Out of the initial selected sets of 16 and 19 factors for fattening pig and sow farms, respectively, only a few factors showed to be significantly associated with the use of antibiotics. Excluding factors that were correlated with each other and selecting the model with the best set of explanatory factors were done with great care, considering underlying biology/physiology as well as statistical arguments. Therefore, the applied selection methodology is considered to have resulted in the best set of explanatory factors, from both biological and statistical perspectives. Obviously, many of the investigated technical and economic factors, like amount of feed used and BW of the piglets, were not associated with the on-farm antibiotic use. The resulting unexplained variance, therefore, may be due to factors from other influential fields. For example, behavioral factors have been shown to affect the attitudes of farmers toward disease control (Ellis-Iversen et al., 2010). Therefore, it is recommended to investigate the potential effect of socioeconomic-related factors, like attitude of farmers and veterinarians toward the use of medicine and risk perception, on the use of antibiotics in future research. Insight into the roles of these factors may help further to effectively address the problem of diminishing the use of antibiotics.