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Why are certain premises at increased risk of equine grass sickness? A matched case-control study.

REASONS FOR PERFORMING STUDY
Equine grass sickness (EGS) occurs repeatedly on certain premises over time. Few studies have sought, or identified, the determinants of this phenomenon in order to inform advice on disease prevention strategies.


HYPOTHESIS
Premises-level risk factors are important determinants of whether EGS occurs.


METHODS
A matched case-control study was undertaken. Sixty premises giving rise to one or more histologically confirmed case of EGS and 120 time-matched control premises were sampled. Data were collected on pasture management, soil nutrient content, pasture nutrient content and local weather conditions for 2 weeks prior to the onset of disease. Data were analysed by conditional logistic regression.


RESULTS
Multivariable modelling identified an association between EGS and increased soil nitrogen content, pasture disturbance and previous occurrence of EGS on the premises. None of the meteorological variables recorded in this study were significantly associated with EGS occurrence. No relationship between certain management practices (e.g. harrowing, fertilisation, reseeding) and the risk of EGS was detected.


CONCLUSIONS AND POTENTIAL RELEVANCE
This information is useful in understanding the causal pathway of EGS and may be used in the formulation of evidence-based disease avoidance strategies.