Descriptive epidemiology of late-term abortions associated with the mare reproductive loss syndrome in central Kentucky.

Epidemiological and pathological findings of 433 late-term abortions associated with the mare reproductive loss syndrome (MRLS) in central Kentucky were identified by reviewing the records of the University of Kentucky Livestock Diseases Diagnostic Center. The distribution of dates of abortion was clustered during a brief period of time, presumably from a simultaneous environmental exposure. The most common pathological findings were microscopic pulmonary lesions consisting of squamous epithelial cells present in alveoli with or without concurrent infiltration of inflammatory cells (neutrophils, macrophages, or monocytes) in the interstitium or within alveoli. Isolation of a non-beta-hemolytic Streptococcus (52% of fetuses) or an Actinobacillus sp. (19% of fetuses) was common. Placentitis or funisitis was identified in 44% of fetuses. No single pathological finding, however, was pathognomonic for MRLS-associated late-term abortion. This report describes the pathological findings characterizing the MRLS-associated abortion. A cause of MRLS could not be determined from necropsy findings.