Functional and histopathological evidence of cardiac parasympathetic dysautonomia in equine grass sickness.

The researchers examined horses suffering from a disease called grass sickness to check for abnormalities in the heart’s parasympathetic terminal ganglia, a part of the nervous system related to heart function. They found noticeable differences between the hearts of ill horses and healthy ones, indicating a connection between the sickness and certain heart conditions.

Research Methodology

• They took samples from three normal horses and five horses affected by the grass sickness to evaluate their cardiac ganglia. This part of the heart is controlled by the parasympathetic nervous system, which maintains the body’s resting state.
• To ascertain functional abnormalities, they applied a method called time domain analysis (TDA) to evaluate heart rate variability in eight horses with grass sickness. This technique measures the variations in time intervals between heartbeats and can indicate potential cardiac diseases.
• Moreover, they also performed a comparative analysis between the affected horses and 16 healthy horses – matched according to breed, sex, and age – to strengthen the validity of their findings.

Findings

• There were significant histopathological changes visible in the cardiac ganglia of horses affected by grass sickness. These alterations were similar to those observed in other ganglia of horses with the disease.
• Furthermore, the results from TDA revealed crucial differences in heart function between the normal and diseased horses.
• For instance, two specific indicators – triangular index and the sNN100 index – obtained from TDA show significant discrepancies between the two groups. These indices are used to represent the overall variability and the short-term components of heart rate variability respectively.
• The greatest difference was found in the R-R interval, a measure of time between two peak points in the heart’s electrical cycle. This measure was significantly greater in sick horses, showing a clear anomaly in their heart function.

Conclusion

• The study concluded that horses with grass sickness exhibited both functional and pathological abnormalities in their heart’s parasympathetic control system. This signals a decentralization in the control of heart functions in these horses, potentially making them less responsive to body commands.

This research provides important insights into the pathological effects of grass sickness in horses and may potentially open avenues for further exploration into effective treatment and disease management protocols.