Currently, the use of monoclonal antibodies to study the immune status of animals is the most common in both medicine and veterinary medicine. Monoclonal antibodies were obtained by standard methods using a 2-fold intra-splenic injection of Ig with an interval of 14 days. As a result, an oligoclonal system of monoclonal antibodies to conformational epitopes of cattle IgM was created, specifically interacting with the antigenic determinants of the original, membrane-bound form of IgM, which is the basis of the antigenic B-cell receptor (BCR). B cells are an important structural component of the immune system. The process of antibody formation depends on the number and functional state of B cells. Early detection of target cells, which may be lymphocytes or their subpopulations, is important in infectious diseases. Monomeric IgM pentamer molecules are anchored in the B cell membrane and serve as the basis of the antigenic receptor. In the experiment, the method of immunoperoxidase staining was used, which is based on the detection and determination of the degree of intensity of membrane (sIgM) and cytoplasmic IgM (cIgM) staining. The number of B-lymphocytes in the blood of cattle (25.3±2.6%), sheep (32.0± 2.2%) and goats (20.0±1.5%) was determined. In the blood of calves aged 1 month, the number of B-lymphocytes is 19.2 ± 0.8%. Also, cells with the cytoplasmic form (cIgM) of class M immunoglobulin were found in the blood of calves. cIgM cells can be pre-B cells with cytoplasmic ?-chains or plasma cells synthesizing a soluble form of IgM. It was found that the main form of localization of surface IgM-receptors on B cells of cattle and sheep is an uneven distribution of sIgM along the perimeter of the cell, namely in the form of "patch-endocytosis", which is 68.9±3.9% and 84.0±4.2%, respectively; expression of sIgM-receptors on B lymphocytes of cattle livestock is 8.0high ± 1.0% and 10.5low ± 1.5%, and sheep - 6.3high ± 0.9% and 13.3low ± 0.6%. Thus, in healthy animals, the sIgM-receptors of B lymphocytes are distributed unevenly and with low density in the membrane.