions to develop in newly infected animals. Individual abscesses can be lanced and drained or surgically removed. When Lancing or removing a lesion, you must exercise great caution to not further spread organisms to other sheep. There may still be internal abscesses that cannot be seen or removed. Antibiotics are generally of little benefit as they struggle to penetrate the thick capsule of tissue that forms around the infected area.
Maintain fences, feeders and corrals to minimize injuries. Shear the youngest sheep first and take great care to not rupture any abscesses. A vaccine is available but it must be administered when lambs are very young to promote immunity prior to exposure.
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