Occupational respiratory health of New Zealand horse trainers

Objectives: To confirm that working with horses is an occupational respiratory hazard and observed associations are not attributable to confounding. Methods: A postal survey of the respiratory health of 659 horse trainers and a comparison group of 506 vegetable growers was conducted. Data were analysed using logistic regression. Results: Relative to vegetable growers, horse trainers reported higher rates of chronic bronchitis [odds ratio (OR) = 6.8, 95% confidence interval (CI): 2.2-21.4] and organic dust toxic syndrome/farmers' lung (ODTS/FL) (OR = 3.5, 95% CI: 1.8-6.8). Grinding oats, spreading hay, and using powdered feed supplements were associated with increased respiratory symptoms among trainers. Associations between symptoms and working with horses increased for full-time workers. Conclusions: This study found evidence that working with horses is a risk factor for ODTS/FL and bronchitis. The associations did not appear to be explained by bias, including confounding. However, the possibility of confounding cannot be entirely ruled out, and confirmatory studies are needed. Future studies should consider inorganic dust exposures.