Six year longitudinal study of respiratory function in dairy farmers in the Doubs province

A previous study, carried out in 1986 in France, showed the prevalence of respiratory symptoms and of respiratory function impairment to be higher in dairy farmers than in a control group of nonexposed subjects living in a rural zone. In order to confirm the harmful effect of dairy farming, the two groups were re-studied 6 yrs later at the same period of the year. One hundred and ninety-four (77.6%) farmers and 155 (62%) control subjects were available for re-examination. Non-re-evaluated subjects were comparable to reevaluated subjects for age, sex, smoking and respiratory symptoms and function at initial evaluation. Dairy farmers consistently had more respiratory symptoms and lower levels of respiratory function than did control subjects. In the study populations as a whole, the mean annual decline in vital capacity (VC) and forced expiratory volume in one second (FEV1) was slightly, but nonsignificantly, higher in farmers than in control subjects: in mL(.)yr(-1) (sD), -43.1 (68.2) versus -37.9 (60.2) for VC and -32.8 (56.7) versus -30 (47.2) for FEV1. There was a positive interaction between farming and age (i.e. duration of exposure in this cohort) on respiratory function decline, and in male subjects aged greater than or equal to 45 yrs, dairy farming was associated with an accelerated loss in VC (p<0.05) and FEV1 (p<0.05) after controlling for age, smoking, height and geographic location in a multiple linear regression model. Initial values of respiratory function, age and pack-years smoked (only for VC) were the other variables found to be significant determinants of decline in lung function. In conclusion, this study mainly suggests that dairy farming is associated to a very moderate accelerated loss in respiratory function that increases with duration of exposure and is significant in older male subjects.