In my PhD research, I utilized pre-existing antibodies developed in my laboratory along with a novel IgD antibody, to characterize horse B cell populations in various developmental and immunological states in the peripheral blood. IgD, IgM, and CD23 were used to identify B cell populations earlier in development, while IgG1, IgG4, and CD23 were used to identify mature populations. In the first portion of this dissertation, I delved into the significance of B cell characterization. The sequential research chapters articulated how the incorporation of IgD can be used to better define the B cell profile in the peripheral blood of healthy horses and horses infected with EHV-1, at different stages of development. Lastly, I highlighted two primary antibody isotypes responsible for neutralizing EHV-1 and preventing viral infection, IgG1 and IgG4/7.