The experiment was conducted on newborn hypotrophic piglets obtained from sows of the 3rd–4th farrow on the farm in the Voronezh region. Bone marrow for histochemical and ultrastructural studies was selected from hypotrophic piglets with a body weight less than 800 g (n = 13). The material for electron microscopy was carried out in 2.5% glutaraldehyde in 0.114 M colloid buffer in the cold with postfixation in 1% solution of osmium tetroxide in the same buffer. The material was enclosed in epon-812. Semithin sections were stained with azur-2 in combination with the main fuchsin and were examined under Leica light microscope. Ultrathin sections were prepared on Ultracut (Leica) ultramicrotome, contrasted with lead citrate and uranyl acetate and examined under EM-208 (Philips) electron microscope. In hypotrophic piglets, the cells forming in the red bone marrow are located as islands. Hypoplasia of cells of the hemopoetic series occurred, proerythroblasts and megacaryoblasts were observed in insignificant quantity. Megakaryocytes were closely adjacent to sinusoidal capillaries, and a part of their cytoplasm penetrated into the lumen of blood vessels. Separating fragments of cytoplasm in the form of platelets were transferred to the blood flow. Light mitochondria with a few small electron-dense cristae were observed in the ultrastructure of cells of the bone marrow. The emergence of immature forms, which indicated bone marrow function disorder or its barrier damage, was also observed in the blood flow. At the same time there occurred a decrease in the number of differentiated cells and their differentiation disorder, which could lead to immunodeficiency state. Differentiation of cells in the bone marrow of hypotrophic piglets is impaired, and that is why the body is not provided with a sufficient number of blood cells. Blast cells, which appear in the blood flow, cannot fully perform their functions, resulting in immunodeficiency and anemia.

For the experiment, 3 groups of 40 sick piglets at the age of 5-7 days were selected, in which gastrointestinal tract diseases of mixed bacterial etiology were recorded. The first group was the control one and underwent no treatment. The animals of group 2 were administered intramuscularly the drug "Quinokol". The animals of the third group were administered “Quinokol” in combination with GM-CSF. In the immunе histochemical studies the revealed level of CD-3 positive cells in the mucous membrane in group 3 was found higher than in groups 1 and 2 by 62% and 51%, respectively. This indicates the stimulation of the migration of T cells into the intestine to maintain local immunity.

The effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the functional state of the thymus in the treatment of gastrointestinal diseases in piglets was studied. The experiment was carried out on a large pig breeding farm in the Voronezh region. For the experiment, 3 groups of 20 sick piglets at the age of 5-7 days were formed in which gastrointestinal diseases of bacterial etiology were registered. The group 5 was the control, and the piglets of it did not receive treatment, the piglets of group 2 received the drug Quinocol, and the piglets of group 3 – Quinocol in combination with GM-CSF. Histological and immunohistochemical studies were carried out according to commonly accepted methods. As a result, a significant (p<0.01) decrease in CD-3 positive cells in the field of view by 12% in group 3 was shown, which was a consequence of cell migration from the thymus to peripheral organs. There were no significant differences in the number of PAX-5 cells.

The study presents the data on the level of expression of pro- and anti-inflammatory cytokines in piglets with gas-trointestinal diseases of bacterial etiology. The analysis of gene expression showed that the expression levels of IL-1α and IL-10 were significantly increased in sick piglets, while IL-1β lost its activity. During the histological examination, there were no differences between the structure of the intestines of sick and healthy piglets. However, cytological examination: of the samples obtained from sick piglets demonstrated alteration and a decrease in the adhesive barrier in the epithelium of intestinal villi.