Equine grass sickness in Scotland: A case-control study of environmental geochemical risk factors.
Authors: Wylie C E, Shaw D J, Fordyce F M, Lilly A, Pirie R S, McGorum B C
Journal: Equine veterinary journal
Summary
# Editorial Summary: Equine Grass Sickness and Soil Geochemistry in Scotland Equine grass sickness (EGS) shows a marked geographical distribution that cannot be fully explained by known risk factors, prompting investigation into whether soil elemental composition might play a protective or predisposing role. Wylie and colleagues conducted a retrospective case-control analysis of 455 confirmed EGS cases matched against 910 controls across eastern Scotland, overlaying case locations against two major geochemical datasets: stream sediment analysis (G-BASE) and soil inventory data (NSIS). Multivariable statistical modelling identified consistent patterns associating EGS occurrence with elevated environmental titanium alongside deficient zinc (G-BASE) and chromium (NSIS), whilst univariable analyses suggested protective associations with aluminium, cadmium, copper, nickel and lead—though the interpretation is complicated by substantial inter-elemental correlation. The findings point towards soil-level rather than systemic nutritional factors influencing EGS risk, yet the authors appropriately emphasise that demonstrating association is not equivalent to establishing causation, and that the mechanistic relationship between soil chemistry, soil microbial communities (implicated in EGS aetiology), and disease pathogenesis remains unclear. For practitioners, this work suggests that geographical EGS risk may be modifiable through environmental intervention, but further research into element bioavailability, microbial ecology, and potential supplementation strategies is essential before clinical recommendations can be made.
Read the full abstract on PubMed
Practical Takeaways
- •EGS risk may be influenced by soil geochemical composition in specific geographical areas; farmers should be aware that field management practices cannot fully mitigate location-dependent elemental deficiencies
- •Further research is needed before recommending soil supplementation or dietary interventions targeting specific elements—current evidence is associative rather than causal
- •Practitioners should consider soil geochemical profiling as part of EGS risk assessment in affected regions, particularly eastern Scotland
Key Findings
- •Higher environmental titanium and lower zinc levels were associated with EGS cases in G-BASE geochemical dataset
- •Higher environmental titanium and lower chromium levels were associated with EGS cases in NSIS soil dataset
- •Study identified soil-level rather than horse-level risk factors, but correlations between elements complicate causality interpretation
- •Environmental concentrations of aluminum, cadmium, copper, nickel and lead were lower in EGS case locations compared to controls