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

This research article studied the epidemiological and pathological characteristics of late-term horse abortions in central Kentucky associated with mare reproductive loss syndrome (MRLS). The results showed that many cases occurred simultaneously, suggesting an environmental trigger, and presented common microscopic lung abnormalities, but no single cause could be identified.

Methods and Data Collection

• The data for this study was collected by reviewing records from the University of Kentucky Livestock Diseases Diagnostic Center. The records examined focused on 433 late-term abortions associated with MRLS in horses.
• Details about the timing and occurrence of these abortions were analyzed to understand the distribution of the cases.

Epidemiological Findings

• The study found that the abortions were clustered around a specific, brief period of time. This is a significant finding as it suggests that the causes were related to a shared environmental exposure.

Pathological Findings

• The most commonly observed abnormalities from the study were specific microscopic lung lesions — specifically, squamous epithelial cells present in the lung’s oxygen-exchange sections (alveoli), often accompanied by the presence of inflammatory cells in the same area.
• Pathogens like non-beta-hemolytic Streptococcus and Actinobacillus were commonly found, seen in 52% and 19% of fetuses respectively. Approximately 44% of the fetuses showed signs of inflammation of the placenta or umbilical cord (placentitis or funisitis).

Overall Conclusions

• Despite the patterns observed in timing and the presence of common lung abnormalities, the researchers did not identify a single, conclusive pathological indicator for MRLS-associated abortion.
• This report thus provides key insights into the characteristics of MRLS-associated abortions, but conclusive determinations about the cause of MRLS could not be made based solely on the findings of necropsy examinations (animal autopsies).