Abstract

Background: Exposure to animals, their feeds, and by-products contribute to respiratory symptoms among farmers.

Aims: To investigate the role of animal exposures and wheeze, and to assess whether their impact differs among susceptible subgroups, including atopics, asthmatics, and smokers.

Methods: Using the Agricultural Health Study, a cohort of pesticide applicators in Iowa and North Carolina enrolled in 1994–97, wheeze associated with animal production was evaluated and interactions among susceptible subgroups assessed. Logistic regression models were used to examine risk factors for wheeze in the past year among 20 468 farmers.

Results: Individuals raising animals requiring direct contact had the highest odds ratios (OR) for wheeze (OR_dairy = 1.26; OR_eggs = 1.70). A significant dose response was observed for both the number of poultry and the number of livestock on the farm. Farmers who performed veterinary procedures on a daily basis had an OR of 1.51. The odds of wheeze associated with poultry production was greater among atopic than non-atopic individuals. Milking cows daily increased the odds of wheeze in all individuals, with the largest association observed among atopic asthmatic individuals. The impact of dairy, poultry, and egg production varied among smoking groups. Past smokers had the highest odds ratios, followed by never smokers, and then current smokers. The OR_eggs was 2.88 among past smokers but only 1.46 for never smokers. The OR_eggs for current smokers of 0.80 might reflect self selection of exposure among smokers.

Conclusions: Results are consistent with animal production and respiratory symptoms, and suggest that subgroups may respond differently to exposure.