This registry-based retrospective study examined 6,150 units of blood from 1,914 active canine blood donors in order to estimate and predict positivity to transmittable blood-borne pathogens. Of the 1,779 units tested for antibodies, 10 (0.56%) were positive for antibodies against Anaplasma phagocytophilum and A platys, and none had antibodies against Ehrlichia canis or E ewingii. After excluding the antibody-positive units, 1.1% of 6,140 units were found to be PCR-positive for A phagocytophilum, Bartonella spp, Brucella canis, Candidatus Mycoplasma haematoparvum, Mycoplasma haemocanis, or a combination thereof. Units from the first blood collection were more likely to test PCR-positive for pathogens than were units from subsequent collections. The prevalence of transmittable pathogens is low but represents a risk to transfusion recipients, highlighting the importance of screening blood donors, especially those donating for the first time.