Background: Leukoreduction by filtration (LRF) is a common procedure in human blood banks, and has also been used to reduce the transmission of infectious agents such as viruses, bacteria, and blood parasites. Objective: This study aimed to evaluate the efficiency of filtration leukoreduction in the quantitative control of Escherichia coli inoculated into equine blood bags during 21 days of storage. Study Design: In vitro experiments. Methods: Blood samples of approximately 450 ml per blood bag were obtained from six haematologically stable horses. Bags of whole blood were refrigerated for 2 hours at 2° to 6°C, after which each bag was inoculated with 1 ml of E. coli diluted in Brain Heart Infusion broth, containing 1×10 8 CFU/mL, and then separated into two groups: experimental (n=7) and control (n=7). In the experimental group bedside leukocyte filters with a prefilter were applied. Blood count, osmotic fragility, percentage of haemolysis, bacterial culture, and serum potassium, protein, albumin, and glucose levels were analysed. For descriptive analysis and comparison of means between groups and between times, Tukey’s test and Pearson’s chi-square test were used for bacterial concentration and filtration efficiency, with significance set at a p-value <0.05 in both tests, while the 95% confidence interval (CI) was calculated. Results: The human leukocyte filter was efficient at leukoreducing equine whole blood inoculated with E. coli, without causing any quantitative reduction in the red series or an increase in osmotic fragility. Main Limitations: The study presented a limited number of blood bags and a reduced storage time. Conclusions: Overall, we found a significant reduction in the number of E. coli when using leukocyte filters. The reduction in the number of E. coli cells during storage in both groups suggests a role of factors such as filtration, storage time, and low temperature in bacterial control, in addition to leukocytes.