Cefovecin is an injectable third-generation cephalosporin (3GC) antimicrobial that is frequently administered to cats. However, it is not a recommended treatment for most feline bacterial infections; first-generation cephalosporins, aminopenicillins, or other antimicrobial classes are preferred for common infections. Cefovecin use may select for 3GC resistance, which limits treatment options for bacterial infections. Our goal is to assess the impact of cefovecin on antimicrobial resistance (AMR) among feline pathogenic and commensal bacteria. We will first assess trends in AMR among feline pathogens over the last 14 years. Cefovecin was approved in the U.S. in 2008; we will analyze antimicrobial susceptibility data from Cornell’s Animal Health Diagnostic Center between 2007 and 2020 with statistical models to detect changes in AMR and multidrug resistance (MDR) over time. We expect to identify an increase in 3GC resistance over this time period. By using machine learning to quantify the relationship between 3GC resistance and resistance to other antimicrobial classes, we can understand cefovecin’s potential for selecting MDR. Using a subset of historical isolates with available medical records, we will conduct a retrospective case-control study to quantify the association between cefovecin use and subsequent isolation of 3GC resistant bacteria. We expect to find that recent cefovecin use or other antimicrobial use is more likely in cats with 3GC resistant infections compared to 3GC susceptible infections. Second, we will conduct a prospective cohort study of client-owned cats to examine AMR in vivo following amoxicillin-clavulanic acid administration, which is a recommended treatment for several feline infections, and cefovecin, which is not recommended but commonly used. We will isolate commensal Escherichia coli and enterococci from fecal samples at seven time-points and test them for antimicrobial susceptibility using Kirby-Bauer disc diffusion. A next-generation sequencing approach will be used to evaluate AMR genes. This cohort study will enable us to compare the emergence and persistence of AMR in feline commensal bacteria following cefovecin treatment to AMR following amoxicillin-clavulanic acid treatment. We expect that AMR will be more prevalent and persistent in cefovecin treated cats because cefovecin has a long half-life, which exposes commensal bacteria to sub-inhibitory cefovecin concentrations. Overall, our findings will improve feline health by promoting antimicrobial stewardship to minimize the risk of AMR without compromising treatment success.