Longitudinal study of respiratory health in dairy farmers: influence of artificial barn fodder drying.

Factors influencing respiratory consequences of dairy farming have not been extensively investigated to date. To evaluate the effects of barn fodder drying on respiratory symptoms and lung function, a 5 yr follow-up study was performed in the Doubs (France). A cohort of male dairy farmers was analysed in 1990. The initial cross-sectional results suggested that barn-drying fodder may protect dairy farmers from lung function impairment. In 1995, 113 barn-drying farmers (92%) and 231 traditional-drying farmers (84%) were re-analysed. Barn and traditional fodder-drying farmers were compared for prevalence of symptoms and spirometric measures of lung function. After controlling for age, smoking status, altitude and cumulative exposure, barn-drying farmers compared to traditional-drying farmers had a lower prevalence of chronic bronchitis (4 versus 10%; p<0.05) and slightly higher values of forced expiratory volume in one second (FEV1) (p=0.06) and FEV1/vital capacity (VC) (p<0.01). Nevertheless, decline of the respiratory function parameters was not significantly different between the two groups. Variables positively and significantly associated to longitudinal decline of lung function parameters were: age (FEV1, FEV1/VC); altitude (VC, FEV1) and chronic bronchitis and dyspnoea at the initial survey (FEV1/VC). Persistence and emergence of chronic bronchitis, dyspnoea and symptoms at exposure were also significantly associated to an acceleration in the annual decline of the respiratory function. In conclusion, the mode of fodder drying does not seem to significantly influence the decline in lung function. Nevertheless, this study confirms the results of the initial cross-sectional analysis and supports the hypothesis that barn drying fodder may have a protective effect on respiratory health in dairy farming.