Contact with livestock - a protective effect against allergies and asthma?

Background A 'protective farm factor' possibly related to livestock exposure is hypothesized to reduce the risk for allergic sensitization. Objective The purpose of this study was to determine whether 4-H club youth, who have opportunities for contact with livestock through club activities, have reduced risks of respiratory and allergic symptoms according to residence on a farm or exposure to livestock. Methods A cross-sectional postal survey was completed by British Columbia 4-H members 8-20 years of age; a subset underwent skin prick testing as well. The association of farm residence and livestock exposure variables with symptoms were evaluated using logistic regression with adjustment for age, sex, cat and/or dog ownership, parental history of allergic disease, parental education, number of older siblings and exposure to smokers at home. Results Questionnaires were completed by 1158 participants (response rate 50.3%); of these, a subset of 317 had skin prick tests (SPTs) (response rate 64.4%). Current residence on a farm was associated with a lower prevalence of ever having wheeze and asthma, as well as symptoms of atopic dermatitis. Variables relating to residence in a farm or rural area with livestock were more strongly associated with respiratory and allergic symptoms than were the livestock exposure variables such as frequency of contact and hours of barn use. The adjusted odds ratios for living in a farm residence in comparison with a rural non-livestock area were 0.49 (95% confidence interval (CI) 0.27-0.89) for diagnosed asthma, 0.51 (95% CI 0.30-0.85) for allergic rhinitis and 0.45 (95% CI 0.24-0.84) for atopic dermatitis. Conclusions Our findings suggest that some aspects of the farm environment, not just attributable to contact with livestock, were protective for respiratory and allergic conditions among 4-H youth.