Association between farm biosecurity practices and antimicrobial usage on commercial chicken farms in Chattogram, Bangladesh.

Commercial broiler and layer farming represents an important livestock industry in Bangladesh. Adequate biosecurity practices are considered to be an effective method to prevent infectious disease occurrence on commercial poultry farms, but antimicrobials are also frequently administered to reduce disease risk. We conducted a cross-sectional study on 57 commercial layer and 83 broiler farms in eight subdistricts of the Chattogram district in Bangladesh to investigate the relationship between implemented biosecurity practices and the use of antimicrobials on these farms. We used a causal diagram framework to inform multi-level mixed effects logistic regression models to explore the total and direct effects of biosecurity practices implemented on commercial farms on prophylactic versus therapeutic antimicrobial usage on these farms. Overall, inadequate biosecurity was more common on broiler compared to layer farms and on farms rearing smaller flock sizes. For example, separation of sick from healthy birds was more common on layer farms (85.2 %, 46/54) compared to broiler farms (38.6 %, 32/83) (p = 0.001). Prophylactic administration (compared to therapeutic use) of antimicrobials was less common on farms that were separating sick birds from the healthy birds (total and direct effect OR = 0.1, 95 % CI: 0.1-0.6, p = 0.006) and less common on farms that used a poorer quality source of water for drinking, cooling, cleaning, and washing (total and direct effect OR = 0.3, 95 % CI: 0.1-0.9, p = 0.036). In contrast, farmers that used washing facilities (versus non-usage of washing facilities) were more likely to administer antimicrobials prophylactically (total and direct effect OR = 3.9, 95 % CI: 1.3-11.3, p = 0.012). The null model ICC indicated significant clustering at the subdistrict level (ICC = 0.20, 95 % CI: 0.04-0.60, p = 0.013), but the ICC was reduced after including flock size and farm type, and the biosecurity practices as fixed effects (ICC = 0.14, 95 % CI: 0.02-0.59, p = 0.0661). Overall, our study highlighted that a large proportion of commercial chicken farmers mediated poor biosecurity practices by prophylactic application of antimicrobials. The results of our research can be used to inform awareness programs for commercial poultry farmers emphasizing the importance of improving biosecurity rather than using antimicrobials to reduce the risk of poultry disease occurrence.