Equine grass sickness in Scotland: A case-control study of environmental geochemical risk factors.

The researchers studied whether the occurrence of equine grass sickness, a disease affecting horses in Scotland, has a relationship with the distribution of certain chemical elements in the environment. They found certain clusters of elements associated with such cases, but the correlation is complex and needs more investigation.

Objective of the Study and Hypothesis

• The study was intended to understand whether the geographical distribution of equine grass sickness (EGS) cases in eastern Scotland is linked to particular environmental chemical elements.
• The hypothesis was that the distribution of EGS might be due to inadequate levels of soil macro-and trace elements in the fields.
• If verified, changing the levels of certain elements could help to minimize the risk of EGS.

Methodology

• The researchers carried out a retrospective time-matched case-control study.
• Data for 455 geo-referenced EGS cases and 910 time-matched controls in eastern Scotland were used.
• They also utilized geological data from the British Geological Survey Geochemical Baseline Survey of the Environment stream sediment (G-BASE) and the James Hutton Institute, National Soil Inventory of Scotland (NSIS) datasets.

Results

• The statistical analyses identified three main clusters of elements associated with cases from the G-BASE dataset – higher environmental titanium and lower zinc; and from the NSIS dataset – higher environmental titanium and lower chromium.
• Additionally, the analyses noted lower aluminium, cadmium, copper, nickel, and lead, and higher calcium, potassium, molybdenum, sodium, and selenium environmental concentrations being linked to a case.
• However, the results were complicated due to a high degree of correlation between the chemical elements.

Conclusions and Suggestions for Further Work

• The researchers concluded that the findings seem to reflect soil-level risk factors for EGS rather than horse-level risk factors.
• However, given the complex correlations between elements, further work is required to confirm causality.
• If these associations were confirmed, interventions could be developed to alter concentrations of particular elements in the soil or grazing horses, with the aim of reducing the risk of EGS.
• The study also suggests an investigation into how these chemical elements could affect the growth of soil microorganisms implicated in the onset of EGS.