RT article T1 Commensal Escherichia coli Antimicrobial Resistance and Multidrug-Resistance Dynamics during Broiler Growing Period: Commercial vs. Improved Farm Conditions A1 Montoro-Dasí, Laura A1 Villagra, Arantxa A1 Sevilla-Navarro, Sandra A1 Pérez-Gracia, María T. A1 Vega, Santiago A1 Marín, Clara K1 Multidrug resistance K1 L73 Animal diseases K1 L01 Animal husbandry K1 L70 Veterinary science and hygiene K1 L50 Animal physiology and biochemistry K1 Antimicrobial resistance K1 Broilers K1 Farm management K1 Escherichia coli AB New measures applied to reduce antimicrobial resistances (AMR) at field level in broilerproduction are focused on improving animals’ welfare and resilience. However, it is necessary tohave better knowledge of AMR epidemiology. Thus, the aim of this study was to evaluate AMR andmultidrug resistance (MDR) dynamics during the rearing of broilers under commercial (33 kg/m2density and max. 20 ppm ammonia) and improved (17 kg/m2 density and max. 10 ppm ammonia)farm conditions. Day-old chicks were housed in two poultry houses (commercial vs. improved),and no antimicrobial agents were administered at any point. Animals were sampled at arrival day,mid-period and at slaughter day. High AMR rates were observed throughout rearing. No statisticaldifferences were observed between groups. Moreover, both groups presented high MDR at slaughterday. These results could be explained by vertical or horizontal resistance acquisition. In conclusion,AMR and MDR are present throughout rearing. Moreover, although a lower level of MDR wasobserved at mid-period in animals reared under less intensive conditions, no differences were foundat the end. In order to reduce the presence of AMR bacteria in poultry, further studies are needed tobetter understand AMR acquisition and prevalence in differing broiler growing conditions. PB MDPI SN 2076-2615 YR 2021 FD 2021 LK http://hdl.handle.net/20.500.11939/7522 UL http://hdl.handle.net/20.500.11939/7522 LA en NO Montoro-Dasi, L., Villagra, A., Sevilla-Navarro, S., Pérez-Gracia, M. T., Vega, S., & Marin, C. (2021). Commensal Escherichia coli Antimicrobial Resistance and Multidrug-Resistance Dynamics during Broiler Growing Period: Commercial vs. Improved Farm Conditions. Animals, 11(4), 1005. DS MINDS@UW RD May 27, 2022