The bacterial microbiome is defined as the collection of bacteria and their genomes, which can be either symbiotic, pathogenic, or commensal. Evidence supports the existence of a blood microbiome in humans and animals and differences in its composition in health versus disease. In cats, the bacterial blood microbiome has been investigated in a small colony of healthy kittens. However, the clinical implications of resident circulating bacterial communities in healthy and diseased cats remain largely unexplored. The aims of this study are to (1)describe the diversity of the blood bacterial microbiome of healthy cats by age and sex; (2)describe the diversity of the blood bacterial microbiome of febrile cats; (3)compare the blood microbiome between healthy and febrile cats; (4)compare the blood microbiome within febrile cats according to the affected body system. This study will use stored Genomic DNA samples purified from the blood of cats, obtained from a total of 300 domestic client-owned healthy and febrile cats. The blood bacterial composition and richness will be determined and compared between healthy and febrile cats and within subgroups of healthy cats (male vs female; age [kitten vs young adult vs mature vs senior]) and subgroups of febrile cats (affected body system [Systemic vs Skin vs Respiratory vs Oral/Gastrointestinal vs Systemic/Hematologic]). With this research, we expect to define the baseline for blood bacterial microbiome in healthy cats by age and sex and to understand the role of microbial communities in cats with fever, setting the stage for future applications in the clinical context.